DirtRider . Net MX, SX, Arena Cross, Off-Road Community
Dirt Rider . Net Text Version Home
Dirt Bike Dirt Bike Dirt Bike Dirt Bike

This is the text version of DirtRider.Net
Click Here for the Full Version


Pages: 1

Porting and flow

(Click here to view the original thread with full colors/images)

Posted by: MikeS

I was told by a tuner that just "rounding" the port edges where they meet the cylinder with emery cloth or such is one of the best and easiest ways to help flow.

Is this true ?


Posted by: Rich Rohrich

Quote:
Originally posted by MikeS
I was told by a tuner that just "rounding" the port edges where they meet the cylinder with emery cloth or such is one of the best and easiest ways to help flow.

Is this true ?


No. Port flow is quite a bit more complicated than that, plus on a two-stroke bulk flow is rarely the issue. Time-area relationships are far more critical.


Posted by: MikeS

Rich
Assuming port timing/area is optimized for the application, is the shape/angle of the transition from port to cylinder critical or is just a clean up with the grinder all that is needed?

In a 4 stroke the valve pocket and seat angles play a role in flow...correct?

Being extremely General would be a basic plumbing fixture like a Tee fitting . Rounding or adding a certain radius on the inside area where one section meets the crossing piece, Would flow be enhanced?

Another project for Junior to explain in science class..but this maybe way over his head and me too....


Posted by: gblair

Mr Rohrich is correct as in a...
2st engine-
the bulk flow is out of transfer ports and into the cylinder so rounding that edge has no effect...and the amount of rounding of the exhaust port edge that can be done is so insignificant also to have no effect on the flow coefficients..however one of the truly neglected areas for improving transfer port flow is at the crankcase exit to the transfer ports and here smoothing and rounding of the edges will assist an increase to the discharge coefficient at that location....(but don't gouge forever and decrease significantly the crankcase compression ratio)
4st engine-
..any movement to recess the valve into the head and make a pocket out of it will 'mask' the valves and decrease the discharge coefficient.
..and you can read more on this subject in SAE papers and in SAE references R-161 and R-186.


Posted by: nephron

Quote:
[size=2]..any movement to recess the valve into the head and make a pocket out of it will 'mask' the valves and decrease the discharge coefficient
[/size]

 



I'm sure that MikeS's reference to "valve pocket" was probably meant to refer to pocket porting around the intake valve guide casting/boss.


Posted by: DEANSFASTWAY

If you round or smooth the port edges with emery cloth if not done properly you may be inviting your Nikasil or other cylinder plating to start peeling and coming unbonded .


Posted by: MikeS

Quote:
Originally posted by nephron
[/size][/font]

 



I'm sure that MikeS's reference to "valve pocket" was probably meant to refer to pocket porting around the intake valve guide casting/boss.


Yep that was one part I ment and also on a 4S it would be the transition area in to and including the valve seat. In auto building years ago there was 3 angle, 5 angle seats etc that we played with. In the 2S I meant the sharp or chamfered edge where the port meets the cylinder. Making this round or a specific angle to the chamer would it help flow.

So from the answers here I get a NO.

Thanks guys


Posted by: EricGorr

Regarding the port edge "rounding" on plated cylinder bores a small burr forms on the port edge during the electroplating process. The electrical current arcs to any sharp edges and produces a build-up of material. During the honing process only half of the burr is removed, the part protruding into the bore. Sometimes that burr can be a real hinderance especially if its a small bore cylinder. Here is an example, on a KTM65 the OEM plating wall thickness is .006in so a burr of approximately .012in. can form on the port edge which on that short stroke can represent a few degrees of timing. The only OEM that hand grinds the port edges is Yamaha.

When people call me for tips on the KTM65 I explain the burr problem and another significant problem, the shimming of the cylinder height with base gaskets in order to get the proper timing and squish clearance. Using one of Professor Blair software programs that helps illustrate squish velocity, one can immediately see the difference by reducing the squish clearance to suit a better grade of fuel (race gas). Its just a matter of carefull measuring and trial and error experimentation with a combination of the 7 different base gaskets that KTM offers for that bike. For the port edge, I use a right angle tool with a tiny cylindrical CBN tool bit. I try to grind down the burr without changing the entry angle, and I try to make the roof of the transfer relatively smooth because I remember reading one of the Professor's papers on the laminar flow that occurs for a short time when the transfers open (assuming that adequate blow-down has occurred).

On the 4-stroke engine, Professor Blair's description of recessing the valve into the pocket refers to removing the masking. Its easy to see the performance loss using even a low powered flow bench. This is probably the biggest mistake made by guys who bill themselves as four-stroke porters or gas-flowers. When you look into the combustion chamber there is a narrow margin of shrouding around the valve seat. Thats there for a reason, to aid low lift flow. When you do a flow test before and after mods, the low lift flow could drop in half by grinding down these seemingly insignificant masking shrouds.

In fact thats one of the three observations that Rich and I use to critique a tuner's expertise when we examine ported heads. The most common mistakes are 1) grinding down the shrouds 2) mirror polishing the intake port 3) removing the anti-reversion steps in the exhaust port

In another post on porting 5-valve heads, Professor Blair cautioned that porting these types of heads could disturb the nature of the swirl and tumble characteristics of the head. This is a subject that's hardly ever addressed by tuners, and the "jury is still out" on the YZF. Four-stroke engine scavenge the combustion chamber with a swirling or tumbling of the incoming charge. Swirling is associated with low rpm engines and tumbling is associated with high rpm engines. Four-valve heads are natural tumblers. Rich and I have speculated that the five-valve head on the YZF could be intended by the original designers as a combination head, swirling at low rpm and tumbling at high rpm. We've even had some heads by fitting just the center intake port with a larger valve to produce more tumble and fitting only the left port with a bigger valve to produce more swirl.

Our SWAG (Scientific Wild-Assed Guess) was that we could produce a better cylinder head service for guys with YZFs who mainly rely on the low end pull for enduro or mx, and a distinctly different head for DTX and supermotard. But the "jury is still out" on that little project because we don't have the proper tools or knowledge to prove our SWAG.


Posted by: MikeS

Great info Eric and Professor Blair.

Time to read some SAE papers


Posted by: nephron

Quote:
[size=2]Its just a matter of carefull measuring and trial and error experimentation with a combination of the 7 different base gaskets that KTM offers for that bike
[/size]

[size=2]lol, you make it sound like any of us could just DO that all day long. :thumb: [/size]

[size=2]I'll bet when those minidads call in with questions like that, and you give them that statement, they just throw the cylinder in a box and send it to you. It's kinda like having a patient call in and say something like 'I ripped my arm off today, what should I do?', lol[/size]


Posted by: EricGorr

Nephron,
Thats funny, no actually minibike dads are real skeptical when I explain this to them. I tell them they can send the whole engine and with shipping it runs under $125 and they retort that I must not know what I'm doing because ABC Racing told them that they can make 34hp with their Stage 7 porting that sells for only $2399.95 Its sad but when you try to be honest with people and save them from the sharks they think you're dishonest and dive head first into the shark's open mouth.

And I'm not exaggerating about the Stage 7 stuff @ $2300+$, SFO sent me a web site address the other day for a Cannondale dealer that will gladly ruin your engine for big bucks. Yep they'll reprogram a fuel injection system that has a trim control on the handlebar. Or polish the snot out of the intake port so the fuel just dribbles into the combustion chamber. I think they call it "Reverse Atomization" or something equally as clever.


Posted by: nephron

lol, it all goes back to their high school days when their friends would "port and polish" everything under the hood.

By the way, are you doing any CNC stuff yet--or do heads, etc. change too frequently to make writing a program worthwhile?


Posted by: SFO

Quote:
Originally posted by EricGorr
And I'm not exaggerating about the Stage 7 stuff @ $2300+$, SFO sent me a web site address the other day for a Cannondale dealer that will gladly ruin your engine for big bucks. Yep they'll reprogram a fuel injection system that has a trim control on the handlebar. Or polish the snot out of the intake port so the fuel just dribbles into the combustion chamber. I think they call it "Reverse Atomization" or something equally as clever.



I emailed this guy and asked him to send me the baseline flow chart and the post porting flow chart to back up his claim of a 10% increase in flow.
I was also interested in seeing his dyno run that would back up his 60RWHP claim. Uhhhmmm, still no answer....
But that doesn't stop guys from posting on other websites repeating his claims and justifying the 2300$ they just spent....
You gotta wonder :silly: :silly: :silly:


Posted by: marcusgunby

Is that 60hp on a big bore KX250 by any chance??


Posted by: SFO

I don't want to starta flame so I'll just shut up :scream:


Posted by: marcusgunby

I wish i could have seen your post before the edit


Posted by: MikeS

Whatz alittle heat.....If they can't stand the heat then saty out of the kitchen...

