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latest magazine mystery statement
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Posted by: lawman

this is not about why my brand doesn't win all the shootouts; it's about a puzzling (to me) statement in the latest edition of dirt bike mag. no, not the 1 where they say "...the 4-stroke revolution has all but taken over the full-sized dirt bike world" (p.40), when just a few months ago they claimed that all the big off-road races are still won by 2-strokes (both are overstatements, imo). & it's not the unsupported allegation that "the AMA is definitely chock-full of politicians who treat their own members as adversaries while sucking up to the true enemies of our sport--dianne feinstein, barbara boxer and ted kennedy" (p.18). that's a very serious charge to make in an offhand, unsupported comment, i think.

no, it's about this sentence: "too, the factory fatty has additional midrange torque over the fmf fatty and sst since it has the same 20 lighter gauge (thinner material) metal body that all of the factory teams race with." (p.59) hunh? what? setting aside the awful sentence structure, what i want to know is this: the thickness of the steel in the pipe affects the powerband of the bike? do what? are there any metallurgists/engineers in the house?

Posted by: bwalker

Psuedo science IMO.

Posted by: 2strok4fun

The only way I could see that to have an affect on power delivery would have to be what the thinner steel would do to pipe temp. If the steel is thinner it could loose more temp to the surrounding air and cool the gas temp inside the pipe, the cooler pipe would act longer moving the torque lower in the rpm range. Whether or not it actually does it or not, I certainly cant comment. But I think that the pipe would also be more vunerable / tempermental to outside temp changes.

Idunno. WAG

Posted by: luvtolean

I am just lobbing a shot in the dark here, but the thinner material will also change the resonant frequency of the pipe as well as having different damping effects on the pressure waves in the pipe. No idea how these things might effect the power.

I'm an engineer, but this isn't my field.

Sounds like the mag took the propaganda speak from some FMF marketing tool.

Posted by: MX175

I agree with the above. As a metallurgical engineer, my first reaction was possible variations in the resonant frequency and damping effects. But the temperature theory makes some sense too. My fear of the pipe may be its tendency to dent more easily from spills (not me) and roost (unless your leading the race).

I rode, and read, a lot in the mid 70's to the mid 80's, and have just gotten back to dirt bikes in the last 6 months. I am very disappointed in the qualityof the magazines. In the 70's Dirt Bike ruled. It was great to get the straight scoop without the hidden inuendo. In the current magazines, if they have to say anything bad, they hide it around lots of good points. Dirt Bike's headline for the Honda SL125 (in the 70's) was "Turtle Chaser". No hidden meaning there. Bring back Super Hunky...Sorry, to get off the track here but I needed to vent a little.

Mark
'80 KDX175
'85 KDX200
'88 KDX200
'81 XS850 Special

Posted by: EricGorr

I've heard a lot of theories about pipe materials regarding heat transfer, maintaining the energy of the waves and such. We've seen materials ranging from mild steel, stainless steel, titanium, carbon fiber, and aluminum. Seems like everytime a new material is flaunted on the market theres an outrageous claim of "5 more hp" or "more of everything".
The only theory I can find truth in is that pipes are bumpers for dirt bikes. Dirt bike pipes are such a compromise of design. They're contorted to fit such an obscure space definition. Riders whine about "it cases whoops" "it burns my pretty white boots" "it rusts" "it gets dented too easy". If a manufacturer really wanted to make a pipe that actually helped performance, they'd step back to the early 1970s when pipes were like hippies. Low slung and unencumbered by white mx boots and big bumps. Remember the old TM400? There was a classic pipe that was actually the right length, sort of a fundamental design aspect of a 2 stroke exhaust system.

Oh no I'm getting a vision! I picture a group of marketing guys from a big aftermarket exhaust manufacturer reading this chanting "Hippy Pipes" EXCELLENT!

Fast forward to the future issue of Dirt Bike Action "Our wrecking crew experienced a 20% increase in euphoria when racing with a Hippy Pipe. If the 2003 KX250 had a Hippy Pipe, it would of won our shootout hands down".

Posted by: Studboy

LOL. Excellent...could we get it powdercoated in psychadelic rainbow colors? That would boost performance......yeah I love that. "This bike can be transformed into a screamer with a FMF pipe on it!".

Posted by: 2strok4fun

Quote:

Originally posted by EricGorr
The only theory I can find truth in is that pipes are bumpers for dirt bikes.

Well thats how mine get used.

Posted by: jmics19067

If you used the same dies to stamp out different thicknesses of sheet metal could that have an effect on it? would the finish pipe have slightly different shape to it since the different thickness would not respond to the die the same way ?

if outside temps affected pipes temps thru different gauges would pipes made out of aluminum or copper have the possibility of a better performing pipe ?

Posted by: nephron

The bigger issue is the complete absence of technical material in any of these magazines. If you look at auto mags like Drag Racing USA or Drag Racing Action, eg, (and even Hot Rod and the like) there are entire sections with several articles covering technical issues. I'm not sure why the dirt bike mags haven't done this--possibly because the standard reader is a teenager with no interest in "why" things work, but only in "what" works.

