Thread: Compression

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I'd like to know where this fellow in the Camaro is skinnin' you, is it on the tree or at the 60 foot or 330 foot mark or the 660 or at the very top end......or is he just outpowering you everywhere? If he's skinnin' you on the bottom end, then you don't necessarily need more motor, you need more converter or more gear or a smaller diameter tire or all the above. What are you taching through the eyes?

A 489 BBC with a -21 cc pop-up piston, 121 cc combustion chamber, 0.020" piston deck height and a 0.043" gasket will produce a 9.73:1 static compression ratio. Same motor with a 0.023" gasket will produce a 10.1:1 SCR. You would want to closely check piston to valve clearance before making this change though, as mentioned by Glenn. I would want 0.100" clearance on the intake and 0.120" on the exhaust, as measured from 20 degrees before top dead center to 20 degrees after top dead center at overlap.

Do you know the piston deck height and the block deck height of your motor? Where does max torque occur? Where does max hp occur?

BOTTOM LINE: The aluminum heads will not like a steel shim head gasket, that's why AFR recommends a thicker composition gasket, to prevent fretting the aluminum material.
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