Pinging CR500 Mid/top ported by Gorr.

Mixing half and half 91 octane and 110 race gas most likely won't give you 103 octane, it is usually less than that. Try the straight race gas and then get back to us. Also check your plug after a WOT run and see if it is lean.

So, your jetting should be OK then, unless something else of the ordinary has happened like an air leak or ignition problem.

Mixing different formulas of gas together (especially pump) and expecting to calculate the octane is a guess at best.
I know that I've read a thread on this before, but I tried to find it again and I'm stumped.

91+110=201, divided by 2= 100.5. That should be fine if Eric says so. Your jetting is off, could also be rich, being excessively rich can cause detonation due to concentrated fuel pockets in the cylinder (incomplete fuel/air vaporization), creating hot spots. Get your jetting correct per the techniques in Gorr's site and in how2ride.com and you should be good. If not, then you may be running too much timing. In such case retard it a little. At least all this theory aplies to dsm turbos, figure it should work here, someone whack me upside the head if I am all wet. Good luck. :)

Also make sure the squish is correct. The CR500 needs a proper squish to reduce the detonation problems that naturally occur with the stock large clearance.

Chris

I am not sure how wet I really am. :lol: Here is some car stuff- :)

"There are several items that can cause or contribute to pre-ignition detonation. They include anything that creates higher than "normal" cylinder temperature or pressure. Advanced ignition timing, rich fuel mixture, high jacket water temperature, high boost pressure (from any form of supercharging), high compression ratio (tends to increase with increasing cylinder deposits), a too-high of valve lift (allows more air in, thus creating higher pressure during compression), etc." http://www.eng-tips.com/gviewthread.cfm/lev2/16/lev3/58/pid/816/qid/78557

I knew I didn't dream this. :)

Squish: "Turbulence generally, but not always helps to improve the homogenious nature of the mix, and in some instances it can detract from it by causing seperation of the heavy fuel from the light air dur to centrifugal force sending the fuel to the outside.

Squish also helps control detonation and propogates flame travel by greatly increasing turbulence just after ignition.

Squish or quench or whatever you call it only realy works by the piston rapidly displaceing gasses towards the combustion chamber as the piston gets very close to the head, hence the need to go as close possible without causing actual damage from impact. "

"So it looks like the consensus view is:

1. Make the squish gap as tight as possible w/o mechanical damage from contact.

2. Make the squish area as large as possible except do not exceed ~50% of bore area."

http://www.eng-tips.com/viewthread.cfm?SQID=77431&SPID=71&newpid=71&page=1

And some more-
"Start at 0.075 with an unproven combo. As the engine developed we would push toward 0.030 'ish.

Like the KZ900 example, the latest dragbike I work on is now running with light contact when using the "small motor" which is well developed. The new bigger engine is back to 0.035 just to be safe. It too will progress towards light contact.

Even with the same compression ratio, we ceratainly see power gains by getting the quench right. No doubt about it."

"The point of squish bands is to increase the mixing of the charge through increased lateral velocity. A smaller squish band gives more velocity and generally improves combustion. But keep in mind two things.

One, as you decrease the squish clearance the compression ratio goes up pretty quickly. Improvements in performance may have more to do with this than they do to tighter squish clearance by itself.

Also, I have seen situations where the piston crown and the head were parallel through the squish band creating what was in effect a ring land crevice volume. In other words the flame front couldn't travel into the squish band so the charge trapped in this area didn't burn. This not only hurt power, but also increased HC emissions. The problem was fixed by tapering this zone at about 3 degrees toward the center of the bore. This lowered the compression ratio very slightly but resulted in better power, due to improved combustion, and lower HC emissions. A greater taper - 5 deg - did not had no additional positive effect, and greater than that dropped the compression ratio enough that a power loss was noted."

