Compression Test vs Compression Ratio
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From: Indy Indiana
Compression Test vs Compression Ratio
I ran a compression test on my 454 (Late 73 block), it has 150 pounds pressure in each cylinder. If I remember right, then equal pressure is more important than total pressure readings that might be skewed by piston dome and cam timing.. or open chamber vs closed chamber.. I also have late '73 open chamber square port heads.
Is there any relationship for compression ratio to compression pressure in a compression test that I could use to determine compression ratio and therefor conclude what octane gas I should be using?
I have no idea what cam I have and what kind of pistons I have.
Thanks Folks!
Is there any relationship for compression ratio to compression pressure in a compression test that I could use to determine compression ratio and therefor conclude what octane gas I should be using?
I have no idea what cam I have and what kind of pistons I have.
Thanks Folks!
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I'm sure 150 psi can run on 87 octane in your case.
To answer your question...it's a little tough. A big cam will often show low cranking compression even with high static compression ratio. It will run around fine on low octane gas at low throttle opening. It's when you open it up and all that air rushes in and actually FILLS the cylinders you will get detonation. Usually up to 190-210 cranking compression can get by on 93 octane if tuned right. Sometimes a little more...but it's edgy.
Your stock 454 was lucky to have almost 8.0 honest compression ratio. If it's been upgraded to a domed piston and or cam changed..it's pretty much trial and error. But I wouldn't expect it to be too bad unless you have a pretty serious cam in it.
JIM
To answer your question...it's a little tough. A big cam will often show low cranking compression even with high static compression ratio. It will run around fine on low octane gas at low throttle opening. It's when you open it up and all that air rushes in and actually FILLS the cylinders you will get detonation. Usually up to 190-210 cranking compression can get by on 93 octane if tuned right. Sometimes a little more...but it's edgy.
Your stock 454 was lucky to have almost 8.0 honest compression ratio. If it's been upgraded to a domed piston and or cam changed..it's pretty much trial and error. But I wouldn't expect it to be too bad unless you have a pretty serious cam in it.
JIM