Sorry, Like Eric said alot of this stuff out there. Some guys do a great job but charge $$$$$ for it. I guess that is ok but as it is mentioned here in the forums it ain't all rocket science. Oh unless Rich gets involved


Posted by: EricGorr

Nephron, actually I am looking at CNC porting technology with great interest. The prices are falling and the latest trend is towards software that traces a finished port. So programming time isn't a big issue anymore.
Rich and I are going to the Performance Racing Industry show at Indy on Friday. We'll be reporting back to you guys on machinery, technology, prices, and web site links.
The PRI show features one hall with running machine tools that you can test drive. You can do stuff like TIG weld, port heads, CNC machine blocks, hone and bore. Its unbelievable! And this year because of the economy a lot of companies are doing lease to own programs with zero interest.
Rich is gonna go nuts


Posted by: luvtolean

Quote:
Originally posted by EricGorr
Nephron, actually I am looking at CNC porting technology with great interest. The prices are falling and the latest trend is towards software that traces a finished port. So programming time isn't a big issue anymore.
Rich and I are going to the Performance Racing Industry show at Indy on Friday. We'll be reporting back to you guys on machinery, technology, prices, and web site links.
The PRI show features one hall with running machine tools that you can test drive. You can do stuff like TIG weld, port heads, CNC machine blocks, hone and bore. Its unbelievable! And this year because of the economy a lot of companies are doing lease to own programs with zero interest.
Rich is gonna go nuts


That is a show I must make sometime in my life. That would be too cool.


Posted by: nephron

Eric, a curiosity to me about CNC porting a bike with one cylinder, is that a lot of the gains on a V8 are due to making every port and chamber identical. The newfound symmetry apparently profers most of the gains. There are even those that will hand finish the heads AFTER CNC'ing, as in Pro Stock type applications.

It seems to me that your gain might be repeatability from bike to bike, and just flat making the job easier. But I'll go out on a limb here, and predict that a CNC job, even if modeled after one of your hand ported cylinders, isn't going to make anymore power than you're already doing. What do you think?


Posted by: MikeS

Eric

You mentioned once that you thought about a bigger garage :scream: ..I doubt that Rich can fit a 4 axis CNC up the stairs to his place....

I wish I could check that stuff out.... you guys are just too dang far away.

Mike


Posted by: SFO

Rich and Eric,
Say Hi to Mike Perry at the KMPI booth.
Booth #3998

Also check out the Mira line of seat cutting equipment. (The centronic.)
Booth #4218/4220

And the Arrow Precision company.
Booth #4224

Wish I could go!

You are going to want to check out coordinate measuring machines, CMM's, for creating models of ports too.


Posted by: Shawn Mc

Eric, If you want to see a machine, call a guy named Manuel Turchan.

He builds a milling machine that will blow your mind.

How about drillng and tapping at 100,000 rpm and in a single motion! No lie.

He has machines that will machine a raw casting into an assembleable engine block in 6 seconds.

I used to work for Hughes Aircraft and we investigated a couple of his machines for milling titainium, which he does at 30,000 rpm. The chip actually comes off in a gas!


Posted by: Rich Rohrich

Quote:
Originally posted by SFO
Rich and Eric,
Say Hi to Mike Perry at the KMPI booth.
Booth #3998


Eric and I are going to buy Mike dinner on Friday night and pick his brain :thumb:


Posted by: SFO

[QUOTEEric and I are going to buy Mike dinner on Friday night and pick his brain :thumb: [/B][/QUOTE]

Cool!
This is a link to the show if you are in Indy.

http://www.performanceracing.com/index2_lcp.html

This thing is very big so try to get a whole day for it.


Posted by: Jman271

Hello guys, just a few questions regarding the 65sx squish topic. EG mentioned that to obtain the proper squish you have to experiment w/ diff thickness base gaskets. Has there been instances where more than one gasket is needed at a time, as in a double base gasket? Also,(w/o knowing the desired squish clearance #), is there a base line # that you guys shoot for? Like if it falls between .038-.042 it is OK? How much is too much and how much is too little? And lastly, why is it that there are so many gaskets? Doesn't that leave the door open to make your little bike run worse if you get a wrong gasket combo from the dealer? Why not do it like the others and make 1 gasket that is in the middle of the road, and then leave it up to the tuners to mill the base/head to get the desired squish#? Sorry if I asked a lot of questions but I am trying to understand the theory and what has to be done to make it all work out. Like if you mill the head to get desired squish, but leave the base alone, you may have gotten the target # correct, but it didn't really help the timing of it all w/ the ports etc. Rich R, or EG can you tell me if I am heading in the right direction? Have a safe trip-


Posted by: sunrise

What it will do, is to allow all the kids on the block to have the same port job +-.0002".

Maybe with all the kids wanting, the CNC PORTING MACHINE will be nice and allow all of us, to have a good Idea in performance, CHEAP...


Posted by: marcusgunby

Like sunrise said, it allow all production bike to have the same port timing,i bet alot of jap bikes are set up incorrect because of production tolerances.You need many gaskets thicknesses to ensure every bike can be set up correctly.You can and often will need to double up on gaskets.


Posted by: luvtolean

Quote:
Originally posted by Shawn Mc
Eric, If you want to see a machine, call a guy named Manuel Turchan.

He builds a milling machine that will blow your mind.

How about drillng and tapping at 100,000 rpm and in a single motion! No lie.

He has machines that will machine a raw casting into an assembleable engine block in 6 seconds.

I used to work for Hughes Aircraft and we investigated a couple of his machines for milling titainium, which he does at 30,000 rpm. The chip actually comes off in a gas!


That is impressive stuff. Do you have a linky? I won't be buying one anytime soon(so I don't want to bother him), but I'd like to see it.


Posted by: EricGorr

Nephron,
Mahle in Germany is the biggest manufacturer of motorcycle cylinders in the world. They use CNC porting for rough castings prior to electroplating to reduce hand-labor costs. My personal concern is that at 45 years old and 40,000 cylinders under my belt, that I will eventually suffer from some wrist malady or lung disorder. And I do take safety recautions but as you know better than most of us, the human body has its reliability limits.
I've also looked at abrasive flow machining, using polymers with diamond abrasives to finsh ports.
The obvious choice is to train people, but as I've learned through experience thats a dead-end scenario. They either get a disability or become your competitor. People never work out, machines never quit working.
Right now with the state of technology I estimate that it would cost $80,000 and 1,000 hours to set-up a CNC porting system to handle 80% of the labor tasks.
If my health ever gets to be an issue I'll bail out on this machining thing and write books. Thats the ultimate lifestyle!


Posted by: IcerDave

Our previous company set up a cnc operation of an exhaust port on a Yam sx700 cylinder. It was done on two different stations. Basically each side was done at a time. It was huge labor savings cuz quite a bit of material was removed. Just a little sanding roll cleaning was needed post machining. Now to get to tarnsfers and intake might take a little more think time :-)


Posted by: EricGorr

I saw a multi-angle grinding head for a 3 axis CNC mill in the J&L catalog for $2,500 it accepts 1/4inch bits and can not only cut the roof angles of the transfers, when you install the ball end it can chamfer the ports. The new KX125 cylinder has a bit of overkill with the CNC chamfer but it doesn't need any post plating deburring prior to honing.
The Germans don't mess around, they know how to save human labor, and you've got to love a nation that has beer and sausage breaks at 10am and 2pm


Posted by: jmics19067

Eric,
If you train me and promise me beer and sausages at 10 and 2:00 I promise I will never become /work for a competitor . But I just want to know does workmans comp cover heartburn and hangovers?


Posted by: IcerDave

Can I get on that B&S (beer and sausage) list? No worries for my nickel cadmium plated cast iron stomach. I can eat and drink just about anything


Posted by: gblair

...a quick tip to all on 2-stroke engines..
...as scavenging can easily get to be unsymmetrical due to unequal port heights on sandcast or even diecast 2-stroke engine cylinders, one of the critical dimensions you can investigate on your own cylinder is the height (from bore top edge) of the opening of each of the main transfer ports, and each of the side transfer ports, and (file or grind) to make them identical at the relevant opening edge from side to side of the cylinder. That way at least the exiting flow of fresh charge will be identical from each of the component PAIRS of transfer ports and the scavenging flow will be symmetrical within the cylinder...note that I did not say it would be good scavenging necessarily but simply that it would be symmetrical and that is always the first step to good scavenging. Mind you, I am sure that Messrs. Gorr and Rohrich must have mentioned this in some earlier forum on 2st engines.


Posted by: marcusgunby

Hello again right my question regards the latests version of the carb divider wing-the ones i have seen in the past have been on the reed side, and many have found its hard to get the jetting dialed in as the divider must play havoc with the mixture on anything past half throttle-the later version is on the airfilter side-it fits on the bell mouth of the carb see link www.worldpowerracing.com whats your feelings on the design-does it have merit?thanks marcus.


