9.5:1 vs 9.8:1 vs 10.5:1 on 2.0L motor

[kav]

I have decided to go with a new set of pistons for the Canary's engine rebuild and I'm wondering which combination will be best for my motor. I have a 69T 2.0L with stock everything. Looking at Wayne's book I could go with my stock heads, e cam profile, boring the cylinders out to 81mm and a set of S pistons giving me 9.8:1 compression.

Is this the best combination for the motor?

I have the opportunity to buy a set of JE pistons 9.5:1 at a cheaper price, what would the loss in power be over the S spec?

I could get a custom set of 10.5:1 pistons, do I want that?!

Cheers.

-Kav

[Walt Fricke]

With a high dome single plug motor, you'd need race gas to make 10.5:1 work, I suspect. It worked fine on my twin plug 2.7 and 2.8 race motors with big cams and a lot of overlap and two plugs per hole. The guys with Euro SCs (9.8:1) are reporting trouble racing due to the relatively low quality of pump premium.

Google around to see what various opinions are in terms of power lost (or gained) with changes in CR.

[txhokie4life]

Or buy my J&S Vampire Knock Detector / Cionttoller

Mike

[stownsen914]

The dome in the 2.0 heads and pistons is sharper than on the later 911 motors. High compression is their enemy. I believe I've heard that even stock S compression is pushing it with today's street gas. Unless you want to twin plug it or put race gas in for any spirited driving, you'd be safer with 9.5/1.

Scott

[unclebilly]

You may be able to shim 9.5:1 to give you 9.8:1 which is what I did on my 2.7 build.

You can do twin plug inexpensively if you go with coil packs and a crank trigger. The DUI Autotune stuff works really well.

[Henry Schmidt]

Two quick comments:
The theoretical compression ratios publish by Porsche in the early engines is grossly over stated.
Second, be careful with mild cams like 911E with genuinely higher compression pistons.
In the mid range the dynamic compression becomes unmanageable.

[Mark Henry]

Does the present T engine work well? and is it numbers matching? Is this important?

If yes I'd leave it alone and build a bigger "play" engine like a 2.7 or better yet a SC or 3.2 engine.
No matter what size you choose they all cost about the same to rebuild.