bmillington

Knowing I have a stock bottom end 350, and aftermarket heads. Can I figure out the compression ratio without taking the heads off and CC-ing them. Compression test gave 180psi, and the engine dosent show signs of wear but has 140K miles. The heads spec sheet say 64cc but not sure how accurate every head is to the specs.

or

What is the stock deck height, bore, and stroke? Whats the stock pistons volume or are they flat? How thick is the head gasket. Is there a site with all this info?
Thanks,

86z28nos

Its real hard to say with out knowing your cam and piston size just a guess should be around 9.5 to 1 hope this helps

raul.garcia

Try a search for "compression calculator", you'll need to know bore diameter, gasket thickness, etc...

Compression readings aren't used to calculate the compression ratio.

Damon

An old "rule of thumb" is to divide the compression readings by 19. This is only for the most rough of estimates and not to be used as a definitive answer. However, if you have a modest cam (not some big lumpy sucker) and you're pushing 180 then you'll probably be right around 9.5:1. Both the old "19" trick and my personal experience tell me that's probably about right.