Posted by: gblair

..to Mr Gunby...
...without conducting a flow visualisation test on this flow straightener device, I find it hard to see what carburetion effect this flat plate provides...but as long ago I have learned never to second guess fluid mechanics and its effects, I hesitate to say that I cannot see any benefit coming from its use other than as a simple flow straightener just at the carb venturi..which may help the carburetter to provide a more even mixture control over the speed range...but at this point in advance of such a proper test to confirm (or otherwise) its effectiveness I remain somewhat sceptical about it, particularly at full throttle.
There is no doubt that below about half-throttle the air flow will be more clearly directed at the aperture of the venturi of a slide carburetter where the fuel appears from the bowl...and this may indeed provide somewhat better air-fuel ratio control by the carburetter...now I can see some potential benefit here.


Posted by: steve125

I have installed a Power Now in a 03 CR 125. The "hope" in this device is to allow these big 38mm carbys, that are being speced on all late model 125's. To respond better at lower throttle openings, as with some there can be a bit of a dead spot. That is the puzzle, is it a jetting issue or an air speed problem or a combination of the two? So far the only thing I have noticed is that the PN has richened my pilot circuit a bit, after a 1/2 turn out on the air screw it's ok now. The throttle response seems quicker, but as for how it runs on the track the weather has kept me from rideing. It will be an easy part to remove and then reinstall at the track, I will report back on my findings.


Posted by: gblair

..things are very quite in here!...I posted a porting tip above and nobody came back and said either..'wow' or 'absolute rubbish' or 'we heard that one before'!....so let's hear about it!!..

..or are folks all off grinding port pairs to equal heights from tdc and then testing them out before coming back and reporting in with their findings!


Posted by: steve125

Thanks for the wake up call as the weather has me behind in my testing! Ok a question. What do you feel are the advantages or disadvantages of staggered transfer port timings? Do you feel all transfers should open at the same time or should the primaries open first then the secondaries and, lastly, the rear boost port? As you know on modern day mx bikes the carby is mounted at an angle to allow room for the rear shock. This can cause the main intake flow to always favor the right side of the reed block. The manufacturers try to straighten this flow with reed cage inserts, but i'm sure the flow is still offset ( as the right side reeds always fail first). With this offset flow in crankcase filling, how much effect do you feel it has in the equal transfer port scavenging?........thanks!


Posted by: marcusgunby

Hi again i have more questions if you dont mind,
On all late model 125 mxers they come with 38mm carbs-some tapered at the reed side to 40mm-im very sceptical of this trend as i cant see how a taper outwards to 40mm and then a taper to the reed mouth of 32mm is any use(in other words, why taper up to 40mm if the reed entrance in only 32mm across)also on carb sizes the old rule was small carb(35/36mm) for bottom end and large(38) for top, now modern 125s have 38mm with really good bottom end and the KTM has the huge 39.5mm carb and it has more bottom than the others-do you think the old rules were good at making up for bad port timing and other issues?KTM seems to think get the biggest carb ever and make the rest work around it and who can argue-best engine for the last 4 years.


Posted by: ochster

I've also thought it was an attempt at messing with velocities, sorta like a velocity stack.


Posted by: marcusgunby

ochster i have heard of the velocity stack but have no idea what it is-can you enlighten me?


Posted by: ochster

Back in the day, on many Hot rod carbs, it was simply a tapered bell that fit on top of the carb. Many times a foam element was on top, for basic air cleaning. Supposedly it corrected, and or was a better transition, to direct scavenged air into the carb. Hope that makes sense.


Posted by: Rich Rohrich

Marcus - The red bell in the picture is considered a velocity stack .


Posted by: ochster

Rich, pertaining to Marcus's post. Would you say there playing with the bell taper angles, to manipulate the air velocitie? Is this a common tunning tool? it appears so in your photo, with the replaceable bells.


Posted by: gblair

to Steve 125..
..the thinking behind the staggered port timings is to get the scavenge flow moving towards the rear of the cylinder away from the exhaust port but as all flow at the transfer port opening at full load and high speed is BACKFLOW into the transfer ports from the cylinder that would seem to negate the argument. However, when the real flow commences that from the main transfer ports is then coming out of a port with a larger area and so its momentum in the desired direction is always somewhat higher and may well accomplish the designer's thinking. During scavenge tests at QUB I do not recall an engine with staggered transfer ports out-performing one with ports at equal timing.
The 'bent' intake port will have little effect on such events as the thrashing flywheels and the fairly large crankcase volume will virtually even out the flow behaviour at the transfer port exits.


Posted by: gblair

..to Mr Gunby..re tapered reed blocks...
I can only but presume that they (KTM) experimented with the larger carburetter and also larger reed block widths than 32 mm at the tip but in the end found that the standard 32 mm reed block width with a 40 mm width to accommodate the larger 39.5 carburetter was the best outcome. Not having modelled that set-up on the VIRTUAL ENGINES simulation that is the best I can come up with as an answer!


Posted by: Fark

Mr Blair, I stumbled on your tip a little too late! My cylinders are hopefully safely in EG's hands as we speak... you can bet I'll be looking at them a little more closely when they return.

I don't have a great understanding of fluid dynamics and two stroke engine port tuning . Can anyone recommend a book on these subjects or similiar written in laymens?

And thanks for finding the time to come in and chat with us. Imagine our delight when we meet our hero's hero!!

I have to compliment your newfound typing skills too! You've grown inleaps and bounds AND found the shift button I see...

Just some freindly ribbing.. thanks again for dropping by.


Posted by: Fark

Hero's should be plural up there... as in heros'.

 

  :thumb:


Posted by: steve125

Thanks for answering Professor Blair. A more basic question that i'm sure alot of readers would like to hear your comments.  Alot of us old timers believe in the more oil the better in our racing 2 strokes. We do this because we believe it will allow a better ring seal and the result will be more power through out the rev range. So does this indeed happen, say running a 20-1 vs a 40-1 and leaving jetting out of this equation.  Also and if so,  do you feel a bean oil has an advantage in ring seal over a petroleum or a synthetic given the fuel oil ratios are all the same? The reason I ask back in 87 the 125's that I was tuning had some cylinder base gasket leakage problems. When testing a new castor oil that was out at that time, I discovered that when I used the castor fuel oil mix the base gaskets would stop leaking! When I switched back to my old petroleum fuel oil mix at same ratio of 20-1,  the leaks (small) would return.


Posted by: bclapham

Prof Blair, i have a couple of basic questions also regarding bolt ons.

there seems to be a lot of anecdotal evidence for performance increase using the moto tassinari v-force double reed system (4 petals). is there any scientific data backing this up, and if so why does this mod worrk so well? I noticed our resident tuners steve and marcus found (i think they did anyway) that the v-force made little difference on some of the 03 125's, is it just a case of the manufacturers just not updating their designs often enough....my yamaha reeds are the same part numbers for at least 5 years! that said i spoke with some factory honda techs at the races and they sweared by this mod (not that this means much).

the other Q is regarding FMF's SST pipe, ive looked at mine, it seems to narrow quite a bit at the last section, then widens just before the silencer. again, a lot of people feel they are getting good results with this pipe, real deal or placebo?

appologies for my basic questions, but then i am a basic kinda guy!

also, thanks again for sharing your knowledge here ......unfortunately, no one really wants to know about my endevours using solid-phase rhodium insertion reactions to generate chemical diversity for drug discovery, its not nearly as interesting as motorbikes!!!!.... :thumb:


Posted by: gblair

to Fark...

..seeing things are getting a bit picky...the plural of 'hero' is 'heroes'...at least where I come from anyway!

..and as to a book try the R-161 book reference in the SAE bookstore at www.sae.org or click on the very same reference in my website at www.profblairandassociates.com and it will take you straight to it at SAE or Amazon.


Posted by: gblair

..to Steve125..

I have no personal knowledge that a castor base oil is any better at gasket sealing than a mineral base oil and in the 70's when we were racing the QUB500 2st engine in road racing and using either type of oil from time to time I noticed no such effect.


Posted by: gblair

...to bclapham...

I don't think I ought to comment on the performance characteristics of one manufacturer's reed petals or exhaust pipe vis-a-vis that of another...they are all going to behave differently on different 2st engines anyway due to the differing porting and scavenging tuning characterstics designed into the differing engines. That is why the use of an accurate and detailed engine simulation (see VIRTUAL 2ST at www.optimum-power.com) is so important in determining for the engineer that which will aid his design to perform in a superior fashion over the speed and load range on the track.


Posted by: steve125

Professor Blair could you answer the first part of my last question. On the idea that a 20-1 mix will allow a better ring seal than say a 40-1. Thanks!


Posted by: Fark

HAHAH good eye Mr Blair! I ah.. put that like that on purpose, I figured you needed the ammunition... right.

