9:1 or 8.5:1

[Shane@DBPerformance]

There is no such thing as an ideal compression ratio. It all depends on what gas you want to run, how close to the edge you want to tune the car, how hard you want the car to be able to tune, how much responsiveness you need. Lower is going to let you run more boost on pump gas, but the car will be a bit more doggy out of boost and you gas mileage will not be as good. There are some guys out there running built motors with pretty low compression. Lancerman runs 7.7:1 compression in his AWD 4G64 Lancer that runs 10s on pump gas. There are some other guys out there too that run low compression so they can run insane boost levels on race gas. Extreme's 8 second AWD Talon was running 7.5:1 compression pistons last I read.

[Raptor]

Depends a lot on what the application is. If you are going to build a car more for street and DD and care less about maximum power, go with the 9:1 so you have better spool up and it is more tollerable off boost. Otherwise, there are arguments to be made for going with less compression as Shane mentioned. You can compensate for the lower compression with more boost and end up with more air in the combustion chamber (more volume), combined with long rods causing more dwell time at TDC to build pressure, which will create a lot of power. There are a number of other factors to consider as well, but there is enough info in this thread to get the decision made.

[santa]

I see what your saying about tuning as far as c/r.

[Goat Blower]

9:1. Don't be a pansy.

[red7mgte]

Well after talking to the owner, and listening to him i realized how much abuse this car has in its future. I see the lower compression being a better way to go as far as reliability issue are concern.Not sayin that the CR will directly affect reliability but the fact of the hand holding the bosst controller, once it is no longer in my possesion.That is how it got in to my hands in the first place.

[santa]

What the heck did you just say at the end? That makes no sense....and niether can the guy next to me...

[Pimpin Dsmstyle]

dude was messing the the boost controller ( turning it up im sure) and obviously went higher than the engine could handle. This guy is not the owner. I believe someone is coming to him for help.

[awd-drifter]

If you got a low c/r of say...8.5:1, is it good for the 4g63T motor to go straight to NOS, because there is more air to suck in? well, I thought about it, but wouldn't NOS work to much on the stock turbo? Man, I have alot to learn about these kinda things before I get my DSM, just asking through curiousity though. Thanks!

[Shane@DBPerformance]

More air to suck in? What do you mean?

[Super Bleeder!!]

he probably thinks that if the piston has a lower compression then there must be more volume in the cylinder and hence more room for air. i don't even know how to being to explain this one...gahh