Howdy folks. Odds are I just didn't word my search correctly, so I couldn't find my answer. So, I suppose I should start from the top....

I purchased a 1994 LT1, shortly thereafter the motor went (long story, for another time). Now, being the moderate guy I am, I figured since it was blown up, I might as well go 383. The block has gone .030, the heads have been P&P'ed, and match-ported to the manifold. The rotating assembly, no matter where I get it from will take a trip to the machine shop for balancing. I have an aftermarket single-mass flywheel, and centerforce clutch. Hot Cam, 1.6 RRs, GMPP roller timing set, new Opti, and a few other doo-dads.

So, now we come to my actual question. I'm getting conflicting stories from my builder, and my parts guy. The parts distributor sas that with the stock heads I shouldn't go above 10:1 Static CR. My builder thinks anywhere up to 11:1 should be fine. Now, the LT1 was 10.4:1 to start with wasn't it?? Who's right? I've been looking at a fully balanced assembly from Go Fast Stuff dot com. It's pretty inexpensive, and includes a choice of KB slugs. The KB 197s are what I've been looking at. With a 58cc head they give a 11:1 ratio. The dynamic CR, according to their calculator with the 12cc dish comes out to about 10.3:1 DCR. The KB 134s which are flat tops with 7cc valve reliefs end up at just about 11:1 static CR.

This was an unplanned build-up, you have to understand. As such I'm on a budget. The plan is to build the bottom end fairly well, and play catch-up with the top end next spring when I can have saved up more money.

The car is a street driven car. If it makes 5 to 10 passes down a strip it'll be alot. I do some autocross stuff though. I'm really loking for mostly bottom-end grunt, without running out of air up top.

So, to sum up, I'm seeking the advice of much more experienced than myself, C4 gurus. Thanks in advance folks.

-DarkMatter (Lou)

 

Listen to your builder.

 

You will find a lot better information on LT1 building at this forum: http://web.camaross.com/forums/forumdisplay.php?f=9

I'm no expert, but I've been reading the opinions of the experts for a few years now. Based on what I've read:

- 10.3 DCR is too high. Target is in the 8.5-9.0 range.

- 11.0 is trivial for static CR. Plenty of people running 12+ on LT1s. The person who said 10.0 doesn't know what he's talking about.


- You will run out of air on top with a 383 if you stick with stock heads, unless you're spending like $4k on porting.


But don't take my word for it. Go over there and do some research.

 

Thanks for the link Vis. I know the stock heads won't do the job of really keeping the motor breathing with the extra cubes. Like I said, it's a band-aid until I can squirrel away some more cash for heads.

Checking you link now though. Thanks again.

-DM

 

Your builder doesn't know much about LT1 specifics. Yes, stock is 10.4 and on my first rebuild I used -6cc pistons and had an 11.3 CR with .029" gaskets. I ran this engine for many miles with no issues. On my newest one I'm using -16cc pistons (because it's zero decked) and static compression came in at just a tad under 11:1. Due to the inherent efficient combustion capabilities and superior head cooling of these engines, 11.5:1 or more is not uncommon in a street engine if designed properly.

 

Thanks for checkin' in.

Actually, my builder is the one that said 11:1 shouldn't be a problem at all. It's the old-school "gent" at the parts supplier that thinks that anything over 10:1 is suicide. I just couldn't possibly understand that. Then I started thinking maybe the increased swept area had something to do with it. So, I decided to turn to the forum for answers.

-DarkMatter

 

Sorry, I misread then. As long as you got the right info, though. My parts supplier thought I was crazy when I ordered a 3.80" stroke crank with pistons that have a compression height for a 3.75" stroke. Someone recently sent me a link from their site where they are now offering as a package, the exact crank, rods and pistons I ordered last year!