I also am curious about the great premix debate. I trust Eric's words and use what the MFR specifies... 50:1 for Bel Ray MC1. Then I read about these guys using 20:1 with MX2T.

I guess I just like the pretty white bottle and fuel.


Posted by: gblair

to steve125..

..forget your 20:1 mix question...but I cannot help here as I never saw or heard of any evidence that EXCESS oil on a cylinder wall aids ring sealing. If the engine functions correctly at 40:1 mix then a 20:1 mix is an EXCESS of oil and may introduce more sliding component drag elsewhere on the engine, e.g., sticktion slowing down initial reed lift, etc.


Posted by: MikeS

Oh boy! another oil can of worms.

I think the key phrase here is "if the engine functions correctly"

As always thanks gblair.


Posted by: steve125

Thanks again Professor Blair! Well then it seems that the oil migration issue is of greater importance when deciding on an optimal fuel oil ratio. link here>www.maximausa.com/technical/oilmigration.html


Posted by: bclapham

great article steve! its funny how a concept that has been used for years in medicine to assess the workings of the human body has found its way into the investigation of 2-stroke oil! its also funny that we start off talking about highly complex 2-stroke tuning issues but we end up talking about what oil ratio to use!...back to basics!


Posted by: steve125

Yes Bruce even the basics have to be rethought sometimes. And to MikeS I think the other key here in Professor Blair's post is the word: EXCESS!  :thumb:


Posted by: gblair

to Steve125..

thank you for the interesting link on oil migration times...


Posted by: MikeS

Steve125
Thanks...dang I missed that article somehow.

I agree on the Excess too. In my many conversations with Rich, Dr Redzus, and others one key element was always stay conservative with oil (16-20:1 with small bores) then adjust (reduce oil) for maximum peformance (both power and reliabilty).

Running juniors 85cc 24:1 mix in my 300 has no real advantage other than to reduce the insect population

Great info guys


Posted by: bclapham

Yep, if your out there listening Rich, it would be good to hear you comments on this oil ratio subject. If i remember, i think Rich saying he did some dyno runs and got good results down to around 16:1, but i cant remember which applications and the other deatils!

this might sound daft to some, but despite really trying to mess with the jetting on my 250, i still had a bit of spooge at 32:1 but none at 40:1; however, this could also be attributed to my brand of fuel having a high aromatic content. That said, i will stick with 40:1 since i dont see wide open throttle that much!


Posted by: MikeS

It seems that I keep looking over my shoulder just waiting for Rich to bounce in here

b I agree with you on the 250. I have gone full circle with certain oils to get a "clean burn" in my KTM 300. I sort of stay at 28-32:1 only because we run that fuel in the TM125 (150 EG). When I ride the 300 I still get spooge since I am a big guy and ride a gear high. Junior hops on and rides it agreesively and the 300 runs clean. So your statement of not seeing WOT alot is correct. Observations like this just ad to the Oil Mix

WOW this thread has touched on a bit of everything.

Hey gblair,

Sir just another twist to the porting and flow question.

How does tweeking the area around the crank halfs effect performance ? I have seen some engines with epoxy added and others ground out with the dremel tool.

Also how critical is the area above the crank where the cylinder mates ?

Mike


Posted by: gblair

to MikeS..

...never, ever, obstruct the flow into the transfer ports from the crankcase...however, if you want to smooth the entry to those ports without obstructing the flow nor detracting (too much) from the crankcase compression by adding volume then go right to it.


Posted by: steve125

Professor Blair, a question on flow through an expansion chamber. If one were to build 2 pipes that are the same in dimention. But one pipe is straight out from the exhaust port the whole length of the pipe including the stinger and the other has to be curved to fit a motorcycle. How much if any HP is lost on the chamber that has to be bent and curved to fit the bike? How important is it that the head pipe stay straight for as long as possible before curving up the side of the motorcycle? I know this is a general question, but any insight would be appreciated! Thanks!


Posted by: bwalker

Steve, On a three cylinder snowmobile its very significant. A certain company i know of made HP claims that where always higher than everyones else, but where not backed up by the butt dyno. After talking with a former employee i found out that the advertised hp was for straight unformed pipes.


Posted by: bwalker

DR Blair" First let me say its a honor to speak with you. My question is this. What advances have been made in regards to DI two strokes? Have transitional throttle repsonse issues and low rpm ceilings been solved?


Posted by: gblair

to Steve125..
re bending of pipes..if the diffuser section is not bent (ie from the port to the start of the mid-section) there is very little hp loss from a straight pipe...but if it is bent at all then design compensation has to be made, and can be made, to restore some, but never all, of the lost hp from a straight expansion chamber. So it is not just a question re the bending of a 2st pipe, but where it is bent.


Posted by: gblair

to bwalker..
Orbital in Australia totally solved all problems re 2st DI engines including the ones you talk about and right up to 100 car tests over 100,000 km durability range for both durability and emissions longevity....to find out more search the SAE paper archives looking for 'Orbital' or author names such as R.A.R. Houston or M. J. McNiff(ex-QUB students) or K. Schlunke or S. Ahern over the last five or even ten years.


Posted by: steve125

Here's an interesting link on water injection to control the heat of an expansion chamber and therefore, it's tuned length. It's a common practice on most personal watercraft. Professor Blair, have you come across any other examples of a automatically tuned length adjustment system for expansion chambers? link> www.suzuki-rg500.com/water.htm


Posted by: bclapham

i am sure i read or heard that honda were using water injection on Mick Doohans 500gp bike a few years ago, is there any truth to this?


Posted by: gblair

..to the water injection questioners...

....if memory serves correctly, R. Fleck et al from QUB published a paper containing information about water injection into 2st exhaust pipes...so you can try searching the SAE paper archives...


Posted by: gblair

more on water injection...

..again if memory serves correctly, it is a legal requirement that all exhaust pipes on marine craft have to be water cooled either internaly or externally...whether they be 2st or 4st engines.


Posted by: TM-Frank

Quote:
Originally posted by gblair
...it is a legal requirement that all exhaust pipes on marine craft have to be water cooled either internaly or externally...


Why?


Posted by: luvtolean

To reduce the risk of engine compartment fires.


Posted by: 2strok4fun

Firstly let me say thank you to professor Blair for contributing to the forms at DRN. Your contributions to motor sports are huge and the reason why my bathroom is cluttered with technical reading.

In regards to water injection, I have a little (very little) experience using water injection. It is on a personal water craft (Rotax powered). I added an aftermarket water injection that turns the water on at 1500 rpm and then off at 5500. On the stock pipe, supposedly tuned to 6800, there was a noticeable boost in just off idle acceleration, about 1 boat length to a similar un-injected ski. While the increase is noticeable, it is very low in the rpm range for most riding situations to take advantage of. It did however allow me to jet down the existing water injection and I picked up some additional rpm on top.

I am looking at modifying my stock pipe to take advantage of the water injection and increasing top speed without loosing too much bottom end. I am looking at modifying by machining some material from the exhaust manifold (2 into 1) and remove some length before the cone. But determining the amount to remove or whether to remove is where I am at currently. Because of limitations to mounting the pipe I am only able to machine off 6mm from the manifold and head pipe area, but would be able to take up to 28mm from the area just before the converging cone. Using the 199 deg EO, the length of the stock pipe, and a calculation for adjusting speed of sound for temperature, I get the average temp of the pipe to be 268 deg C. If I remove 6mm from header and 26mm from the mid section, I calculate the LT to be 190 rpm higher.

My concern is removing that much volume (not length) from the mid-pipe, I don’t know what effect this might have.

Am I on the right track or am I blowing smoke.

Thank you,
Chris


Posted by: gblair

to 2strok4fun..

..there is not nearly enough geometrical detail on your modifications for me to make a comment (good or bad) but it sounds as if they are quite logical although 32 mm less length to shift by only 190 rpm (on what present peak power rpm?) doesn't quite feel right!


Posted by: 2strok4fun

Proffesor Blair-

Of course you would need morre geometric detail, but you are armed with facts, I can hack at it think I am doing somthing good and be non the wiser.

This was my formula: This could be the source of error.

Tuned length in inches= (EO deg x speed of sound in fps) / rpm
speed of sound in meter/second= 331 + (.06 x temp C)
speed of sound converted into fps for first formula.

I cant remember where I got the formula for speed of sound.

The stock pipe is tuned at 6800 with stock water injection (constant)
I am able to get 7050 with minor motor mods and drying the pipe by using jets fitted to injection point. But that runs the pipe pretty hot inside the enclosed engine compartment. :flame:

I know this isnt Bike related, but at least it is 2-stroke, even if watercraft technology seems to be ten years behind dirt bikes.

Chris


Posted by: Rich Rohrich

Quote:
Originally posted by gblair
..to the water injection questioners...

