How to "guess" current compression ratio

**68427** · #1 Sep 16th, 06, 10:57 AM

I have an unknown build '68 427/390. Is their any way to estimate the current compression ratio?

I already know it runs fine on pump & is relatively mild...

What I really need to know is what pistons are in it. Can the be determined mearly by removing the heads? Or can I get a hint by removing the oil pan?

I'm trying to determine if the bottom end is going to support the build I'm planning.

**JimM** · #2 Sep 16th, 06, 12:09 PM

Many piston manufacturers stamp the part # into the top of the piston. That number would go a long way in answering your questions.

Craanking compression in psi and cam specs could allow us to back into both your current DCR and your static comp, which would then (along with head casting #) lets us figure roughly how big a dome/ dish the pistons have.

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