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Will my compression ratio be o.k. with 94 octane pump gas?
Posted: Sun Nov 04, 2007 12:48 pm
by illfish
I'm a bit concerned about my compression ratio and pump gas. The motor is an all aluminum 572 Hemi with about 10.75:1-11:1 compression. My calculator puts it closer to 11. This is static CR. The cam is a 619 lift/255 @ .050 with a 110 LSA. I'm planning to run a total of 30 degrees timing to keep it out of knock but would run more if able. Assuming I keep the water at 160 and the oil at 200, can I get by safely on 94 octane? I've run up to 12:1 on the street in the past, just not a hemi.
Thanks in advance.
Posted: Sun Nov 04, 2007 5:52 pm
by George
Accepted knowledge is you can run 1 point higher comp with a Hemi on the same octane as a wedge engine. The greater heat conductivity of aluminum robs the engine of 1 point of compression through heat (energy) loss vs an iron head. This would lower octane requirements also.
Posted: Mon Nov 05, 2007 9:22 am
by 392heminut
I agree with George on both points and think you'll be fine on pump gas. Fire that hummer up and go have fun!
Posted: Mon Jan 07, 2008 1:51 pm
by mart
George wrote:Accepted knowledge is you can
run 1 point higher comp with a Hemi on the same
octane as a wedge engine. The greater heat
conductivity of aluminum robs the engine of 1
point of compression through heat (energy) loss
vs an iron head. This would lower octane r
equirements also.
-------------------------------
Also, running that much cam will bleed of a lot of
cylinder pressure until the thing's wound up pretty
high. At low and mid-range engine speeds- which is
where the engine wil be most of time, if it's on the
street at least - the cam will give the *effect* of
running a point or two lower compression ration
mart
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