Compression Ratio Octane Requirements
Thread Starter
Burning Brakes
Joined: Oct 2006
Posts: 1,089
Likes: 43
From: Native Californian CALIFORNIA
Army
Compression Ratio Octane Requirements
Here in California the highest pump gas would be 91 octane unleaded
In building an engine what is the breaking point for a compression ratio to still utilize pump gas?
In building an engine what is the breaking point for a compression ratio to still utilize pump gas?
Race Director
Joined: Sep 1999
Posts: 11,360
Likes: 382
From: Plano TX
It's not that easy. The octane requirement depends on the dynamic compression, not static. The later the intake valve closes, the less cylinder pressure you build and the less octane you need. If that's not enough, the quench is also important.
Some rules of thumb:
With iron heads and a moderate cam you need to stay well below 9.5:1. Probably closer to 9:1.
With aluminum heads you can bump that some to 9.5-9.8:1.
I just finished my 454. Aluminum heads, moderate cam (224/230 duration), 0.044" quench. It's 10.15:1 and does not ping on 93 octane.
Some rules of thumb:
With iron heads and a moderate cam you need to stay well below 9.5:1. Probably closer to 9:1.
With aluminum heads you can bump that some to 9.5-9.8:1.
I just finished my 454. Aluminum heads, moderate cam (224/230 duration), 0.044" quench. It's 10.15:1 and does not ping on 93 octane.
Melting Slicks
Joined: Feb 2006
Posts: 2,209
Likes: 0
From: Mo
Believe it or not,I ran a 12.1 396 lt1 on premuim p/g,the 710 I had in my pro street car 11.5.1 and ran the same.both engine's required alittle detuned set-up for it but ran well.
Like said early there's to many variables,to say just what comp ratio runs in a octane ratio.
PHR did a awesome story on building a high compression p/g engine acouple months ago.
Like said early there's to many variables,to say just what comp ratio runs in a octane ratio.
PHR did a awesome story on building a high compression p/g engine acouple months ago.
