Ian928

I am in contact with a guy that has 8 new oversize Wössner pistons for the 928 for sale. These were ordered for a 928 Turbo project, but the pistons were delivered very late and the owner found another solution and do not want the pistons. The seller was the importer of Wössner piston at the time and got stuck with the pistons. This is the information the seller has given me:

Piston diameter: 100,43mm (for 100,5mm bore)
Compression height: 40mm
Volume in piston: 36ccm
Ceramic coating for the alusil block on piston skirts
Bolt and clips but no piston rings
Price: 8000NOK ($1150)

I believe the importer was screwed, the 928 has 42,5mm compression height, my guess is the engine builder used 944 specifications when he ordered the pistons and when he noticed the mistake he used the late delivery to get out of the problems.

36ccm volume in piston will give a compression of about 8,3:1 for a 928S4, I do not know if this volume is good for any 944 engine. I know the Turbo use the old two-valve head, but what about using these pistons in a 944S engine with turbo maybe?

I have nothing to do with the seller or the product, I am just passing this information on to fellow Porsche fans. If somebody is interested I will link to the ad (witch is in Norwegian...)

fast951

It looks that the compression height is a bit shorter than what it should be for the std 2.5L stroke. Maybe a typing mistake.

A dish size of -36cc will give you a VERY low CR with a 951 8V head. Might work on the 16V head, but additional calculation is needed.

Ian928

All 928's with 100mm bore has 4-valve heads so I am pretty sure these pistons do not have valve pockets for 2-valve heads. The seller also told me they did not have much squish area, that would be bad for the 2-valve head.

I checked the spec for the standard 944 turbo (my girfriend owns one), and I believe the volume in the piston on a standard 944Turbo is 25cc? If that is the case, 36cc is way too much. I started thinking about the 2.7 944S though, this is a 100mm bore, isn't it?

Might be a nice upgrade to use a 944S engine with forged pistons and lowered compression in my girlfriends 951?

fast951

Ian,

The factory 951 pistons have a 25-26CC dish. The 944S is not a 2.7L engine, it's a 2.5L 16V with 100mm bore. These Wossner pistons "might" work on it. As I mentioned additional calculation is needed. I assume you want to turbo charge the 2.5L 16V? Also, double check the Compression Height, 40mm is a bit short for the 2.5L.

If you can make these pistons work for you, the price is great! I wish they were for 104mm bore, I'll pick them up.

Ian928

John,

Thank you for the info, my girfriend has a '89 951 that has the original engine in it. It has some miles but there are no signs of problems yet. I was just thinking IF she needed to overhaul she might as well look into this. I have no plans as for now to do this however, I just want to help the seller and you on the forum to get in contact.

Regarding the compression height, I was told on the 928 forum that 40mm was the compression height on 944's, but if that is not true, these pistons are probably only usable as ashtrays (unless someone want to machine their blocks...)

Raceboy

Or to use with custom rods, thus increasing rod length and improving rod length/stroke ratio.

Tom M'Guinn

My Mahle/Andial 104.5 turbo pistons had 33cc dishes, for what it's worth.

Ian928

Thank you, and this is a 3.0 with the 2-valve turbo head?

JohnKoaWood

Damn expensive, allbeit nice ashtrays..

Olli Snellman

Wössner usually have ferrostan coating, like oem ones have.

Ian928

Good point! And that makes them possible to use in a 928 also, the 33cc bowl is perfect for a 928S4 with boost. Of course, you need 8 custom rods at a considerable cost to do it, or maybe a stroker crank with 2,5mm longer stroke.