Detonation on a BBC

[IRONCLAD]

Does anyone out there know anything about an Automotive Performance Inc. MK-II Vapor Injection (water injector)....like what years they were used for and if they are compatible with a 1969 BBC, with closed chamber, rectangular ports? I know this is a long shot but hope someone knows!

I don't want to put oval heads and bring the CR down to a ridiculous ratio of 8-1 with a great engine like the L-72. However, I want to able to drive it around town if I want to.
Some people say to double the head gaskets, some people say to use TRW "Turbo" pistons, stellite valve seats and bronze valve guides and still others say, use water injection.
I cannot get Sunoco High Octane in the South here nor have I got connections to Aviation fuel. And I don't know if an Octane Booster down the local NAPA store will actually help.
Any recommendations? Thanks.

(Gee, It's hard to write all these upper and lower case letters all the time - hope it makes the "Administrator" happy)

[Stefano]

A stock L-72 needs High Octane, for the engine to survive detonation and pre-ignition. Water injection alone will not be sufficient.

I am not aware of any bolt on GM performance heads that will reduce the Compression of a stock L-72 to 8 to 1. You can however fit after market aluminum heads which will both reduce compression via larger open chambers and dissipate heat much better.

The aluminum heads will thus, allow you to run a higher compression. Premium fuel, octane boost and proper cam and ignition timing will allow you to run your BBC on the street.

The heads can be painted to provide a stock appearance.(Cost approx. $2,000.00)

Better yet, buy a GM crate 454 HO with 425 HP @ approx. $4,700.00, it runs on premium pump, you can drive it cross country and park the L-72 on an engine stand.

Just my jaded opinion.

[Chevy454]

You guys would be real surprised at what the actual compression ratio of a STOCK L-72 is! Believe me, it's NOT 11:1! The deck clearance on dad's L-72 was only .013", and the heads were shaved .010", and when the dust settled, it came out at a whopping 10.2:1. Scott Tiemann did a DEAD STOCK L-72 last summer(?) for a Berger car, and it came in at 9.8:1.

Now, if a guy does a lot of decking/shaving, and gets some healthy pistons up in the holes, then you could get wild on the compression ratio. I'm not saying you can run straight 87 out of the pump, but premium gas and mix some octane boost or racing fuel with it, and you will be fine.

[bbdon]

I have used the Edelbrock Varajection setup, and while I cannot really blame Edelbrock for the trouble I had, I ended up taking it off pretty quickly. You need to use only distilled water in the system, and if you don't the small passages will fill up with corrosion quickly. It was a pain in the neck. I ended up rebuilding the engine and installing TRW L2240NF pistons. These pistons have extra material in the dome area so that they can be custom machined. I had them machined to remove most of the dome. This solved the problem permanently. My engine is a 396, I think that the 427 equivalent piston is the 2300NF. For some reason when I search for these numbers now I get Speed Pro numbers as often as I get TRW. Maybe they are the same company now?
Here are some web sites with information.
http://www.federal-mogul.com/speedpro/product_technical_guidelines_speed_pro.html
http://www.flatlanderracing.com/trwchevy396_427.html

[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).]