I'm putting a parts list together for a new 383 package for the camaro i picked up, I need some input on what you guys have your compression ratio's at and how it runs with today's 91 octane. I was planning on going 10.9 which is what I calculated with the pistons I was going to get. If this was a standard SBC I would have no problem setting it up, but the LTx's seem to deal real well with higher compression and I need the input.

Parts List to date:
vette 4-bolt block .030"
Callies 4340 crank 3.75" stroke/6.00" rod
Manley parabolic I-beam rods 6.0"
wiseco pro-tru pistons or Mahle powerpack pistons
C&A ZGS rings
LT4 cam - or maybe the comp 269HR grind.
LT4 heads - fully ported

 

Man, you could write two or three books on this one because of all the factors involved.

I'll try to keep it real short... but this is how you might go about it in general.

I look at CID of engine and determine hp level to shoot for. From there I need an idea of how much rpm I need to turn to get there. That in itself opens up a whole can of bait....
Cylinder head stuff: cylinder head type and avg. runner volume along with the minimum csa.
Valvetrain stuff: most importantly, whether it will be extremely light (low mass) or more garden variety.
Transmission, converter, car weight, altitude...... long list.

Once you've arrived at a camshaft that'll get you there, you work the static compression ratio such that it achieves you target dynamic compression ratio.

See, we aren't concerned with the static... it's just a means to an end. We want to reach a target DCR... that's the goal.

I saw a 455 ci Pontiac running a static comp of 12.0+ in a magazine write up here a few years ago. It was built by Norm Brandes out at Westech and was part of their "Clean Team" project. The engine had a big cam in it, two cats on the exhaust, some other tricks and it passed the IM240 smog tests for newer V8 powered cars with flying colors.

Neither here nor there, but the important part was the camshaft and how they were running that much static with old RA iron heads? DCR.

If you do a search on the forum for dynamic compression ratio you'll learn a lot. Then you can apply that to your new build.

With an LT1 I'd shoot for ~8.5-8.8:1. Just make sure you don't ignore the importance of a tight quench, a good cooling system and lots of smoothing combustion surfaces to thwart detonation.

-Mindgame

 

That's a helluva a "short answer" MG!! Which I guess it's as short as it can be and still get the point across!

Are those the parts you have already(some of them), or the parts you would like to have?

And definitely dont set a certain CR in stone...in your head! Saying, "I would like to run 10.9:1", is just something that sounds good. Like MG said, it's ALL about the DCR.

 

Thanks for all of the good info, I don't run across many people who use DCR, which is like you said, the correct way to do it. Basically what I am getting out of this is 8.5-8.8. My calculations were putting me at 8.65DCR so I think I am good to go. I am most likely going to try out the comp grind because it appears to have a faster ramp profile, and I would like to try something that we dont already have dyno sheets for.