....if memory serves correctly, R. Fleck et al from QUB published a paper containing information about water injection into 2st exhaust pipes...so you can try searching the SAE paper archives...



SAE # 983072 Measurement of exhaust gas temperatures in a high performance two-stroke engine Publication Date: 11-01-1998
Abstract:
The performance characteristics of two-stroke engines are highly dependent upon the gas dynamic wave action in the exhaust system. In a tuned high performance exhaust system, negative suction pulses aid induction of charge into the cylinder, while positive waves aid its retention. The timing of these waves is closely related to the acoustic velocity, and is therefore dependent on the exhaust gas temperature (EGT).

In advanced engine management systems, the control strategy may be tailored to influence the EGT, and to maximize the beneficial influence of the gas dynamics in the exhaust. Therefore, accurate measurement of EGT is required for development purposes, and real-time feedback could potentially be used as an input to the management system. However, accurate measurement of exhaust gas temperature is fraught with difficulties due to a number of sources of error. Steady state errors can arise due to conduction and radiation of heat from the thermocouple junction, while in transient operation, additional errors arise due to the slow responses of the robust thermocouples which are required to survive the harsh environment.

In this study, the influence of the thermocouple geometry on the steady state errors has been estimated, and a technique has been developed to reconstruct mathematically the instantaneous temperature from the output of two dissimilar thermocouples. Results are presented to demonstrate that the reconstructed temperature correlates well with measurements from a fast-response thermocouple.

Author(s):

Name Affiliation
Robert J. Kee Queen's University of Belfast
Paul G. O'Reilly Queen's University of Belfast
Robert Fleck Queen's University of Belfast
Paul T. McEntee Optimum Power Technology


Posted by: 2strok4fun

So without several fancy thermocouple's, trying to come up with a good length is a shot in the dark.


Posted by: Rich Rohrich

Quote:
Originally posted by 2strok4fun
So without several fancy thermocouple's, trying to come up with a good length is a shot in the dark.



That's the reason software simulations like Virtual Two-Stroke, Dynomation, and the TSR Pipe program exist. :thumb:


Posted by: luvtolean

Quote:
Originally posted by 2strok4fun
So without several fancy thermocouple's, trying to come up with a good length is a shot in the dark.


Well...2 TC's. And some fancy mathematics.

Rich, have you ever attempted to correlate the results of any of these software packages and real world testing?

As my boss likes to say, models are great, but it's only a F____ing model. Show me some data.


Posted by: gblair

to luvtolean..

I agree with you...an engine simulation (or indeed any mathematical) model which has not been correlated with experimental data is totally useless for design purposes....which is why I and others from QUB have been writing books and papers on this subject for some 40 years! See the SAE archives and the SAE R-161 and R-186 textbooks for the information you seek in regard to VIRTUAL 2-STROKE and VIRTUAL 4-STROKE engine simulations and the SAE archives for similar types of papers on results from other engine simulation packages.


Posted by: gblair

to 2strok4fun...

..if you really want some useful empirical formulae then go tell your library to get you a copy of the SAE R-161 textbook (or buy it!!!) and there are all the formulae you will need to help you make these big decisions on 2st exhaust pipes before you wield your hacksaw. They are much too extensive space-wise for me to repeat them here but they are quite usable to anyone with a calculator. (also, and tongue-in-cheek, there is only one 'f' in Professor and I will NOT be replying to the inevitable smart comments which this spelling correction will produce!)


Posted by: 2strok4fun

Spelling has never been my stron point. I have given up long ago. And if my keyboard typed like I write, it would all be illegible. I am a long way from proffesor, let alone profesor.

I have checked the local library for some other SAE papers with little success, I think purchase of R-161 is in order. The SAE web site has it available? Amazon list it as out of print I think.


Posted by: gblair

to 2strok4fun...

..I am surprised that Amazon has it so listed...but I did notice that they have done that before if they run out of stock...yet still have it!

I can assure you it is not out of print...and SAE will sell you a copy of the R-161 book for sure.


Posted by: gblair

to 2strok4fun..

..you can go straight to it on the SAE web site by going into mine (www.profblairandassociates.com) and clicking directly on the book name as you come across it..that is a direct link to the book and its software companions) (same approach for the R-186 4-stroke book)


Posted by: gblair

...to all..

...all silence in here since 1st February..I think I'll go for a holiday!


Posted by: 2strok4fun

Well I have some serious homework to do before I can post anymore questions or comments


Posted by: steve125

Professor Blair, in a case reed design motor, unlike a piston port reed design, it's rear boost port is a tunnel up from the cases similar to the main transfer ducts but much narrower. In order for a boost port in the back of the piston to feed this kind of port it must access the rear transfer window itself, at just before and just after BDC. This port window extends down past the other transfer windows and allows for this passage from the pistons boost port. In regard to the trapped mixture that is under the piston crown and being delivered through an opening in the piston at the port window itself, would the flow here disrupt the main tunnel flow up from the cases and not be a preferred access because of this? Also at what speed range would you feel this boost port would be most helpful if it is at all? Thanks Steve!


Posted by: gblair

..to 2strok4fun..

..true, I forgot you have a lot of reading to do...and a stiff class test on it to follow for you when you are done...!


Posted by: gblair

..to Steve125..

..it has long been held that an access window to a rear (or any) transfer port does little to disrupt a flow process and under most design circumstances will actually aid it but, more importantly provides a flow path for air and fuel and oil to, past, and on to the small end bearing thereby improving its lubrication characteristics. As the small end bearing in a 2st engine is always loaded in one direction (unlike a 4st engine which unloads at tdc on valve overlap) this is extra lubrication path is always welcome.


Posted by: gblair

to Steve125..

.and, I forgot to add, the fresh charge flow through the piston window into the rear transfer port also provides extra under-piston cooling. That, too, never goes amiss.


Posted by: 2strok4fun

Professor Blair, On the subject of piston cooling and small end bearing wear:
Has there been any testing or data using piston crown treatments such as THIS LINK ?
If it reflects more heat back to the combustion chamber, there would be less heat transferred to the piston, therefore transferring less heat to the piston and the charge under the piston. Could this improve VE or help with small end bearing wear by keeping it cooler? I would assume that if it worked it would provide the most benefit to extended full throttle applications such as karting and watercraft.

I am getting SAE R-161 as a early birthday preasent. Ill let you know when I get it so you can give the first Quiz.


Posted by: steve125

Professor Blair thanks so much for answering! My last question on boost porting is kind of a lead up to this important question. Some piston manufacturers are giving  tuners a choice and that is with or without the boost port machined into the rear of the piston. They claim a better low end power with the windowless piston design (case reed motor). Is this possible? I have a theory on how this could be possible but I would rather not guess. Can you shed some light on this??.........thanks Steve..............Marcus are you happy now? :thumb:


Posted by: marcusgunby

Steve the KX is alive and the weathers looking better-good enough reasons to be happy


Posted by: gblair

to 2strok4fun...

..what is THIS LINK..and what is VE? Piston crown treatments so far have not been universally successful but that does not mean that there is not a new a super material out there that I do not know about and will be able to stick permanently to the piston (and not be abraded by knocking). If it does AND has a low thermal conductivity (no good if it does not) then that will do all of the good things you talk about.


Posted by: gblair

to Steve125...

..if they can prove that this is the case (the windowless piston is better) then I will acccept that but it does also say that there is a flaw elsewhere in the design as that should not be the case if all else was optimised.


Posted by: 2strok4fun

Sorry Professor Blair-
:o
The link is www.swaintech.com/race.html

I abreviated Volumetric Efeciency to VE.

Thank you,

Chris


Posted by: motometal

so, after removing the "masking" or "shrouding" around the valves on my XR650 head, I read this thread. Bummer!

Please explain more about how the factory "shrouding" aids low lift flow. It just looked to me like it was in the path of the flow, but I had a sneaking suspicion I shouldn't grind it away...

hopefully the gains from the smoothing under the vavle seats will counteract the damage I did...


Posted by: Rich Rohrich

Quote:
Originally posted by motometal

Please explain more about how the factory "shrouding" aids low lift flow. It just looked to me like it was in the path of the flow, but I had a sneaking suspicion I shouldn't grind it away...


motometal - take a look at the shape of the valve seat from the throat to the chamber and you'll see how the chamber cuts help to form the wide end of a divergent cone. The more gradually you can ease the air from the the small area of the seat to the large area of the cylinder the less flow separation you'll get as velocity is exchanged for pressure . Do it too quickly and you cut flow dramatically. It's the inverse of the concept behind using velocity stacks on carbs. It makes a HUGE difference when you do it wrong. REAL porting these days is ALL done within about an inch of either side of the valve. The rest of the nonsense people usually do in the ports amounts to nothing more than metal masturbation.


Posted by: motometal

hmmmm....i'm beginning to understand....i can also see how the stock design directs the flow towards the center of the combustion chamber (or towards the piston) instead of along the top of the chamber, this also keeps the flow from an intake valve from trying to cancel out the flow from the other intake valve.

