racin66coupe

whats the highest compression ratio you can run on pump gas?

JMD

The question has more than one answer!

But my general rule of thumb that has worked for me is 9 to 1 for iron heads 10 to 1 for aluminum.

If you are running a big cam, add up to one full point.

I am at about 4,000 feet elevation, so my rule might be a little high the closer the elevation is to sea level.

Just FYI, we are running 10 to 1 in my sons p/u, and 11 to 1 in the Mustang, the Mustang has a pretty big cam though.

The 10 to 1 in the truck was close to being too much with a mild cam, but since we have changed the cam it is much better.

Oh, they both have aluminum heads.

67mustang302

Yeah, there's about a dozen other things that affect detonation resistance, so compression rules of thumb are just rules of thumb. Head material, chamber shape, cam profile, quench height, piston dwell, all those will determine what kind of fuel the car will be able to run. Not to mention the tune.

67coupe

I have 58cc iron heads with flat tops and it comes out to 10.4:1 with my deck clearance. I use a 525/290 cam in the 302 and it runs great on 97. I can even get by with regular, but performance suffers some at low rpm.

racin66coupe

would i be able to run pump on a 10.7:1 engine? thats the comression ratio that the scat stroker kit i am looking at has with 64cc heads. speaking of it, how big of a chamber do gt 40 heads have?