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?

Post 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.
George
Posts: 694
Joined: Wed Aug 25, 2004 4:12 pm
Location: Fl

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

Post 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!
Owner of the Poor Man's Hemi Cuda
mart
Posts: 536
Joined: Tue Mar 22, 2005 2:06 pm

Post 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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