What do I do now, put 'her together and hope for the best? Get out the welder? And here I was so proud of myself for completing the work without nicking the seats... Rich or Eric, please tell me it'll be allright, (lie if you have to) :whiner:


Posted by: LJW

Motometal,
The following link is a variation of this theme, only applied to valves.
http://www.feuling.com/tech/ifv.htm


Posted by: gblair

..to all on shrouding...

...in most cases the maximum discharge coefficient of a valve is when the valve seat sits on a flat head face giving unobstructed flow into the cylinder.....however, stronger and more directed streams to aid tumble or swirl can be aided somewhat by directing the flow by near-valve shrouding at the expense of total air flow mass delivered. So, motometal, all is OK if not improved but your only worry is the amount that you lowered the compression ratio by your grinding process and so you might care to ponder how you restore that back to the original value of clearaance volume so that you do not lose power by that factor.


Posted by: motometal

hey, thanks for the reassurance. I wish I would have cc'd the head before I started. Not a lot was ground away. What about lowered compression due to valves sitting back in the head farther after a few valve jobs? Is this enough difference to even consider? I realize it affects flow...


Posted by: Rich Rohrich

Quote:
Originally posted by motometal
Rich or Eric, please tell me it'll be allright, (lie if you have to) :whiner:


Motometal - On the older XRs I've seen regular 3-5% increases in flow pretty much across the board from .050"-.300" just from cleaning up the machined ridge that forms in the port throat near the seat insert. At low lifts < .150" I've seen similar loses when the chamber side is done wrong. Keep in mind this is testing on a static flow bench. I can't tell you exactly what that translates to in terms of real world horsepower.

If I were you I wouldn't lose sleep over it. :thumb:


Posted by: motometal

do the stock ridges in the chamber side (around the valves) have any effect at high lift?


Posted by: gblair

..to motometal ..

you could always measure the clearance volume now and compare it with the declared manufacturer's value to see how it compares...as I have no idea how much metal you removed I cannot obviously answer your question.


Posted by: Rich Rohrich

Quote:
Originally posted by motometal
do the stock ridges in the chamber side (around the valves) have any effect at high lift?



It depends on the valve head shape, valve seat shape, degree of shrouding in the general area, shape of the stock ridges, etc. So a definite MAYBE, leaning towards probably, with a touch of it depends. :thumb:


Posted by: gblair

to Mr Rohrich...

..a bit of bet-hedging, maybe?


Posted by: Rich Rohrich

Quote:
Originally posted by gblair
to Mr Rohrich...

..a bit of bet-hedging, maybe?


You know it Professor. :thumb:
I stopped worshiping solely at the altar of the flow bench LONG AGO.


Posted by: motometal

The XR650L has a bore intersecting each exhaust port, which is connected to an emissions apparatus. This bore is 7.5 mm dia. and intersects the port towards the middle, at about a 45 deg. angle, leaned towards the valve-end of the port. Most owners block this off on the outside of the cylinder (so the passage doesn't go anywhere). My question: what effect does a hole such as this have on the exhaust flow? It reminds me a bit of the "boost bottle" used on some two strokes (except it's not on the intake side). the passage would have the capability of storing a small amount of pressure during the exhaust pulse, then returning it after the valve closed, but I think this will only happen if there is enough restriction somewhere in the exhaust to create the pressure.

This could easilly be plugged with epoxy to return things to normal, or maybe it has little effect. Any thoughts?


Posted by: gblair

..to motometal...

..at the serious risk of sounding as a pedant, is it not illegal to block off any exhaust emissions-related apparatus on an emissions-homologated machine?

...and now, sounding only as a tuner, block it off, and let any exhaust tuning characteristics (if they exist at all) work at their full capability!


Posted by: gblair

..to motometal...

..and in case I did not cover it sufficiently pedantically....block and FILL all holes right to the very face of each exhaust duct.


Posted by: jaguar

hi all
I'm new to this post but am very interested in it as I am trying to fully understand 2 stroke engine design.
Professor Blair, in light of this knowledge of water injection into the exhaust causing better mid range power, what is the advantage/disadvantage of using a carbon fiber pipe protector since the makers claim a hotter pipe aids power output?
True or not?: Small piston intake skirt ports mostly aid mid range power. Large piston intake skirt ports aid mid to high rpm power.
Since the curvature of the passageway between the reeds and the carb allows the wet/heavy air to centrifuge to the right side, do you think it may be advantageous to install vertical guide plates along this distance to keep the air/gas mixture from crowding the right side? Would the increased contact surface condense too much of the gas (from contact with the guides)?
thanks


Posted by: gblair

to jaguar..
..if one does not inject water to change the gas temperature and hence retune the pipe at a different (lower) speed then an insulated pipe will give the best power at its tuned speed and over its effective range by not losing heat energy from the pipe which would lower the magnitude of the pressure waves and the tuning effect as a consequence. This latter effect is really quite small in air-cooled pipes but if the pipe is water-cooled externally, as are some jet-ski engines, then there is a loss/change of performance as a consequence.

..your question on piston skirt ports is too general to be simple to answer..but basically the larger the ports the higher is the top end speed range power and that larger port back flows and deteriorates the airflow and hence power at lower engine speeds...(read a book! ie R161 from SAE)

..as to dividers, etc., in ports, it is dubious if these will be of much help except in very bent intake ducts and even then I doubt it.....the fuel is running like a river in all of these ports, straight or bent!


Posted by: jaguar

professor, if the air/fuel is equally filling the passageway (bent or not) then why the post saying that the right side reeds wear out faster? If that's true then the air/fuel mixture is heavy enough to experience centrifugal force at the curvature and thus crowd the outer side.

Does your statement about the piston windows allowing "backflow" apply to engines with reed valves?


Posted by: gblair

to jaguar..

...all ports, reed and all included, will back-flow if the circumstances of pressure ratio across that port reverse and then permit it.

...as to the reeds wearing out..well...maybe...but there could be many other reasons as well (like reeds being changed to a thinner section and so now strike a crankcase wall, etc.,)...and maybe the so-directed fuel also contributed to their demise...without knowing all of the circumstances it is very difficult at this range for me to draw a general conclusion from the comment you mentioned....


Posted by: jaguar

Yes I'm sure some air/fuel mixture will backflow through the reeds while they are closing but I doubt it is any more than normal due to having piston windows. Just my guesstimate though. I don't know what it would take to measure the backflow.
About tuned exhausts; I've heard of pro go-carts having a movable back cone in the expansion chamber to move with the rpm's. How much would a typical MX engine need it to move to stay "tuned" with the engines rpm? Do you think we'll ever see such an exhaust commercially available?


Posted by: gblair

to Jaguar..

..you cannot measure the amount of backflow..only calculate with a simulation like Virtual 2-stroke..

..re movable back cones..well it depends on the rpm range required but about 150 mm would make a very big difference..and no, I don't a movable cone is practical on a dirt bike, but other design variants might be possible....


Posted by: jmics19067

Quote:
Originally posted by jaguar
Yes I'm sure some air/fuel mixture will backflow through the reeds while they are closing but I doubt it is any more than normal due to having piston windows. Just my guesstimate though. I don't know what it would take to measure the backflow.
About tuned exhausts; I've heard of pro go-carts having a movable back cone in the expansion chamber to move with the rpm's. How much would a typical MX engine need it to move to stay "tuned" with the engines rpm? Do you think we'll ever see such an exhaust commercially available?


from what I understand go carts dont have movable back cones but telescoping tubes for the stinger do they can change the effective stinger length


Posted by: steve125

I wouldn't think changing the stinger length would be a very effective way to increase power. At least not to the degree a moveable rear cone would. As far as silencers go, with the core size all being the same, ive dynoed many different lenghts. The dyno always shows little or no change in the power curve. But a good test rider can feel a difference in how the power is delivered, switching from long to short silencers or the other way around.&nbsp;


Posted by: jaguar

prof Blair
since I've got your ear I'll ask another design question.
Do you think a carb with multiple "entry points" for the gas (as opposed to just one point at the middle/bottom of the carb throat) to mix with the air would be of any advantage? It would more evenly mix the gas with the air and possibly have a better degree of gas atomization. But if the gas is evenly distributed by the time it gets compressed, and the atomization is not important then of course the answer would be no. But I'd like your ideas on the subject.


Posted by: 2strok4fun

Quote:
Originally posted by gblair
...all ports, reed and all included, will back-flow if the circumstances of pressure ratio across that port reverse and then permit it.


Professor Blair, this back-flow is partly a result of blow-down time / area, are there instances of too much blow-down time /area?

