2.4 CIS Piston questions
 

I am about to embark on a rebuild of my 1973.5 911 T numbers matching engine. My previous rebuild left me with high oil consumption and leaks. This time I plan to have it done professionally. I feel that I likely will need new pistons/cylinders. Anyone know of a set? I have found 2 different parts numbers for the Mahle set listed, but NLA. The two numbers I found are: 911 103 940 02 and (USA) with an 01. My car was a USA version. Would there be a difference? If original sets are unavailable, what are my options?

Any help would be appreciated!

Thanks,

Alan

Alan,

These 85mm CIS P/C's are still available, but only through Porsche and damned expensive.

Trouble is, thats what you need since the non-CIS pistons do not run correctly in these particular applications.

Steve
Can you elaborate on the piston issues with CIS and differences
Thanks
Frank

2.4 cis
 

Hi,being that it is a 7R case it is easy to just open it up to 2.7 specs.2.7 parts are a lot less money than 2.4 CIS.Fred

Wossner makes 2.4 pistons in 84 84.5 or 85mm diameters.
Only thing is they will bump compression to around 10-1.
But that should always be measured-there can be variables.

The '73 CIS engine had the smallest intake port of any 911 engine, 30mm. You can't really open 'em up because the steel intake runners are the same ID, therefore you'd be hard pressed to make the 2.7 CIS pistons work for the engine to breathe properly or efficiently. I'd stick with the stock CIS pistons, if the grooves are still in spec, and get some new AA cylinders. My $.02

What Steve said.

You want the bowl shape dome for CIS.
If 2.4s are unobtainium (and your pistons are not reusable) i'd go for 2.7s

Does JE still make custom CIS Pistons? Go 1mm over and bore your current cylinders to match. I can't imagine it would be any more than other options. Punch up the compression to 9-9.5, throw some 2.7s cams in. Should be a fun 2.4+.

If you really want 2.4CIS pistons, they do come up from time to time and don't really demand a premium. Maybe keep an eye out for a used set.

If you have a matching engine, don't even consider punching out the spigots. There are several ways to get back on the road without ruining a matching numbers case.