Jerry Feather

I have read several threads about 968 Pistons in a 928 block bored to 104mm, most commonly with a stroker conversion. However, I notice that the valve relief cut-outs in the top of the 968 pistons are bigger on one side than on the other side of the piston top. So, I wonder how these pistons are usually oriented in the 928 engine. Is any machine work required on the pistons for this installation? Bore the block, of course.

I didn't go back too far in my search, but where I looked said nothing about this question. Of course, I most likely missed it, which I'm sure someone will post a link to show me. But, thanks for your thoughts on this.

Jerry Feather

terry gt

Jerry , 968 pistons need the valve reliefs cut so they are the same size / they may need the tops shaved down depending on the deck height of the block . BUT before you go down that road , I met Tony Ford at the SEAMA show . He is a application engineer at MAHLE Motorsports , they can make a set of new 968 pistons in 102/103 /104 mm with the factory coating to work with the alusil block . He said 250-300 per piston ,and + /- 200 for a set of rings . tony.ford@us.mahle.com hope this info helps Terry

Jerry Feather

Thanks, Terry. That actually helps a lot, boith ways. Jerry Feather

danglerb

Mahle aftermarket pistons have a VERY poor record of performance in a 928.

IcemanG17

JE pistons seem quite successful in strokers.....but the longest living strokers all have factory 968 pistons...

Fabio421

Aren't all/most stock 928 pistons Mahle?


JE pistons require the block to be nicasil'd I believe. I don't think JE has a skirt coating that's compatible with the alusil bores.

Wossner claims to have a skirt coating that is compatible with Alusil and there are a few 951 guys that have used these pistons with success so far. The set of pistons with rings for a 928 is <$2k if I remember correctly. They will make the pistons to whatever specs you wish. The rep for Wossner that I spoke to was Chris White. He can be found here on Rennlist.

928mac

I think Greg just went through all this on another thread.
what was it now .... oh ya it was to do with piston to rod offset on chevy rods i think.
search chevy rod offset and you might find some info on it.

Brad

hacker-pschorr

The issue is with the coating, Mahle has not been very consistent with applying the proper coating when ordering for an Alusil engine.

We have three sets of these. Mahle offered to re-do the coating but none of us are interested in wasting the time / money of building another engine with them. Last time I talked to Todd I think we decided to use them as very expensive paper weights and ash tray's.

If I were to go with a set of aftermarket pistons for Alusil, Wossner would be my choice. They have a much better tract record with providing the proper coating.

Chris White is a great guy to talk to, talk about a mountain of knowledge.

Jerry Feather

I wonder just how worn the coating on the skirts of otherwise good looking used 968 pistone can be to still be servicable in a bored 928 block--alusil. I wonder how I could tell.

Jerry Feather

atb

The mahles are a full skirt piston and will interfere with most aftermarket rods when used in a stroker application. The kolbenschmit (sp?) piston is a partial skirt which will clear most con rods. Don't know if it's an issue on a 5L crank.

danglerb

My 8 are KS, and my understanding is that Mahle that is OEM to Porsche is different from Mahle motorsports.

robot808

Pretty sure Jerry doesn't have to search for that one.

GregBBRD

Jerry Feather

Right, but it was the thought that counts. JF

Tony

I was wondering how long this would take.