I still havent gotten R-161 yet, as my wife says it is still TOO early for a early birthday present. :whiner: But I have web links pasted to my wife's computer


Posted by: jaguar

Seems like an ideal place to put metal reed valves to lessen mixing of exhaust with fresh air/gas mixture.
I always thought the CanAm bikes had a great rotary intake design. Why did that design die out?


Posted by: gblair

..to 2strk$fun...

..the exhaust port is a special case..there you want 'backflow' at the point of exhaust closing to increase the trapped charge mass by flowing lost charge from the exhaust duct back into the cylinder..that is how a 2st engine produces high power output. (you still need that book!)


Posted by: gblair

..to Jaguar...


...disk intake valves did not die out....Aprilia used them in 2st 250cc GP engines and won World Championships right to the present day.


Posted by: gblair

..to all on the subject of 'stinger length change'...

..Steve125 is quite right ...stinger length change hardly affects the power output at all..but stinger diameter is one of the most sensitive design parameters in expansion chamber design.


Posted by: gblair

..to Jaguar..

...please clarify your question ..multiple carb entry points (for a 2st or a 4st?)..which engine...

..many four-valve 4st engines have individual runners to each valve with individual EFI into each duct and many designs used 2 carburetters...but no real advantage can be discerned on power performance ...

..as to 2st engines, several designs used two carburetters with/without reed valves, but again no real advantage could be found by comparison with an equally-well-optimised single-carb set-up.


Posted by: jaguar

Prof Blair
about the multiple entry points; I was thinking how when the throttle is fully open that the gas mostly mixes with the lower half of the air stream, and so was thinking that it would be beneficial for the gas to enter the carbs air stream at multiple points instead of just one at the bottom of the throat.
You overlooked my question about the possibility of placing steel reed valves at the transfer intake ports to keep the exhaust gasses from mixing with the fresh fuel/air mixture. Good idea or not?
Also why is a big carb so important when the reed valves are so limiting?
thanks


Posted by: 2strok4fun

Professor Blair-

The back-flow I was speaking of was the back-flow of the transfer ports in relation to the blow-down time/area. In my mind, more blow-down time will reduce the pressure at the time the transfer ports open, reducing the amount of reversion and increasing the net flow through the transfer ports, and possibly increasing port velocity as well.
So to my original question. Concidering the timeing of the exhaust remained at the same degree mark, are there instances of too much blow-down time/area and what would the concequences be to seat of the pants power delivery? I am asuming the blow-down time/area can be increased by widening or shape change where allowed.

Thanks again for the education, entertainment, and distraction.


Posted by: ericlachance

Hi, I have to be honest, I've been reading posts on this board, and I don't understand a damn thing you guys are talking about... But thats not a bad thing. I've allways been obsessed by motorcycles and mecanics, but What I really like is the technical aspect of it(in otherwords, the effects of porting and fluid movement in the cylinder). I also have to say, Eric Gorr your allmost like a hero to me, but enough sucking up, what I really wanted to know is how and where do I lurn to do this kind of thing? I'll be going back to school in september(after a short break)as a student in motorcycle mecanics, but I really wanted to lurn about porting engines. Are all you guys engineers or is there an other way to lurn how to do this? Your replys are really appreciated.

Thanks
Eric


Posted by: jaguar

I'd go to amazon.com and pick up some books on the subject. such as...
The Basic Design of Two Stroke Engines by Gordon P. Blair $288
Design and Simulation of Two-Stroke Engines (R161) by Gordon P. Blair $117
Two-Stroke Performance Tuning by A. Graham Bell $28
Two-Stroke Cycle Engine: It's Development, Operation and Design (Combustion)
by John B. Heywood new_$110 used_$85

Then probably some engine simulation software such as Dynomation at http://www.audietech.com/dm2.htm

Then get a dremel and angle or flex shaft as well as an assortment of bits.

Then some engines to practice on. (friends with the promise it will be made better)

Then you can plug all the dimensions into the engine software and record the expected power output and then with each conceived change (such as raising the exhaust port 2mm) you'll be able to see how it affects the power and powerband. Then you can finally decide on the changes needed and then go to it with the dremel.


Posted by: gblair

to jaguar....

..reeds in transfer ports...the backflow rarely gets the whole way to the crankcase before the flow reverses and so a reed valve, while it may hold up that backflow will be an obstruction to the normal flow when that starts to take place...and so it is more than likely that a net loss of flow of fresh charge would be tthe outcome.

..as to big carbs (as you put it..although big is a relative word and not a numeric value)...the larger the carb the higher can be the pressure ratio across the reeds and so increase the maximum flow at the highest engine speeds but to the detriment of carburetion (air-fuel ratio control) and air-flow rate at the bottom of the engine power band.


Posted by: gblair

..to 2srk4fun...

..more exhaust blowdown time-area can increase maximum horse power but that is to the detriment of the power band as the exhaust pipe then cannot tune over the same range of engine speed and successfully 'gas-dynamically-plug' the larger exhaust port during the exhaust port closing region.


Posted by: gblair

..to ericlachance...

..read a book....and the further references within it.....see SAE book ref. R-161)


Posted by: gblair

to ericlachance..

..I wrote this reply before I read the much superior response by 'jaguar'....he says it so much better...


Posted by: 2strok4fun

Cant get anyone to do my homework these days

So let me see if I undetstand your response;
The powerband could be effectively narrowed because it woud take a stronger pulse to gas plug the larger port, that stronger pulse would only be available at the higher rpm ranges. This is even tho the exhaust timing remaind constant to pre-mod timing.

Professor Blair, Would you think that I would be able to comprehend the technical level of R-161 given my level of understanding? Or is there a entry course to R-161? How many points taken off for spelling?


Posted by: gblair

..to 2strk4fun...

...with the larger blowdown are, even at the same timing, the 'weaker' pressure plugging at the lower speed points would still give the same effect, ie a narrower power band. All of the answers of course are predicated on there being the 'correct' amount of blowdown area in the first place to produce the best possible tuning and exhaust gas dynamic plugging at the higher engine speeds in the first place!

..and, yes, I think you could benefit by reading the R161 book, irrespective of your technical background....but the better that is the more you will get out of it.


Posted by: gblair

I have just written some articles in a magazine called Race Engine Technology and the movies of the pressure diagrams and the CFD calculations within the airbox restrictor pipe are uploaded on to the www.profblairandassociates.com website as a free download to all who want them. You will find them informative on engine tuning..but you really need the Race Engine Technology articles to full understand want you are looking at.


Posted by: 2strok4fun

Professor Blair, glad to see you back. Although delayed, (my wife couldnt find my blunt hints) I finally recieved the ups delivery of your book. But it appears I will be converting my 2-strokes to hydrogen as SAE sent me R-160 by mistake

Oh well I guess I'll have to wait longer for my first quiz, spelling optional.


Posted by: JFN

I tried the Race Engine Technology web page but could not find the issues with the above mentioned articles. Issues 2 & 3 are out of stock. Is there any way to get the articles somewhere else? Or did I miss something?
I have Prof. Blair's book and software and I have some questions pertaining to the Model No 2 sim program. Since I bought the program in 1996 has there been a updated version (I'm not referring to Optimum's version)? If not is there any thing that should be changed in the GP125 spec sheet? Example: 6 deg burn delay to 10 deg. Although I must admit I use the 'Automatic' setting for the built-in empiricism because I don't have the means to check my 'BYUSER' imputs.
Another question about the scavenge models used in the program. Are all 15 YAM models in the program?
I understand all (I know I'll regret saying that later on) of the data output except one. What is the 'KTEMP' output and what are the limits I should be looking for.


Posted by: gblair

Quote:
Originally Posted by JFN
I tried the Race Engine Technology web page but could not find the issues with the above mentioned articles. Issues 2 & 3 are out of stock. Is there any way to get the articles somewhere else? Or did I miss something?
I have Prof. Blair's book and software and I have some questions pertaining to the Model No 2 sim program. Since I bought the program in 1996 has there been a updated version (I'm not referring to Optimum's version)? If not is there any thing that should be changed in the GP125 spec sheet? Example: 6 deg burn delay to 10 deg. Although I must admit I use the 'Automatic' setting for the built-in empiricism because I don't have the means to check my 'BYUSER' imputs.
Another question about the scavenge models used in the program. Are all 15 YAM models in the program?
I understand all (I know I'll regret saying that later on) of the data output except one. What is the 'KTEMP' output and what are the limits I should be looking for.


I never said the articles were on the RACE ENGINE TECHNOLOGY web site..I said the movies relating to the pictures within the articles in issues 2 and 3 of RET were on OUR website (www.profblairandassociates.com). How you get the articles if you are not a RET subscriber is a matter between you, the RET editor, and God.

There have been no updates to the 2-stroke SAE software since it was issued in 1996. It now looks very old-fashioned by comparison with that seen with the R186 4-stroke book and I am suitably ashamed of it nowadays but am too busy to do anything about it. Anyway, who would buy it, as 2-stroke engines in motorcycles seem to have been politically relegated into the mists of history.

