With aluminum heads, what's a good compression ratio to run on a blown big block Chevy? All my experience so far has been with LT1 motors, and the reverse cooling probably invalidates a lot of my assumptions.

With a GM502 shortblock and a pair of TrickFlow or AFR heads, I can hit around 8.6:1 off the shelf. I am uncertain whether or not I'll be able to run a decent intercooler yet.

Is that low enough? I'd like to hit around 14psi.

Thanks,
Dave

 

What fuel will you be running? Carb'd or EFI? 8.6:1 is a good number for 14 psi on pump gas.

 

I'll be running EFI, likely a FAST ecm, on pump gas.

 

Im running 8.7:1 on my 496 w/brodix heads and 12 lbs of boost, 93 octane pump gas, 30 degrees total timing and 11.2:1 air fuel ratio (blow-thru carbureted)

I dont have a hint of detonation and is an animal on the street, havent got a chance to tune it at the track yet.

so 8.6 is a very good number!

as Im sure your aware, remember to follow the ring manufacturers recomendations for gap on a supercharged engine

 

Depends on what type of blower you're going to run. Roots likes 8.5: 1 or so and a centrifugal is happy with 9:1.

Jody

 

In very general terms, a BB is going to be a little less tolerant of CR than a small block. But the difference is small. 14psi is a lot on pump gas unless you are running an IC and/or water/methanol injection. Even then, the CR may be too high for that much boost.

Rich

 

Keep in mind that the carbureted motors are also able to use a little more non-intercooled boost because the fuel vaporization leaving the carb venturies also acts as an intercooler to some extent (similar to how alcohol injection cools the mixture). This allows carbed motors to run more boost (approx 2#) than fuel injected motors for a given octane. Just remember your mixture distribution requires more attention on a carbed motor as the intake manifold is the controlling factor to get the proper fuel into the each cylinder.