Hello all,
I have a 890 bird with a 305, supercharged, accel super ram and gen vii computer. the crank broke so its time to upgrade, i just had lots of work done to the heads to match my cam. Anyways if I put 350 block in what will have to do to make the comp ratio to be around 9.5:1?? Any and all comments will be greatly appreciated.
Brad
I have a 890 bird with a 305, supercharged, accel super ram and gen vii computer. the crank broke so its time to upgrade, i just had lots of work done to the heads to match my cam. Anyways if I put 350 block in what will have to do to make the comp ratio to be around 9.5:1?? Any and all comments will be greatly appreciated.
Brad
five7kid
Moderator
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May 4, 2026
Dished pistons, most likely.
You need to know the CC's of your head chambers, how far down from the deck the piston tops are, and the volume of your head gasket. Then you can pick the piston dish volume to get there.
In my case, my 305 heads turned out to have 64cc chambers. The pistons are .026" down in the bore, the head gaskets have a compressed height of .020" for a 4.1cc volume, and with 10cc dish pistons, that works out to 9.7:1 CR.
You need to know the CC's of your head chambers, how far down from the deck the piston tops are, and the volume of your head gasket. Then you can pick the piston dish volume to get there.
In my case, my 305 heads turned out to have 64cc chambers. The pistons are .026" down in the bore, the head gaskets have a compressed height of .020" for a 4.1cc volume, and with 10cc dish pistons, that works out to 9.7:1 CR.
thanks for the info
Brad
Brad