[d^2]

Howdy

I have a new 454 crate motor with cast iron heads with a 8.75:1 compression ratio. I was wondering how high I could go but still run on 89 octane gas?



Thanks

[DoubleVision]

You can go up to about 9:1 on 89 octane. You can even bump it up to 9.5:1 if you carefully tune it with a modest timing curve. However, bumping up the compression from 8.75:1 to 9.5:1 is such a small gain you won`t notice any difference power wise which makes it not worth doing.

[454C10]

Depends on cam timing, temperature, and load (gears, trans, weight).

For example. I use a 454, 8.75:1, in a 4200 pound truck, 3.08 gear, th400, and a compcam 260H. It will ping if I pull a light trailer with 89 octane in the summer (95F).

If you are running a mild cam (less than 265 degrees advertised) then stay with the 8.75:1.

In general, A 268 degree cam can handle 9:1, 270 degree use 9.25:1, 280 use 9.5:1, 290 use 10:1.

A BBC will not tolerate compression as well as sbc.

[d^2]

I also have a 396 out of a L35 Camaro. It has 10.25:1 in it. Will it ping if I put it in a pickup that I tow heavy loads with?



Thanks

[302 Z28]

Originally Posted by d^2

I also have a 396 out of a L35 Camaro. It has 10.25:1 in it. Will it ping if I put it in a pickup that I tow heavy loads with?
Thanks

Most definitely, unless you run 93 or some octane booster.

Vince