compression ratio for 91 octane

[Robb]

What is the highest compression ratio you can run, when you plan to use 91 octane gas?
(no gas addives?)

First, assume aluminum heads.

Second, assume iron heads.


Thanks,
-Robb

[wicked fast]

George at Gessford told me:

aluminum heads-10.5 to 1,

iron heads 9.5 to 1.

Cheers,
Bill Cook

[HighPlainsDrifter]

Robb;
A couple other things to consider besides static compression is cranking compression.Alot of timing will detonate also.
Total timing should be 36 to 38 degrees.
You can get away with a little more compression if you run a cam with enough duration to bleed off some low end power. eg; say 230 to 244 degees at .050 lift will be more tollerant than a 210 to 220 cam.
Perry.

[Jeff Frigo]

Ditto to wicked fast.

[flipper35]

On the Mopar engines I hace seen 11.2:1 in AL and 10.5:1 with Iron, both with cams using the correct ramp speeds for the larger MP lifter bore.

Also, the timing is dependent on several things including piston shape and cumbustion chamber. For instance a quench style head/piston will require 36* and a flat top regular wedge chamber requires 34* because the flame front spreads quicker here. Of course this is for a Mopar small block and your requirements will differ.

[George Snyder]

Robb,

This may help answer your question.

http://cochise.uia.net/pkelley2/DynamicCR.html

Bud