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Old 06-09-2005, 12:57 PM
454C10 454C10 is offline
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No, 10.25:1 is not too much if the cam your use is over 240 degrees duration at 0.050". However, it would be too much if you plan on using a smaller cam. And I think you should use a smaller cam if this is going into a truck with 3.73 gears. Like I wrote earlier, a cam between 220 and 226 duration at 0.050 would be about right.

That "9.5:1 cr using iron heads with pump gas " is a VERY general guideline and depends greatly on the valve events (cam). A super simplified guideline for the novice engine builder.

I have a 11.0:1 350 sbc engine with iron heads that runs great on pump gas without the need of any timing retard because the cam is large enough to bleed off cylinder pressure (late intake valve closing point).

On the other hand, I have a 9.0:1 cr 454 that will detonate if I turn the timing past 40 degrees even with 93 octane. The reason is because the engine makes a lot of cylinder pressure from a short duration camshaft.

Both engine produce about 180 psi on the compression gage. Don't confuse cylinder pressure with compression ratio.

So, you should figure out the dynamic compression ratio, which uses the static compression ratio and the valve timing events. Buy a how to modify a sbc book and you can read it for yourself.

FYI, when buying pistons, the cc of the head should be listed along with the compression ratio of the piston.
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