965 heads mods

[paganrj]

I have read here about several modifications to 965 cylinder heads. I will like to know which ones have greater impact in performance (based on experience). I have also heard that reducing 1mm from the cylinders will increase compression ratio from 7:1 to 7.5:1. Does anybody know if that can be also achieved by shaving the heads instead of the cylinders? any recommendations?
Regards
R

[fredmeister]

Just remember that shaving cylinders or heads reduces deck height and this effects valve to piston clearance. I don;t know if the turbo has danger in this area like the normally aspiro engines where this is a critical dimension. But something to look at anyway.
I don't know how much margin there is with the flat top pistons on the turbo to the intake and exhaust valves as I have never done a rebild on one yet.

[David]

Cutting the heads or cylinders is not a great idea. You'll have issues with the squish area and with the cam chains which can dealt with but why bother.

The best option is new pistons. I believe the 965 cylinders are fully finned so you could have the existing cylinders opened to 98mm and re-plated. Then you'll want different cams, etc.

[AFM744]

I seriously considered this option. My approach was 1mm off the heads, and 1mm offset on the wristpin bushing for a total gain of 1 compression point. But it opens up a whole can of worms with issues like compensating for chain lengths, cambox seals, manifolds not fitting, as well as the unknowns of valve>then removing the pistons to relieve them. I went with JE 8:1 pistons, and every cold startup my motor sounds like a bag of hammers in a paint mixer, so pick your poison.

[David]

I'm running JE's and I don't have noticeble piston slap. I forget what clearance I have, but I set it the same as the Mahle pistons on EBS's recommendation. What clearance do you have?

[AFM744]

The JEs were definitely smaller than the Mahles. I gave them exact dimensions of my Mahles and my cylinders, so when the custom pistons came smaller I just figured it's the reputed evil of JE pistons. I have the dim's written down in my notebook at home... probably 2 or 3 10ths of a mm. Skirts at wristpin were almost exact, it's the crowns (above the compression ring) that were notably smaller.

[JFairman]

When you say going up "one compression point" do you mean going from 7:1 to 8:1, or do you mean going from 7:1 to 7.1:1?

I cant find an answer to that with google....

thanks.

[David]

I always figured it's one full point as in 7:1 to 8:1.

[AFM744]

Originally Posted by JFairman

When you say going up "one compression point"...

I meant 7:1 to 8:1; that's what I've always heard as "1 point".

[paganrj]

Thanks everybody for the replies, all have been very helpfull!!!!
I will stay out of shaving the heads. Even when I think that the chain tensioners should be able to compensate for the extra chain lenght, cam boxes will definitely create an issue if not modified also.
Any experience (or issues) increasing intake or exhaust ports? other recomendations for heads work?