Quote:
Originally Posted by "QUICK-SILVER"
Stan,
Cranking compression for 69' 400's factory rated at 10.75 CR, was 185-210.
Guessing low number was for 041 cammed engines and high number for 068 or 067?
OP's 278° cam with 105° ICL has got to be adding to effective stroke and running the cranking compression up.
Don't remember now but did the math in my head when you recommened the 068 cam for this. Big difference in intake close between it and whats being used.
Clay
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I tried a little math years ago, and figured out that factory CR ratings were based on a zero deck, zero valve relief, and an exact match to chamber volume as blueprints, and maybe even no head gasket.
The one thing about factory ratings, even if their claimed 10.75:1 was really 9.25:1(or whatever) they still recommended the fuel of the day, which was 98 to 104 octane, and I think octane ratings changed on the pumps, where now it is an average of two ratings. You can't really compare CR going off factory ratings to run today's fuel.