atb

Need help from the 944/968 crew in determining what I have in the way of pistons. These are all 104mm pistons.

First off, these pistons all appear to be dimensionally identical. Is that the case that the 968 and 944S2 pistons are the same? If not, what is the difference?

Second, I've heard that the 968 pistons are forged, but that the 944S2 pistons are cast. The S2 and 968 Mahle pistons look identical, except that the S2 piston has some machining on the skirt under the pin boss (the motor was rebuilt so probably from balancing) and the S2 piston has a small circle casting on the underside (see pic), which the 968 piston does not.

So, were the pistons interchangeable, and if so which are cast and which are forged? How to tell the difference?

Thanks for any input.

Tom Carson

hmmm...the set of S2 pistons I have look identical to the Mahle 968. Do you know what year 968 they are from?

oh, and bump !

pete944

I really want to know the answer to this too.
This is a pretty timely post, I posted the same question in the "Budget 968 turbo" thread today.

ToxicSlick

I think I remember just reading that the 944 s2 pistons are forged in that article posted in the media section of the 944 fest site. Anyone not lazy could check there, in the part about the s2.

pete944

You're right. In describing the S2 engine it does say "pistons are now forged instead of cast". I'm just not sure if that is completely accurate. The S2 hadn't been released yet at the time the article was written.

mmmbeer

All years of the 968 have the same part#94410305800 pistons according to the PET.

Regards:
Eirik Kvello-Aune
www.944968.com

Tom Carson

but here he says the 968 piston have different weights

https://rennlist.com/forums/showthre...oto=nextoldest

pete944

Surely someone here has a definitive answer on the S2 piston (I know, don't call me Shirley, ha ha).
How do you tell visually if a piston is forged or cast?

PorscheG96

Good pictures, thanks for sharing.

You cannot rely on PET to tell you if parts were updated or changed during production because it will only list the latest/currently available part version. Porsche switched from Mahle pistons in late '91 or so to Kolbenschmidt AG for the rest of the 968 production run.

Basically the 968 pistons [both Mahle and Kolbenschmidt] are forged and the S2 pistons are cast. The Porsche WS manual describes all 944 NA pistons [even 2.7 liter] as cast. Only difference I see in the pictures is that the later 968 pistons may be lower compression. There's more of a bowl in the piston rather than just the valve cuts in the earlier Mahle one.

You also need to be careful with S2 connecting rods. Those are cast while the 968 rods are forged. I'm sure you could use them just fine in your engine but they won't resist poor tuning or high revs for as long as the forged ones will.

adrial

Has anybody ever documented a failure of cast rods? Or does everybody just get the forged because of course, forged is better...but do we know if its really necesary?

iloveporsches

I've never seen anyone documenting the failure. Then again, I don't think I've seen it more than once (someone blew up ona dyno) on RL in the almost two years I've been here.

So it was the 82 and 83 NA's, 86 Turbo, and 968's that had forged rods? And 968's where the only one's with forged pistons?

Matt Romanowski

For pistons, just check under the domes. Any piston with a design / lots of ribs is cast or hypereuretic. Forged pistons have very simple / no design under the dome. Post pictures of the insides and we can tell you without doubt very quickly.

Matt

Tom Carson

dunno about this...the cast pistons I have don't have "lots of ribs"

pictures? have a look at this cast piston:

https://rennlist.com/forums/showthre...hreadid=107282

GoRideSno

Here is a link to som brief info about the KS 944S2/968 piston. PK in the 4th column, bottom of PDF, indicates that they are forged.
HTH,
Andy K

Larry Parker

968 pistons are forged and S2 are cast.... They no longer will produce cast S2 pistons as the forged 968 pistons are there replacment........ I went through this for months when I built my S2 motor.......

There was talk of Mahle motorsport making some higher compresion forged units for the car, but I have been out of the loop snese spring when I sold my car....