Detonation on a BBC

[Keith Tedford]

We have an L78 4 speed Chevelle with 4:10 gears. It is living on 92-93 octane gas. You don't want a quick advance curve in the distributor and you have to back off on the timing a little. Cast iron rectangular port open chamber heads will drop the compression about a point. A longer duration cam will bleed off some cylinder pressure as well. A true 11-1 compression L72 is going to have real problems on 92 octane gas.

[COPO PETE]

Rob is 100% correct on this one. The average L-72 is hard pressed to make a true 10:1 Compression. Put a thicker head gasket on and back the timing off a bit. With some super in the tank and maybe a little octane boost, you'll be fine!
Peter

[IRONCLAD]

HOLY COW!! I DIDN'T EXPECT SUCH A GREAT RESPONSE BUT I AM GRATEFUL FOR EVERYONE'S SUGGESTIONS. I DIDN'T LIKE THE IDEA OF WATER INJECTIONS BUT I THOUGHT I WOULD THROW IT OUT TO MASSES, HERE. I AM NOW ELIMINATING THAT FROM MY LIST OF SOLUTIONS.

MY GOAL WAS NOT TO GET THE HIGHEST CR POSSIBLE BUT TO BEAR WITH THE STOCK CR OF THE ENGINE ON THE GAS WE NOW HAVE AVAILABLE. IF THE STOCK COMPRESSION IS MORE LIKE 9 1/2-10 TO 1, THAT IS FINE. I JUST DIDN'T WANT TO RUIN MY ENGINE WITH THE DETONATION.

I THOUGHT OF ALUMINUM HEADS AS MOTION SOLD THEM ON PHASE III CARS AS AN OPTION BUT I WAS UNDER THE IMPRESSION THEY ARE VERY EXPENSIVE; I HAD ESTIMATES FROM BOTH TRACY PERFORMANCE AND CRANE CORVETTE AND THEY OFFER BARE CAST IRON L-72 HEADS FOR ABOUT $1500; I WOULD HAVE TO REBUILD THEM WITH MY OWN PARTS. I HATE TO SEE WHAT THEY WOULD WANT FOR ALUMINUM ONES; MAYBE I'LL KEEP AN EYE OUT ON EBAY.

THANKS AGAIN, EVERYONE. IT IS SURE NICE TO HAVE A LOT OF FRIENDS OUT THERE THAT WILL SHARE THEIR KNOWLEDGE.

GARY

[69L89396]

I think you can get away with more compression with the aluminum heads and still have the timming.
My 2 cents

1 other thing is to look at the dynamic compression ratio

[Edited by 69L89396 (02-18-2002 at 10:39 PM).]