High compression 90mm pistons for 2.7?
 

Hi all,

Am toying with the idea of 9.5:1 pistons for my 2.7 rebuild.

Do Mahle have these available, or is JE my only choice?

Do any other makers besides Mahle provide the CIS specific domes?

Many thanks in advance...

EDIT: Do the CIS specific domes still matter if the cams are going to be reground to a 964 profile?

Hi:

Mahle does a small run of 9.3:1 90mm P/C's when they get enough orders to make them. Availability is scattered but I'd check on that with several suppliers to see what is in stock.

JE's are always available in any CR you wish but they certainly do not last anywhere near as long.

Mahle is the only maker of the CIS-specific piston dome configuration. If you use CIS, this is the best way to go, by far. If you switch to carbs, EFI, MFI or whatever, the double valve relief pistons are recommended. Your 964 cams will clear either piston design,...:)

Thanks Steve!

Arrgghh!

Where do I even begin to look for a set of these HC Mahle 90mm sets?

I'd better start emailing some online stores...

There's a "normal" set of 2.7 Mahles at Rennlist classifieds, item 28, I believe.

The 9.5:1 versions were only imported by Andial who are now in the parts business. Give them a call ..... sitting down.

Sherwood

There are definately 2 stock versions of Mahle's that were used for CIS 2.7's. The dome shape is different, and I assume the CR is also different but I don't know for sure. This may be the difference b/w S and Normal pistons, as there is a modest difference in CR.

Sorry, I didn't realize you were initially looking for CIS-type replacement parts, but if you're going to replace your CIS pistons/cyl. and cams anyway, I'd seriously consider switching to carbs unless emissions compliance, modest power gains and factory-stock is high up on the list.

With that decision, it's the same cost to replace what's there with a complimentary set of RS P/C I mentioned earlier + more aggressive cams to make a real difference in the arc of your smile.

MHO,
Sherwood

hi,
really good info here.
http://www.pelicanparts.com/techarticles/911_engine_rebuild/911_engine_rebuild2.htm
cheers

Listen to Steve.

Best,
Grady

Thanks Sherwood.

(Although it might come back to bite me in the rear,) I've decided to try to maintain a more-or-less stock 2.7L CIS.

Bearing that in mind, I guess the standard P&Cs are prob the best way to go;

I've considered the RS spec P&Cs you mention above, but my understanding is that the CIS domes on the stock pistons will burn cleaner than the RS domes.

I'll prob stick with simply installing SSIs/sports exhaust +/- a cam regrind to SC profile for a mild performance upgrade.

If you flycut the heads, won't CR increase slightly? Would it be close to 9.0:1?