I know you can run more boost with lower compression, but what would be a decent ratio for a turbo, probably around 8 or 9 psi. Also, are there ways to lower compression besides smaller cc heads?

 

Cometic gaskets makes head gaskets in several thicknesses. You can probably add a cometic gasket that's slightly thicker to lowr compression. Not sure how much but give them a call as I'm sure they can tell you. There is good and bad to this. Headgaskets ae made to be the protector of the engine... Die a brave death, to save the internals of the engine in case you go lean, ect. If you do have a problem with your tuning and you have the cometics on(steel shimmed gasket) the gasket won't be the first to go and you will have an engine build up on your hands. If you do have a good tune you could push the limits more. A Feelpro Gasket is good for a theoretical compression ratio of ~12. Some get away with more but that's a safe cr. The cometics say they are good to a theoretical compression ratio of ~18 although I've seen them run with upwards of 24lbs of boost with no problems.

To find your theoretical compression ratio take your boost and devide it by one atmosphere(14.7), then add one, then multiply it by your compression ratio.

Example: ((Boost/Atmosphere)+1)*CR
If your compression ratio is 9.5 to one atmosphere and your boost is 8psi then ((8/14.7)+1)*9.5=Theoretical Compression Ratio, which is 14.67

If you can reduce your compression ratio to 9.0 to one atmosphere and your boost is 8psi then ((8/14.7)+1)*9=Theoretical Compression Ratio, which is 13.9

Similarly 8.5cr=13.13, which at 10lbs of boost now only puts you at a theoretical cr of 14.3.

This should kinda explain why lower compression ratio's can run higher boost levels.

 

You lower compression by using larger cc heads

 

sorry I missed that [:@]

 

damn, mustve mixed that up somewhere. Well thanks for all the advice. I think i understand everything i need to...now only problem is another grand for a turbo. Any opinions on turbo kits or companies. I was mostly looking into the HP performance kit, because it comes with everything i need to get it running, but ive heard good things about CarTech as well.

 

How much boost you looking for? Give us an idea of what your gonna be running and we'll give you an idea of what compression ratio you should shoot for

 

Not sure yet really...dont really want to replace the internals yet, so how much would be safe to run on stock internals?

 

stock pistons are hyperutectic not forged, and compression ratio is in the mid 9's and stock rods are cast powdered metal - meaning about all you can safely go is about 12 psi, and thats at the top of safe... Ive heard people running 14 but they had the $$ for a new engine when the time comes

 

Alright well i wasn't planning on going over 10 anyway. Will the stock compression be alright?

 

YEah... 10 psi on stock compression is fine.