perplexing situation

[Keith Tedford]

We've put over 30K miles on our L78 Chevelle since we bought it in 1997. No ill effects so far on 91-93. Being stock factory, the compression ratio might be closer to 10-1. Seems that many have been found to be down a point and more.

[indyjps]

calculate your true comp ratio before its assembled

[BBIGG BLOCK 396]

I hate butting in on you guys but here locally a lot of guys are beginning to have a lot of problems with the HIGH PERFORMANCE FUEL! Seems they are reformulating them and adding ETHNOL or some other OXYGEN BASED ADDITIVES which is causing major problems when left sitting for a couple of weeks.A lot of guys have had to have ther carbs redone because of this problem.I would surly be checking on the racing fuels you are using for additives to your Hot Rods to make sure it is not one of the reformulated brands.I will try to find out the names of some of the fuels they are having problems with and post them.

Bobby

[Chevy454]

The first L72 I put together came in at 10.2:1, after a slight clean up on the deck, with the stock TRW pistons, and the .038" Fel-Pro...unless it was the dead of summer, I ran it on pump gas...took our Y-Camaro to 12.7s @ 108+ (woulda been better had I known then what I know now!).

[jasonL78]

Tommy great topic! I am asumming this is the motor for your 68 BB nova? I was pondering the same thing with the new motor I am building for my 68 L78 nova. I have a stock l78 short block assembly with the 11:1's and my machine shop told me to change them as well. This topic just changed my mind to keep the high compression slugs. Do any of you use the high test from the pump (93) and then use an over the counter additive, like octane boost 104. Or should you just use race fuel like cam 2?

Jason

[Andy]

What are the cam specs that are going into these L78s? Have the blocks been decked? What CC are the heads, and how many CCs do the pistons displance(valve reliefs[flat top], domes[dome top pistons], dishes[dished pistons])? I bet that you could get an aftermarket grind from comp, crane, crower, lunati, or isky that would make more power, and would allow you to run pump gas. With the problems mentioned with some of the reformulated race fuels, it probably wouldn't be a bad idea to build a motor that would not have to have race gas. Most of our cars sit up at one time or another and who wants to deal with the hassle of rebuilding carbs or draining fuel tanks.

[Chevy454]

Fellas, I'm telling you, with the stock pistons, on a 34cc dome, you'd be *lucky* to see 28cc across the board (more likely gonna be 26-27cc each)...don't get wild on decking the block (a little is ok)...run the good Fel Pro .038" head gasket...and I bet you'll be right at 10:1, especially being we're talking 396s. Even better, go buy a cheap cc'ing kit (well under $100), and check it out for yourself...

I would recommend the Crane/GM blueprint '143' cam, as I believe it's a better cam and I'll just about bet it'll be cheaper...

We raced our stock spec L72 on pump gas all the time, except in the hottest part of the summer we'd add just a splash of race fuel...I'm not a fan of the octane booster stuff.