Squish numbers on a 310r?

[toomeysheele]

Hey there

My brother and I are trying to dial in his atc 310r motor and we're having issues. It has crazy hesitation in the upper part of the powerband. We've ruled out jetting as we've tried many different jets and they don't even touch the issue. It's the ESR cylinder with mild porting, we're kicking 150psi. I just did a squish test and got .078-.080" These numbers seem high to me. And Im just wondering if anyone knows where these motors should be..

Thanks for any help.

[ceaserthethird]

170 psi min - i would look at ESR website tech info Q&A section.

You could call them also, Great Customer Service !

[TLR-Online]

Should be around .05

From the 2-Stroke Tuners Handbook:

The clearance space between piston and cylinder head must be enough to avoid contact at high engine speeds, yet close enough to keep the mixture held there cooled during the combustion process. This vertical clearance between squish band and piston should not be greater than 0.060-inch, and it is my opinion that the minimum should be only barely enough to prevent contact -usually about 0.015-inch in small engines (with tight bearings and cylinder/rod combinations that do not grow, with heat, disproportionately) and up to about 0.045-inch in big engines.

[Racerguy381]

Im running .040 on my 250R with 200 psi on the compression

[toomeysheele]

Thanks guys,
I measured the base gasket at .040 and am thinking of using honda bond instead. It will put our squish numbers right around the sweet spot by the sounds of it.

Thanks again for the info

[Racerguy381]

Yes it will.... but it will also change your port timing... What thickness head gasket are you running? I know if you get a cool head you can set up the squish to what ever you want with a blank dome from Pro Design.