What's the best way to increase compression?

[TechnoViking]

I'm contemplating making a Euro out of my US 911 SC engine (which is currently in about a million pieces ).

I have identified 3 ways to increase compression:

1. Buy Euro P&Cs.
2. Machine head mating surface so that it sits lower on the piston
3. Offset boring piston ring busings

#1 is straightforward, but pricey. What about #2 and #3 or other methods? Any pros and cons I should be aware of?

[911st]

I am not an expert but I will take a stab at it.

If you need to reservace your head for some reasion, just do that.

Machining the head or case may require machining the chain housing so ever thing is ok.

Thus, stretching the rods may be a best of the three.

However, make sure you have someone that knows what they are doing. On a turbo, you have lots of clearance for moving the pistion closer to the head. Not sure on the SC's and or if your valve clearance for that matter.

You could look for a used set or concider J&E's.

[Buckterrier]

I had my 3.2 rebuilt this past spring. The mechanic machined .002 from the top & bottom. He did the top to add a turbo gasket. This apperantly gives ROW compression. One problem that can happen is the coatings inside the jug can chip and cause problems.
In hindsight I wouldn't have had it done. Not because it doesn't run good, it does. But now I can't add a turbo at a later date

[otto in norway]

Hello!
I think you may only need to buy pistons. (JE) They make all sorts of compression pistons. However you need the Nickasil cylinders to do this, or you can have the Alusil cylinders prepared with Nickasil.

I bought a set of JE's (comp 9,5:1), but found out later that I had Alusil cylinders. So I sold the pistons, and bought a new set of P/C's from Mahle (Nickasil), with comp. at 9,8:1. (NOT cheap)

[Grady Clay]

Martin,

I would follow Otto’s lead and buy new Mahle Nikasil P&Cs. I agree that they are NOT cheap but they will give you what you want and last the life of your car. Not so with JE as they seem to be 20K limit.

I would use the 98 mm variety and keep the CR just under 10:1, 9.5:1 would be better with CIS cams. You have the opportunity to convert to twin ignition. Call Steve Werner and chat about this.

Are you coming to breakfast Saturday? I’m going to Pueblo after.

Best,
Grady

[TechnoViking]

Hey Grady,

I was planning to go to Pueblo this weekend, but the blown motor has put that on hold. Have fun!

Anyone else out there increase compression by methods 2 or 3?

[wowzer911]

It's common to fly cut the heads for increased compression. Certainly has to be the cheapest.

[javadog]

Anytime you machine something between the case and the cam housing, you are creating problems for the cam chains. Cut enough and the cam chains will be too long. If budget permits, find a set of the Mahle 98mm 9.8:1 pistons and cylinders that were so popular in Europe years ago. Upgrade the cams a little, too. I second Grady's recommendation to twin plug the engine. I suspect gas quality will be an issue in the future. My area is already limited to 91 octane as a result of the price increases.

JR