It's really ridiculous. I'm sick of even seeing the words "Secret world of..." We need detailed tech articles/sections. I really would like to see in depth stuff on race fuel, exhaust design, suspension technology, etc. written in real terminology and completely objective.

What are the chances of that ever happening? :silly:

Posted by: jmics19067

Ahhh I see your point. true true ever since Rick Siemen got into a corporate stranglehold the integrity of moto journalism went down hill rather quickly. I used to love the "HOW" to make your bike survive,faster,handle type of articles compared to the how to take a second mortgage out so I can buy titanium and polished fancies so my bike looks pretty in the garage we get nowadays.

Posted by: Vic

Quote:

Originally posted by nephron

What are the chances of that ever happening? :silly:

http://www.raceworx.com/funnypics/flying%20pig.gif

Could happen any time, now.

Posted by: Rich Rohrich

Quote:

Originally posted by nephron
I'm sick of even seeing the words "Secret world of..." We need detailed tech articles/sections. I really would like to see in depth stuff on race fuel, exhaust design, suspension technology, etc. written in real terminology and completely objective.

What are the chances of that ever happening? :silly:

I guess that's why there will always be a need for DRN. :thumb:

As to the materials question. My SERIOUSLY limited knowledge of the thermodynamics of heat transfer tells me a couple of things:

- Mild steel has a thermal conductivity about three times greater than stainless steel like 304. SOOOOOOO ... if you want to effect a major change in heat transfer changing the base material from say 1010 carbon mild steel to stainless will have a greater influence on the thermal conductivity than a change from 16 to 20 gage steel

- Changing the internal temps will change the pipe tuning, but the thermal effects of pipe tuning aren't as cut and dry as these magazine guys want you to believe (see referenced paper for some REAL details).
It's much easier to "hint" at a magic effect than it is to PROVE IT. Typical half-assed butt dyno BS from these TECHNO-CLODS.

- "factory" guys strive for the lightest parts possible, even if that means tossing parts at regular intervals. Thinner steel is lighter. See a pattern here?

It's pretty clear that this is nothing but a thinly disguised press release. As Eric pointed out, thin pipes will get damaged easier and need to be replaced more often. Most people understand that. BUT, if people perceive there is some magic in the thin pipe then they may be willing to endure the costs.

Seems pretty sleazy to me.

References :

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: cujet

It has always been my opinion that thicker material transfered heat faster.

Chris

Posted by: luvtolean

Quote:

Originally posted by 2strok4fun

Well thats how mine get used.

:D Mine too, that's why I won't get rid of the stocker until it's fully caved in.:P

Quote:

Originally posted by cujet
It has always been my opinion that thicker material transfered heat faster.

Chris

Nope. A thicker material is a better reservoir of heat (or lack of) but it will slow conducting/convecting/radiating heat out of the material. You can look at the thickness of the heat as an electrical resistor(which impedes electrical flow), and the volume of of the material as a capacitor (which stores electrical energy).

Posted by: 2strok4fun

I tend to think that the average temp inside the pipe is going to be more a result of rich / lean variations at different throttl positions over the different thickness or material of the pipe itself.

Posted by: luvtolean

Quote:

Originally posted by Rich Rohrich

- Mild steel has a thermal conductivity about three times greater than stainless steel like 304. SOOOOOOO ... if you want to effect a major change in heat transfer changing the base material from say 1010 carbon mild steel to stainless will have a greater influence on the thermal conductivity than a change from 16 to 20 gage steel

Yep, you could do that or go to a couple of the hot rodder standbys, Thermotec wrap or Jet Hot coatings which are used to keep heat in the exhaust flow. Even better goto Ti. Of course, using the magazine guy's logic(oxymoron?), you'd want to get the heat out quicker so....maybe go from mild steel to aluminum?

For reference here are a couple thermal conductivities in W/(m-K). (A higher number tranfers heat better)

AISI 1010 steel 63.9
2024-T6 Aluminum 177
Pure Aluminum 237
Titanium 21.9

The factory guys use Ti expansion chambers right? (They looked rainbowed looking at them at the SF SX) If they are using Ti, they don't want to get the heat out...

Posted by: luvtolean

Oops, didn't put up Stainless.

AISI 304 14.9 W/(m-K)

All properties at 300K, important as materials aren't linear with respect to temp.

At higher temps Stainless and Ti are about equal.

400K Ti is 20.4, 304 is 16.6
600K Ti is 19.4, 304 is 19.8

Posted by: Barbarian

I think maybe part of the reason there is less technical stuff now is that the bikes are good enough stock to be raced now and there is not as much to be gained from technical
know-how as there once was. Back then you needed to be a really good mechanic just to keep a stock bike running. You almost needed to be an engineer to understand and implement all of the modifications that were being performed.
Today, you just need to be able to understand a little jetting and suspension theory to be competitive (bike wise) in most amature racing.

