how to tell what compression i have

just got a new boat. trying to figure out what compression i have in engine. is they any way to tell with out taking heads off and looking a pistons. 1980 454, Iron Chevy Heads with Rec ports. motor looks to be built with all high performance stock chevy parts.

what would the compression be from circa 1980?

Motor sound real good.

To know for sure, you have to know the piston dome or dish volume, head chamber volume, bore, and stroke.

There is an instrument called a whistler, used to inspect motors. But fairly expensive prolly for what you are curious about.


http://katechengines.com/motor-sports/services/whistler/

Otherwise, like BDMar says, got to take it apart.

A close ball park figure will be to divide the compression by 14.7 so let's say your at 150 psi divided by 14.7 is 10.2 to 1 ,otherwise you'll be doing a whole lot of measuring and you have to know what cam shaft you have because that changes compression ratio too.

rush1 said:

A close ball park figure will be to divide the compression by 14.7 so let's say your at 150 psi divided by 14.7 is 10.2 to 1 ,otherwise you'll be doing a whole lot of measuring and you have to know what cam shaft you have because that changes compression ratio too.

Click to expand...

????
How does a camshaft change the static compression ratio?
I understand that the cam can affect the effective compression ratio but only to a smaller degree.
I re read the op and Rush is right. Closest way is the compression test method.

Instigator said:

????
How does a camshaft change the static compression ratio?
I understand that the cam can affect the effective compression ratio but only to a smaller degree.
I re read the op and Rush is right. Closest way is the compression test method.

Click to expand...

Camshaft will change the dynamic compression ratio not static , but your dynamic compression ratio is the actual engine running compression ratio (when the valves are closed in relation to where the piston is at in the bore )