Will my compression ratio be o.k. with 94 octane pump gas?

Discussion of the 426 Street / Strip HEMIs.

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illfish
Posts: 2
Joined: Sat Nov 03, 2007 2:27 pm

Will my compression ratio be o.k. with 94 octane pump gas?

Postby illfish » Sun Nov 04, 2007 12:48 pm

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.

George
Posts: 636
Joined: Wed Aug 25, 2004 4:12 pm
Location: Fl

Postby George » Sun Nov 04, 2007 5:52 pm

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.

392heminut
Posts: 488
Joined: Sat Nov 30, 2002 2:16 pm

Postby 392heminut » Mon Nov 05, 2007 9:22 am

I agree with George on both points and think you'll be fine on pump gas. Fire that hummer up and go have fun!
Owner of the Poor Man's Hemi Cuda

mart
Posts: 536
Joined: Tue Mar 22, 2005 2:06 pm

Postby mart » Mon Jan 07, 2008 1:51 pm

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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