DANdeMAN

No, 85-86 are S3.....

GregBBRD

Mark:

944 S-2 Pistons, not 968.

mark kibort

Then I dont get it. (edit: I get it .GB was talking about S2 as in 944S2! )

what are those center pistons if they are not 968? Oh, are we talking S2 944? I seemed to remember that there were 2 types of 944 pistons that were used in 103mm applications. 968s and 944S2?? but I thought the only 104mm piston was the 968 becuase of its 3 liter motor. something like that?

edit: thats right. the 944S2 was the 3 liter 4 valve , 104mm pistons while the 968 was also 3 liter 4 valve. But, the differences must have been in the valve size. thats why you have to use 968pistons if you are going to use the bigger valves, where 944S2 are more like S4 sized?

mk

mark kibort

I just got it!

thats why S2 and 968 pistons can be used, right. which are better? is the shape of the piston different , or is it just the valve reliefs?

thanks

Dennis K

Greg -

What's the identifying characteristic that makes them 944S2 pistons? I've never seen either 944S2 or 968 pistons in person before, only internet pics such as *edited*Adam's:

Hilton

The skirt is different - there's an old thread somewhere where Erkka was explaining the difference between the two brands found in 944S2's and 968's.

Dennis K

Brian - yes, 968 (944S2?) pistons, GTS crank and custom rods but you know Jim, displacement is yet to be determined.

Sterling - I think they're ~400g. Don't know the material.

heinrich

Those are not 968 pistons????

Hilton

This thread is the one I meant with Erkka's posts on the variety of piston types.

https://rennlist.com/forums/928-foru...2-pistons.html

edit: Just spotted Dennis' post with pics from it above..

atb

That pic above is mine guys. I didn't remove the pistons from the engines, (except the S4 ) so I can't guarantee that they are from the engines that I labeled them from, these are the engines that they were represented to me to have come from.

jleidel

Dennis, where did you source the 968 pistons from? I'm looking for some 104mm pistons for a high revving motor in the works.

GregBBRD

The skirt design is indeed the difference. The 968 pistons have no skirt in the area below the pin, where the 944S2 have a complete skirt the entire way around the bottom of the piston.

Porsche actually list 3 engine types that use the 104mm piston and I believe you will find that the 3 different piston designs and manufacturers will be found specific to these different engines.

In a stroker engine, this skirt piece gets into the way of the counterweights and can touch the very bottom of the cylinder bores....where the block re-inforcement area is 90 degrees from the bore. The 968 design allows a more generous counterweight design and eliminates the problems at the bottom of the bore.

If you are going to use a "shorter stroke" than 95mm, or so, the differences in the design will probably not be an issue.

danglerb

Here are a few picts of one of the 968 pistons I recently bought, note the K with S over it in the first pict lower right. My 99 cent caliper measured the top as just under 104mm, first time I opened the box was now, still haven't looked at the other 3, and still looking for 4 more. I'll pass on the info on any extras I find.

AO

atb

So if I'm understanding Greg's last post, he's saying that only the Kolbenschmidt pistons were used in the 968's and not the Mahle's?. Is the piston pictured in the middle of the bottom row of the posted pic mislabeled as a 968 piston?