Squish band? on a 250 nc m3

[Eldert]

dont go to small on the on the squish . for a narrowcase with stock rod and heavy Borgo piston ( 405 gram )
i would say 0.050 is the bare minimum . keep in mind guys we take the measuments static .
when the engine is running full blast the crankshaft flexes , the rod stretches and so on

i set up racing 250 engines so tight on the squish that there was no carbon build up in that area

with a good quality racing rod and a light racing piston ( 335 /360 grams ) you can get away with less squish

if you go to small on the squish the piston wil hit the cilinderhead and the top pistonring will not move freely in its groove
so power is lost.

bevel bob , if you wanne improve performance on the 250 raise the compression ratio with a racing piston
the stock 10 to 1 Borgo has only a little over 9 to 1 compressio ratio .
get it up to 10.5 to 1 and you can go 1 tooth bigger on the front sprocket
relocate the spark plug ( a small 10 mm one ) or add a second plug to aid combustion

Eldert

[Bevel bob]

thanks Eldert,I think you are right,my 175 had a CR of close to 11 to one and would leave my current 250 .I was thinking of about 10 to one with a second plug to allow reduced timing .It is always going to be a fussy demanding beast but thats the fun in it.

[jbcollier]

15 thou is not enough. Please do not go absolutely any smaller than 30 thou. I use 0.8 mm (.030ish) to 1 mm (39 thou) myself.

[Bevel bob]

Thanks all, the motor has to come down to stop the gearbox leak ( my bad work!) so there is an opportunity to experiment.