As to advice for Ktemp look up the R161 book at p242 and see the equations relating to Ctemp (same thing) for your advice.

Nowadays in the modern VIRTUAL ENGINES 2st software the need for such a Ktemp function has been eliminated.

As to the scavenge models, then only those that are listed as accessible are actually within the R161 model software.


Posted by: JFN

Thank you very much for the reply.

Quote:
I never said the articles were on the RACE ENGINE TECHNOLOGY web site..I said the movies relating to the pictures within the articles in issues 2 and 3 of RET were on OUR website (www.profblairandassociates.com). How you get the articles if you are not a RET subscriber is a matter between you, the RET editor, and God.


I apologize for the confusion and misunderstanding about the articles. I e-mailed the RET editor to see how I can aquire them. I looked at the movies on your web site and can see how having the articles would allow me to understand alot better.
As for the 'Big Guy', I had a chat with him just last night, albeit a little one sided. And since I woke up to a beauitful day I hope it went well. Although I will have to admit that your articles never entered the conversation. So we'll have to wait and see.


Quote:
There have been no updates to the 2-stroke SAE software since it was issued in 1996. It now looks very old-fashioned by comparison with that seen with the R186 4-stroke book and I am suitably ashamed of it nowadays but am too busy to do anything about it. Anyway, who would buy it, as 2-stroke engines in motorcycles seem to have been politically relegated into the mists of history


Too bad about the updates, and I really don't care how old fashioned they look. I have many wins and a National Class Championship in the GNCC with motors as a direct result of using your book and software and sim program. And to tell you the truth I hope nobody else buys the program, I haven't won my share yet. And who wants to be politically correct anyway?

I understand about the 'Ktemp' and the scavenge models. Again thank you.


Posted by: Lazyeiger

Prof Blair,

The 2004 rules for our karting organisation have introduced a mandatory airbox rule for all karts, even though the airbox is not allowed to be modified this got me thinking about airbox dynamics. It has been said that this particular airbox was designed for use with a KT100 fixed gear kart engine and that an improvement in engine performance is seen when using it. We are forced to run this box on a 125cc 6 gear kart engine (CR125 in our case) and we suffer a noticable decrease in performance.

Does the airbox perform more like a fixed resonant cavity, which may help by stuffing the intake at resonance? Or does it behave more like an exhaust pipe whith sound waves where a cone arangement could be made to work over a wider frequency range? How would just increasing the length (volume) between the box and carb effect the performance?


Posted by: JFN

Lazyeiger;
Is your karting org using the air-box for noise restriction (what an air-box is designed for) or as a means to restrict or cut back on power (usually due to some insurance co complaining). Do they call the class 'Baby NASCAR'? Just think what they would do if you ran spoilers.


Posted by: Lazyeiger

Quote:
Originally Posted by JFN
Lazying;
Is your Karting org using the air-box for noise restriction (what an air-box is designed for) or as a means to restrict or cut back on power (usually due to some insurance co complaining). Do they call the class 'Baby NASCAR'? Just think what they would do if you ran spoilers.


JFN, completely for noise restriction, which by the way I totally agree with!


Posted by: 2strok4fun

anyone running the 2-stroke software on Windows XP machines. I just got my new laptop and home computers updated, I havent tried the 2-stroke on the new machines yet, but other DOS ones that I have tried didnt work.

Guess I could keep my o'l 98se in the shop runnin.

Hmmm, what does 2-strokes and DOS have in common. They are both almost extinct and I am just starting to learn it.


Posted by: marcusgunby

Suzuki have just learnt how to make a good 2 stroke engine just as sales of the 2 strokes are almost nothing.


Posted by: Lazyeiger

OK, I think I have figured out that the airbox is just a "simple" resonator, now the question is should it be tuned to the same or double the piston frequency at peak torque???? also I am not sure how to deal with the resonance frequency math for multiple tubes???


Posted by: JFN

Lazyeiger;
Blair's book has a complete chapter of silencers and how to build them for both exhaust and intake. He explains it all.


Posted by: gblair

Quote:
Originally Posted by Lazyeiger
Prof Blair,

The 2004 rules for our karting organisation have introduced a mandatory airbox rule for all karts, even though the airbox is not allowed to be modified this got me thinking about airbox dynamics. It has been said that this particular airbox was designed for use with a KT100 fixed gear kart engine and that an improvement in engine performance is seen when using it. We are forced to run this box on a 125cc 6 gear kart engine (CR125 in our case) and we suffer a noticable decrease in performance.

Does the airbox perform more like a fixed resonant cavity, which may help by stuffing the intake at resonance? Or does it behave more like an exhaust pipe whith sound waves where a cone arangement could be made to work over a wider frequency range? How would just increasing the length (volume) between the box and carb effect the performance?


from gblair

I don't know what this airbox looks like so I find it difficult to make a comment. What does it look like, what are its dimensions including volume and what does the intake pipe from the atmosphere look like and what are its dimensions (length and diameter) and what is the carburetter flow diameter?


Posted by: Lazyeiger

The airbox volume is 3500cc it has 3 inlet tubes 29mm ID by 95mm long with bell mouths on the inlets but just cut square on the exit. these tubes extend into the box such that the entries are flush with the outside of the box. Carb is 38mm.


Posted by: JFN

I'm building a project engine. Bore=67mm, Stroke=55.6mm, twin cyl, peak RPM=10,750-11,000. This engine is similar to the old Yamaha RD 350 except the intake is piston ported instead of reed controled. It has a single exhaust port (not bridged). To get the needed blowdown time area do I raise the exhaust timing to 204 deg duration and widen to 75% of the bore or do I add sub-exhaust ports and keep the exhaust port down to a milder state of tune? By milder I mean the exhaust port dur. at 198-199 and 70% of bore for width. The engine is for a snowmobile and will be used for dragracing. The simulation program I use shows that I will get more power with the sub-exh ports.
Any one have any thoughts on which way to go and WHY?


Posted by: imoto

Has anyone spent any time reaseraching the potential benfits of running a velocity stack on a late model 4 stroke carb (FCR)?


Posted by: Rich Rohrich

Quote:
Originally Posted by imoto
Has anyone spent any time reaseraching the potential benfits of running a velocity stack on a late model 4 stroke carb (FCR)?


Yes, there is defnintely power hiding there. :thumb:


Posted by: imoto

Hey Rich, is there any info that you can share about the "stacks" with us. I've had them on most of my roadrace bikes, but now I'm trying to hotrod my Supermoto YZF450. This is what I'm building right now... stock carb (JD kit), bluprinted head, competition valve job, 13.5:1 wiseco, M4 rerverse cone megaphone system, no-toil supermoto filter w/cut cage, 7oz flywheel. I need to get at least 57-58hp to stay competitive with the front guys.
A: Could you get the same/similar results as running a stack by taper boring the carb? Pros? Cons?
B: What do you think the minimum MON I'll need from the gas with the 13.5:1. I was planning on using Ult4, but it doesn't have a very high octane.
C: I've read about motor builders performing a "carb mod" in conjunction with their head mods. What do you think this "mod" consists of?
I noticed that on Doug Chandler's HMC KTM when I was at Stockton testing, that they run a clamp on K&N filter and no airbox, will a clamp on really flow that much more air than the airbox and filter setup? Thanks Rich!


Posted by: holeshot

Quote:
Originally Posted by EricGorr
Regarding the port edge "rounding" on plated cylinder bores a small burr forms on the port edge during the electroplating process. The electrical current arcs to any sharp edges and produces a build-up of material. During the honing process only half of the burr is removed, the part protruding into the bore. Sometimes that burr can be a real hinderance especially if its a small bore cylinder.


This kind of gets away from the porting aspect of this thread. I recently put a new piston and ring in my KX125 and a little later, I decided to examine the old ring under a magnifying glass (my near eyesight is not what it used to be). I was surprised to see that a chunk of the ring was missing, a piece about 1/2" long and a third the width (depth) of the ring in an area near the exhaust port (forming a chamfer in that area of the ring). The area of the ring under the missing piece is not marked at all, so I doubt if the power valve is making contact, but more likely that the ring caught an edge. If I'd sprung for one those digi-cams, I'd have a picture.

Could this be caused by the burr you're talking about?

BTW, no cylinder was safe from my (borrowed) dremel tool a few decades ago, but I'd prefer to leave porting to the experts now.


Posted by: hot125mod

it seems to me 100,000 rpm is way to high of a bit speed and it would tool harden the metal making it unworkable. even 30,000 rpm



This is the text version of DirtRider.Net
Click Here for the Full Version

Text Version Home





vBulletin Copyright ©2000 - 2008, Jelsoft Enterprises Limited.
vB Easy Archive Final ©2000 - 2008 - Created by Stefan "Xenon" Kaeser