Hi everyone, I'm new to the LS1 world after driving a couple 3000GT's and an dumdumdumdumdum. I now am the owner of a 99 SS turbo, and while I do understand some of the basics of completing this goal, I need advice as to how to lower compression on my LS1. It's bone stock right now. I'd assume low compression pistons, but I've also heard new heads. The part that confuses me the most is bore and stroke on the pistons.

 

Well there are three ways I can think of that you can lower compression, one is like you said, low compression pistons, like -8 or even -32cc dome pistons; new heads with say 64 or 68 cc combustion chambers; and a thicker head gasket. Head over to the FI section for turbo set up, and go to internal gen 3 section for bore and stroke measurements.

 

LQ9 heads will lower an LS1's compression to about 9:1

 

Depends on what your looking to do. If you were to toss in new rods and dished pistons you could up the boost or have a little more reliable setup. Otherwise, like stated above you could go with a head with larger runners. LQ9's are pretty cheap to pick up. I vote for new rods and pistons. They will be the more difficult install but you will have piece of mind that your shortblock should hold together for a while.

 

The lq9 /6.0l (71cc) head on a 346 with stock head gaskets will put you around 9.6, 9.7 :1 compression. I have the lq9 (317 castings) with a -4 cc pistion and a .045 cometic head gasket and I'm about 9.2 : 1 compresion.

 

the runners have nothing to do with compression of the engine. Its the combustion chamber size that determines the compression ration with a givin piston.

 

That is what I ment. Combustion chamber. Runners are larger then that anyway, right? like 205, and 225?

 

yeah, i just didn't want him to get confused and buy something looking at runner size and end up with MORE compression.

 

thanks guys. i really appreciate all the help. i just don't want to this thing to blow up. my overall goal is to be able to boost around 15psi.

 

i dont get it, u are a owner of a 99 SS turbo and its bone stock??

 

yeah i didn't get that part either. I think he meant he is the owner of a 99 ss that he is going to turbo. What are your HP goals for the car? There are cars on this forum making close to if not over 500 rwhp with a H/C/I. I see you want 15lbs, so I guess you are shooting for big numbers? You will need to get forged pistons and better rods to go that far I would say.

 

the car is already turbo. has a 60-1 trim on 6.5lbs. has 1 piece aluminum driveshaft, moser 12bolt rear, hotchkis adjustable panhard, hotchkis control arms, star performance spec stage 3 carbon clutch, spec pressure plate, 01 z06 flywheel, pro 5.0 shifter, and an hid 5000k kit.

the block and internals are all stock.

I know that i will need subframe connectors, torque bar, and possibly wider rear tires. of course on top of internals.

as it sits it should be around 450whp and 500+torque. that's just what ls1 motorsports wrote up about the kit.

 

Im assuming STS kit? Your going to have to upgrade that turbo to hit 15 psi, say maybe to a 76MM. Also, for that amount of boost your def going to need some forged internals. Two options: Buy a forged shortblock from a sponsor and sell your stock shortblock for some cash to cover the expenses or you can forge your stock shortblock. If you know of a good machine shop then you can have them hone the cylinders and toss in some forged rods and pistons, otherwise I would just pick up a forged 346/347 from a sponsor and sell your stock shortblock.

 

all the paperwork says it's an ls1 motorsports kit. at this point i have no clue what that means because the website leads to nothing.

 

Sorry is it a front mount kit or a rear mount kit? STS is the major player in the rear mount turbo kits so thats just what I was trying to figure out.

 

oh sorry. it's a front mount.

 

 

Best route to lower compression is to change the pistons.

Using thicker head gaskets or heads with larger combustion chambers works too.

Also, you can lower dynamic compression with a cam that has later intake valve timing. The other methods lower both static and dynamic.

 

Some good reading on how to build turbocharged cars:

Maximum Boost
by Corky Bell

You can usually find it at Borders or just order it from Amazon.

 

Car looks good and good to hear it is a front mount. Again for 15 psi your going to need a larger turbo and id say go with a 76mm turbo (can get it from Dr. Turbo at forcedinductions). Also, you will need forged pistons and rods at a minimum to take the stress of that much boost. Id also say look into geting some 317 ported heads as they are relatively cheap, flow well, and will lower your compression.