S3 Race 250 Port Matched Cylinder and Head

[GMP]

For a '10, I'd just pick up anything used and mod it as an experiment. Just a slightly larger core tube. I'll measure it tomorrow. I'd like to see if someone else thinks it makes a difference.


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[Neil E.]

It might be the core diameter, but I'll bet it has more to do with the Stealth insides. I just repacked mine and it's best to drill out the rivets. There is a second section of packing (~1.75" long) at the arrestor section that stays in place if you only disassemble the Stealth by using the front end screws.

The exhaust does a complete reversal after passing over the Krizman bullet. It moves out to the outside of the end cap and has to reverse direction to come back forward to get into the smaller exit tube welded to the end cap hole. The tubes overlap by at least an inch.

I think the lack of this reversal is what makes the big difference in using a different muffler.

[GMP]

I see, never had mine apart. Also explains why its an oil tanker. All I can say for sure is its definately not the best choice. I have an '07 250 with a Messico silencer, otherwise set up the same as the '12. It was always the low/mid champ until the Cannon went on the '12.

Seeing that I'd mod it for sure if a replacement was not in the plan.

[Neil E.]

As to the best mod, I'd say that simply cutting out (or radically shortening) the smaller exit tube would be all that's necesssary to let the Stealth flow well. The long front perforated tube is about 1.125" diameter and the orifices through the bullet are reasonable. With this mod the end cap would "catch" the gas flow off the bullet.

Rear view of bullet:

[Jakobi]

The TC2 has the same looking turbine thing when you look down the guts of it. I haven't had it apart so can't comment on the rest.

[GMP]

That's a Krizman type spark arrestor. Many mufflers use it. That in itself is not a bad thing, TC2s work fine, as did the KTM OEM silencers that used these for years. Only bad thing is that the fine oil mist in the exhaust is stopped by the bullet to an extent, and builds up in the end cap and packing.


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[kiwia]

Congratulations Jakobi, it is one of the best post I have ever seen.
Regarding S3 I have put on my 300 2010. I have put the red insert and my problem is that I can not get a good engine idle. I have proof many settings but no way. I have 3 cilinder gasket.
I want to proof 3 cilinder gasket and black insert S3 is any damage for the engine? Maybe too much, what do you suggest?

[Jakobi]

Originally Posted by kiwia

Congratulations Jakobi, it is one of the best post I have ever seen.
Regarding S3 I have put on my 300 2010. I have put the red insert and my problem is that I can not get a good engine idle. I have proof many settings but no way. I have 3 cilinder gasket.
I want to proof 3 cilinder gasket and black insert S3 is any damage for the engine? Maybe too much, what do you suggest?

Have you measured your squish height with the red insert? If you're not sure how see below.
http://www.gasgasrider.org/html/measuring_squish.html

Also could you confirm, are you running as a 300cc or 250cc? Which model carb? AS1 or AS2? Even with a largish squish you should have no issues setting up the idle and its probably more a jetting issue than an engine issue.

Trev, Lectron man? What jetting specs did you end up with on the PWK?

[kiwia]

My 300 2010 use a ASII. I am going to check the squish, but you say that even a large one does not do any problem.
I am running now with 48/178 NECJ on 2?. What do you think? It will be too much if I try black insert S3?

[Jakobi]

Which country? Temps? Altitude? Initially I'm thinking thats a big pilot, and probably a size or two larger on the main than I'd suggest (comparing to my own experiences though).

Engine wise, measure the squish with the red insert, and then measure it again with the black. They are both the same volume and its just the height that varies. I ran the black insert with my stock engine and a base gasket stack of 1.3mm which gave me around 1.8/1.9mm squish height (from memory) and 13.something:1 CR. Bike ran well.