Compression vs Detonation vs Gas
Thread Starter
Melting Slicks
Joined: Jun 2009
Posts: 2,343
Likes: 4
From: Anderson SC
Compression vs Detonation vs Gas
The partial engine (427 SBC) I'm looking at for Phase II - claims 10.1 and will run on pump gas. I was already a little skeptical and the above post seems to confirm this. What's the safe compression for regular gas?
-W
Melting Slicks
Joined: Mar 2006
Posts: 3,456
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From: Piedmont Va
St. Jude Donor '11-'12-'13,'19-'20
Assume when you say "regular" gas your talking 87 octane!? If yes then I think 9.5:1 may be a problem. I have 10:1 and run fine on 93 Gasahol with gobs of advance in my 383....but wouldn't try anything less.
My guess would be 9:1 or less.....I'm sure more expert opinions will follow.
What's the safe compression for regular gas?
Last edited by CheezMoe; Jul 26, 2009 at 04:17 PM.
Thread Starter
Melting Slicks
Joined: Jun 2009
Posts: 2,343
Likes: 4
From: Anderson SC
I'm not running *any* cam yet... I'm looking at the World Products 427 SBC and I'm kinda skeptical of thier claims at 10.1 / 1
Note that I'm a long way from Phase II, I just want to learn early to get a plan on paper.
-W
Last edited by Clams Canino; Jul 26, 2009 at 04:49 PM.
Le Mans Master
Joined: Nov 2008
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From: columbus oh
Le Mans Master
Joined: Apr 2006
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alumnum head disipating heat much faster then iron, modern updated shaped combustion chambers won't need as much advance it will handle it no problem.
Last edited by Little Mouse; Jul 26, 2009 at 04:58 PM.
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
Cam plays a major role in it. Ihave seen 11:1 motors on pumps gas with no problems. I have also seen iron headed 9.5:1 motors rattle like crazy. I run a 10.7:1 AFR aluminum heads with a big solidcam with no problem on pump gas. There is no set compression that is safe. To many variables.
Burning Brakes
Joined: Dec 2003
Posts: 1,004
Likes: 7
From: Adelaide South Australia
with above comments about alloy heads and cam.You can generally run about 0.5 ratio more with aluminium heads over cast heads for starters....
Also, as cam duration increases, you can run higher compression ratios.
The compression ratio stated on engine buildups is the static compression. The issue with detonantion is related to the dynamic compression ratio.... that is, the actual compression achieved when the motor is rotating, and the bleed off during the overlap phase is taken into account.
Also, higher octane fuel allows for more compression too.
so choose your engine buildup depending on what your primary design goals are.
cheers
tom
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edit-Sorry for the momentary hyjack.
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My original roller cammed 427 SBC was something like 10.4 with 64 cc heads. I always ran the local 91 octane. My present 434 is 11.7 and it run fine on 91 with a larger roller cam.
