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Old 07-10-2006, 06:36 PM
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Compression concerns.

Howdy all. I am asking this question on behalf of a friend who is concerned about his compression.

He currently says he has 9.5:1 compression with his 4 valve relief pistons and 76cc L98 cast heads (for an 85 Corvette). When his engine was rebuilt, it was bored .030 over and he says the deck might have been leveled a bit. I realize such info is needed for precise compression estimations but I havent the information. I believe his headgasket thickness is around .028.

In anycase, around what compression would you say he is running currently?

Also, he has the opportunity to purchase a set of 62cc chamber Trickflows (the same heads I am currently running). He is concerned about his compression and running pump gas. Having gone from a 76cc chamber head to a 62cc chamber myself (also running flattops) I have told him that I believe he'll be fine but might have to run Plus gasoline. However I am sure it would make him more comfortable to have other peoples opinion whether they agree or disagree with mine. How much would the 62cc heads affect his compression (I have tried a few calculators and they all seem to have varying results)? And would it be an option for him to run a .051 gasket thickness to help combat compression, or do troubles arise when running that thick of a head gasket?

Thanks for your help.

Dylan.

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Old 07-10-2006, 08:10 PM
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9.8 and 11.2

made up some variables.

11.2 with the thicker gasket of coarse.

Last edited by spinn; 07-10-2006 at 08:16 PM.
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Old 07-10-2006, 10:48 PM
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Assuming it's a 350, and quench clearance ~.040", the 62cc heads would move his compression from ~9:1 to ~10.4:1.

The .051" gasket would decrease compression, but it would also increase quench clearance, which could lead to more detonation problems than before.

What cam is he running?
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Old 07-10-2006, 10:59 PM
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On both calculations, I assumed 0.010" piston to deck. I went 0.030" overbore and 0.051" head gasket (plus another 0.010" deck) with the new heads.

10:1 with a Aluminum head should be ok with premium. Of course he should check the assumptions (-5cc for the valve reliefs and 0.010 piston to deck).

http://www.virtualengine2000.com/FreeCalculator.htm



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Old 07-11-2006, 10:06 AM
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He is running a TPIS camshaft with the following specs:

224/224 @ .050 - .498/.498 lift (1.5 rockers) - 112LSA
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