are those of you with 8.5:1 CR happy?? or do you wish you had of gone with a 9.1:1 CR of even a tad higher. Sorry for all my posts with questions but my built will begin very shortly and as you all know this isn't cheap, I just want to have no regrets latter. Thanks for any info. You guys have really helped so far!!

 

Im wondering the very same question to. so guys?

 

either way you should be fine, any turbo car from the factory has 8.5:1 CR so you cant go wrong their, you can run more boost. with 9:1 CR you will make same power with less boost but be more prone to detonation, I guess 8.5:1 would be the safe way to go even though I have some 9:1 sitting at home

 

We recommend and build a great majority of our motors with 9:1 CR..this offers crisp response when under vacuum, and is still low enough to run lots of boost without any worries...

I like 9:1 because, when tuned properly, one can run a greddy or aps tt at the turbo's peak effeciency and make over 600rwhp (or close to it)

with 8.5:1, you need to run more boost to make the same power, and you start to run out of turbo

-TODD

 

9:1 Max and ya --Better response. The 8+:1 to 9+:1 is great and a little playin field between that point on C/R---Its kinda a fine tune desision

 

great tips I think I will go with the 9.1 CR, thanks for the info

 

9:1 is Snappy but just think bout what u want to do before u do it

 

My installer and I Just had this conversation And told me it was better to have 8-5-1 rather then 9-1 but i have run 9-1 before and all was well. the lower you go like stated above the more boost you have to make up for it. But also rem. alot of turbo motors from the factory run around 8-5-1 just something to think about?

 

8.5:1 will allow more boost and more timing than running a higher compression ratio.....out of boost you can run more aggressive timing for better off-boost response, and on-boost timing can be higher for more power as well as more boost.

if 1-2psi difference run between 9:1 and 8.5:1 means you're running out of turbo, you're already on the ragged edge anyways!

 

+1

 

It's probably splitting hairs. I have run the 8.5:1 and the 9.0:1 in my engines, and could never tell the difference behind the wheel or on the dyno. With a good tune, you shouldnt have no trouble with either. Keep in mind, at right around 600-650whpwhp (true whp...no fluff), people are going to need to switch to higher octane fuel, as there is a hard limit it terms of what we can do with pump gas. And once you switch to race gas, there will be no meaningful difference between 8.5:1 and 9.0:1.

 

good thing there's a pump with 100 octane in my city I can go to any time

 

is one compression cheaper than the other? and i'm taking that 8:5:1 is safer than 9:0:1?

 

Selecting the compression of the piston should fit your desired power goals. Id go with 9.5:1 for 450-500 rwhp goals. This is assuming stock sleeves as well. You can run less boost and the open deck will keep things cooler. You get great response off boost. If you pair this with the APS TT, spooling will be almost instant. Id go with 8.5:1 if your goals are for big horsepower, like 550 rwhp+. The lower compression provides a basis for a higher level of safety. At 650 rwhp, you will just about have to run some race fuel. There is only so much you can do with 3.5 liters.

 

Last year I was 8.5:1, This year I am 9.0:1.

No noticeable difference.

 

I would agree with Sharif . Ive had both 9 to 1 and 8.5 to 1 in the G35 motor and cant really tell the differnce .

 

and for those of us that like to live on the ragged edge, this is an issue