what shape pistons?
Thread Starter
Instructor
Joined: Dec 2001
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what shape pistons?
I have 76cc heads 993 castings and I am looking for your advice as to what
piston tops or domes are best compressititon ratio does not scare me. I will
be happy with 12:1 or 11:1 also I have 194 intake 150 exhaust what about
194 intake 160 exhaust any benifet
piston tops or domes are best compressititon ratio does not scare me. I will
be happy with 12:1 or 11:1 also I have 194 intake 150 exhaust what about
194 intake 160 exhaust any benifet
Le Mans Master
Joined: Aug 2000
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From: Semper ubi, sub ubi
Cruise-In VI Veteran
Cruise-In VII Veteran
Re: what shape pistons? (mountainshark76)
I think that with those 76cc heads you'll have a hard time getting 12-1. The pistons would have to be very steeply domed, and valve clearance would be critical. I think you'd be better off with a better set of heads with a smaller combustion chamber.
Le Mans Master
Joined: Sep 2001
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From: Unreconstructed, South Carolina
Re: what shape pistons? (mountainshark76)
Agree w/ smokehouse. Also, domed (popup) pistons are old school ... pretty much obsolete for sbc. Proper quench (say 0.030”- 0.040”) along w/ smaller chambered heads w/ flat tops or dished is proven most efficient for 23º sbc heads. Here’s a no BS example: with small valve iron GM heads much like yours (ours milled to make ~70cc chambers), 4.030” x 3.48” zero-decked 350 block, 5.7” rod, FLAT TOPS with minus-2cc, 0.020” thick gasket, max .480” lift @ valve solid flat tappet cam, roller rockers and a Two repeat TWO barrel carb feeding RACE GAS ... we’re making about 10.5:1 static CR and getting 370-plus HP from our local late model stock circle track motors ... NO BS. I’ve seen a bunch of competitors torn down for tech (ours too) ... everyone’s running same configuration piston-chamber. BTW, small stock-type elastomer-rubber dampers (not big$ fluid) are the norm ... no damper/snout/crank probs. Forget popups ... go flat top with a thin gasket /milled heads.
PS ... whether you make it to 11 or 12:1 CR or not ... your CR should be an important consideration.
