Ok I'm slowly piecing together a forged 6l for more boost. My question is what kind of compression ratio should I be shooting for? Please give reasons for you response. BTW I'll be running the same turbo that I'm running now probably just a lot more boost.

 

HOW mutch boost are you planning?

 

no less than 9.5:1 IMHO....any less than that and your truck will feel lazy when it is not in boost.

 

As much as this turbo will put out efficiently. Just guessing I think somewhere in the 10-12psi range.

 

It all depends on how much boost you want to run. I agree with blownchevy depending on boost level. When you get higher, low compression will be more important.

 

Depends on what kind of fuel you want to use, how much boost and what size cam. A long duration cam lowers the actual cr. For pump gas with a cooler (10lbs and more supercharged - I don't know turbos) a lot of guys choose 8:1 to prevent detonation. With race gas, meth injection or even pure alcohol and/or spark retard, you can run a higher ratio to get more power. For comparison top fuel dragsters run 45lb boost with 6:1 cr. I'm in the same situation as you. With my new setup (bigger s/c, heads,cam, etc), I'm trying 7.5:1 because I don't want to use any fuel other than pump gas (with N2O). If I don't like it I can always mill the heads.

 

Just saw post you added. For 10-12psi I wouldn't go under 8.5:1. I thought you were thinking like 20+psi. You could go higher cr with meth.

Blownchevy, compared to boost 11:1cr feels sluggish.

 

Your setup in your signature looks alot like what I'm doing. I haven't picked my cam yet, I'm leaving that to cammotion. What is your cr going to be and what is your part# for those pistons?
The only set that I have found that will get me even below 10:1 is this set

126-11517 Diamond Pistons LS1 Forged Dished Piston set w/ -15.0cc Dish, 4.030" BORE / 3.622" Stroke / 6.125" Rods / 1.310" Comp Height / .927 x 2.950 Wrist Pins Included

With this set the cr will be 8.75:1

 

[QUOTE=AintNoHo]Just saw post you added. For 10-12psi I wouldn't go under 8.5:1. I thought you were thinking like 20+psi. You could go higher cr with meth.


I will go 20psi if the turbo can do it, I doubt it will. Basically I will push this turbo to the max and if it's not enough I will just upgrade.

 

My advice: pick your boost level (even if it means you have to upgrade your turbo down the road) and build your engine for that level.

I ran 10.1:1 with 10-12psi with meth only as the intercooler on stock LQ9 low end parts. I'm not familiar with the precision turbos, but my Garrett GT67 still had plenty at 12psi -- I'm pretty sure you can pull off 15psi no problem.

I built this block for 18psi and targeted 8.6:1 CR with my cam (and meth+intercooler of course).

The rule of thumb on CR should be to run as much as you can and still get your boost in.