"It is my understanding that a engine with large? squish areas are also less prone to detonation.In that case The slight increase in compression(and the risk of detonation)is more tolerated. This is assuming a properly designed combustion chamber. Current streetbikes are 12:1 compression ratio and tolerate 93 octane pump gas with no detonation problems..2ND.. I and slowkaw setup up engines at no less than .040 piston to head. I have tried .035 on a 1325cc Kaw., Piston was hitting the head(to hard) and fear of a crack starting between gas ports had me set it back up to .043. Absolutely the minimum for a large dragbike engine.Whats interesting is how a car drag engine can run so close a piston to head when there slinging around components twice as big and three times heavier!!As an example a JE flatop for a 1000cc motor weighs 190 grams.Very light,however max r.p.m. on this engine is a skyhigh 13000..."

"One point which no-one seems to have mentioned is that the squish area needs to be above a critical percentage of piston area to make any difference. I can't remember the exact figures but I think its around 20%. Below this figure(whatever it is) squish does not create enough turbulence to make any difference to preventing detonation. As some have observed, the improvement from having a small clearance is probably due to increased compression ratio and smaller crevice volume. So the criticism that people are too obsessed with squish is probably valid where small squish areas apply."

From- http://www.eng-tips.com/viewthread.cfm?SQID=18058&SPID=71&newpid=71&page=1

Man this stuff is cool- now if someone would just explain it to me, and confirm whether it applies to 2 smokes... :lol:

Here's the general info on 2 stroke squish bands -

If you look at the combustion chamber in your cylinder head you will see a flat spot on the outside and a bowl on the inside. This flat spot is the squish band. As the piston nears TDC, the fuel/air mixture in the squish region is squished out at a high velocity towards the bowl. This homogenizes the fuel air mixture to help promote complete and stable combustion. As an example my 2001 CR250 uses a flat top piston. The squish band is nearly flat - it is at about a 1.75 degree angle (relative to the piston). Changing the width of the squish band will have an effect on the powerband of the engine. A wider squish will give more low end power and a skinnier squish will give more top end. My CR's squish is at about 50% of the bore area. The squish clearance is the gap between the piston at TDC and the squish bands closest point (at the edge of the bore). The min squish clearance for a 250 is 1mm (.040"). In general as the displacement increases, the minimum squish clearance increases. By decreasing squish clearance to the minimum amount, you will create more horsepower because the amount of fuel/air in the squish band will be decreased. (the fuel/air displaced by this clearance decrease will contribute to more power during combustion.)

That's the basics. If you want more info read Graham Bell's book 2 stroke performance tuning or maybe somebody else will post more info.

Why is there such a misconception when it comes to reading plugs? My auto shop teacher had the plug chart on the wall that showed the insulator tips color and what caused that color.

Click to expand...

Those spark plug charts are based on research done on automotive type 4-strokes which don't use an oil mixture. Some tuning tecniques for car engines don't always directly translate to 2-stroke engines.

Steve

regarding minimum squish clearance, it sounds to me like there is additional horsepower to be had by "blueprinting" the squish clearance on a given engine, using clay or solder to measure the clearance. Since a tuner such as E.G. can't be sure of the exact clearance due to mfg. tolerances, etc., he is forced to set this clearance on the conservative side.

Am I on the right track? Maybe the tolerances of the components affecting this don't vary more than a thou. or two and the opportunity for power increase here is minimal?



Regarding the post mentioning an engine set up to have "light contact" does this mean what I think it means? Sounds like a recipe for disaster!

Yes I think it does mean that. And there is no way I would build an engine that way. Except maybe a dragster, but that's too expensive of a hobby for me!

any updates? did the pinging go away? If it were my bike, i'd be tempted to try carefully marking the current ignition timing setting, and then retarding it a bit (i'm assuming it's adjustable). On some bikes, this will support better high rpm power, and it sounds like that's what you were after. Also, there is a good chance that the pinging will go away (if it hasn't already). With a measurment and a bit of easy math, you can figure out how far to move the stator plate to give X degrees.

ahhh, I get it.

Seems like Master Rich once mentioned that even the genuine jets' flow can vary significantly (within the same number/size). Even if the hole is exactly the same, the lead in angle, chamfer, etc. may vary, which affects the flow.

Personally, i've found that moving one jet size can result in a very noticeable change or apparently no change (depending).