Posted by: flynbryan

Basically the concept is to treat the current crop of riders like a mushroom. Keep them in the dark(uninformed) and feed them crap(unsupported jargan that SUPPOSEDLY boosts horsepower and makes them LOOK JUST LIKE MIKE METZGER when hes pullin those cool backflips) Just tell them RC or Pastrana run it and its GOT TO make their bike faster!!

Please......Very rarely do I buy something unless it either breaks or I hear from first hand experience whether or not its really an improvement. Save your money for maintinance parts, your Going to need that oil filter or clutch plate set. You can still ride w/out your Fully Titanium 7hrp. gain Nathan Ramsey exhaust :silly:

Posted by: MikeT

Quote:

Originally posted by EricGorr
Remember the old TM400? There was a classic pipe that was actually the right length, sort of a fundamental design aspect of a 2 stroke exhaust system.

You mean like THIS?

Posted by: Sean Hilbert

From my experience on the track and on the dyno:

Pipe material and thickness does make a difference. There is a lot of transient behavior in each cycle of a two-stroke (gas dynamics, short circuiting, etc.), and over time (changes in engine load and RPM), and as many have pointed out, the thickness of the pipe will affect the gas temperature (and thus the speed of sound) within the pipe. This effect is manifested in the "thermal inertia" of the pipe -- i.e. heavier walls require more energy (and thus more time) from the hot exhaust gasses to heat them up.

Example: You are near full throttle going down a long back straight, and you chop the throttle going into the turn. Chopping the throttle causes some misfires and raw fuel ends up short-circuiting into your exhaust system. This cools the pipe down, and as you roll on the throttle for the next straightaway, your pipe tuning is different than it was going down the back stretch. A thinner pipe will cool off more from the raw fuel, thus giving you a little more bottom end.

Is this a big effect? It's probably not noticeable by 95% of the dirt bikers out there (we do see an effect when looking at PI data from karts, however).

So...after all that gobbledygook, why might a 20ga. pipe work better than a 19ga. one? Simple...Prototype pipes are a lot easier to make out of thinner material. The particular pipe in question was more than likely developed with the thin stuff, so that's where it performs better :thumb:

Posted by: luvtolean

Thanks Sean.:thumb;

Posted by: Fark

Quote:

Originally posted by MikeT
You mean like THIS?

 

That is cool.  I'd like to see something akin to that on a newer bike.  These things aren't that packaging nightmare that streetbikes are.  Can't someone find a design that works and is out of the way?

Posted by: lawman

thanks for the replies. sounds to me like there may be some miniscule effect, but the only place it is detectable is on the "special dyno" that is kept in fmf's marketing department.

Posted by: 2strok4fun

lawman-

While we may have come to a consensus that there may be a small difference between the 2 pipes, that dosent change the point of your original post. The mag statement without ANY facts could just as easily read:

"The factory pipe produces more torque because they were eating peanut butter and jelly sandwiches during welding"

Posted by: techman

Rich, the one and only time I ventured into designing a two stroke pipe (single pipe for an RD350) under the guidance of a more knowledgeable fellow, he said that the tuning of the pipe actually pulled mixture out the exhaust port and stuffed it back inside with the pressure pulse. The amount of mixture making this out and in at any set of conditions ought to affect gas temperatures somewhat. I recall estimating gas temperatures, wave speeds etc during the design. Silencer? What silencer??? All you need is a stinger! (times were different)

Getting into memories mode, I also met a 70-something year old guy with an early 1950's boat racing engine (he still raced) for which he had made a sliding center section tuned pipe out in his farm workshop. It I'm guessing a 20 to 30 hp twin. Bear in mind that steady hp in a boat is a lot harder on an engine than short blips in a typical land application. He would field test this rig, shifting the pipe around prior to a run, then reaching out and playing with the high and low speed mixture screws on his carb on the fly till it "ran good" as he put it. BTW he kicked all our 20-something year old butts.

Speaking of magazines, is my recollection correct that the TM400 has been referred to by Mr. Sieman as the "evil Toomlooki 400, capable of hurting any rider regardless of skill level"? Kind of like a DT400 on steroids?

Posted by: jmics19067

Ugh I hate when I do that, anyway from I understand and recolect from Rick Siemen's evaluation of the tm 400 was that the ignition was most of the problem on that bike. All of the hard parts on that bike was very aggresive for that time <porting,pipe etc....> but the timing had a severe advance curve to it. Supposedly at low rpm and kicking speed the timing was severely retarded to make it easy to start and putt around on. Then when you got on the gas and raised rpms all of a sudden the timing got aggresive to match the rest of the bike making for a very potent and violent hit of power when all variables lined up right.

I remember my 74 TM 250 with a smashed pipe was nothing like that.<them old down swept pipes where certainly lousy for log crossings> I had that pipe so closed off in the midsection that at idle and slight throttle the bike had amazing amounts of torque. You could lug the engine down in 3rd - 4th gear crack the throttle and the front wheel would easily come off the ground about a foot, then at about half throttle the thing just died like someone threw an anchor overboard.

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

latest magazine mystery statement

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This is the text version of DirtRider.Net
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This is the text version of DirtRider.Net
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