4 mill coolhead domes question

[thomas h.]

My compression at sea level is 110 lbs. Not sure what domes a have. But are 4mill cool head domes cut just for this crank or can I just by any dome size I want?

Second question will 145 lbs compression work running 91 octane?

Thanks Thomas.

[AKheathen]

My compression at sea level is 110 lbs. Not sure what domes a have. But are 4mill cool head domes cut just for this crank or can I just by any dome size I want?

Second question will 145 lbs compression work running 91 octane?

Thanks Thomas.

well, if that's your compression, then either you have some huge domes, large sqush clearance, or allot of porting. i would check your squish first, and make sure that your tester has the shrade valve in the verry tip, and as long as the spark plug. do you have a metal spacer under the cylinders? make sure you need to have recessed domes first. if you have a good squish (.060-.040, iirc) then, yes, you need to run the same type of domes that are clearanced for the extra stroke. typically, you can go higher than 145 on 91, but that should be fine. remember, if you are going off the dome size chart to figure your compression, then you have to factor in the extra 4mm of stroke, which does change the compression allot.