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-   -   compression ratio for 91 octane (http://www.clubcobra.com/forums/small-block-talk/37713-compression-ratio-91-octane.html)

Robb 01-11-2003 12:58 PM

compression ratio for 91 octane
 
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 01-11-2003 01:03 PM

George at Gessford told me:

aluminum heads-10.5 to 1,

iron heads 9.5 to 1.

Cheers,
Bill Cook
:D

HighPlainsDrifter 01-11-2003 03:12 PM

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.:cool:

Jeff Frigo 01-11-2003 05:05 PM

Ditto to wicked fast.

flipper35 05-02-2003 01:58 PM

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 05-02-2003 04:24 PM

Robb,

This may help answer your question.

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

Bud


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