BC

Very good deal when you factor in the custom aspect of the pistons. Any compression you want. The skirt coating is approved for BMW's version of alusil by the factory, and they are actively working just fine in many Porsche alusil bores.

The other options are still much more expensive, either with JEs (1000 for a set) + the required options of:

Nikasil bores (1800)
steel liners (2500 and up)

The nikasil bores do not add strength, only the ability to run aluminum uncoated pistons which are forged.

The contact for this is a great guy named Chris White. Of 951 prowess and fame.

Thread with pics:

https://rennlist.com/forums/944-turb...th-piston.html

(post 28)

Just thought I would spread the word. 1700 for pistons is alot, relative to chevy stuff, but its NOT when you factor in what you would need to do (most believe) to run ANY custom, forged, uncoated piston. Its also cheaper than the mahle motorsports pistons, wherever they may be and whatever stratospheric funds are required to buy them.

Dennis K

Very cool. Any idea what these weigh? (typical 100mm piston)

Chris White

I’m shooting from memory, but they are about 100g lighter than the 951 pistons.
I have the drawings for a set of 106mm pistons for a 3.1 liter 951 in front of me – they weigh in at 521 grams.

BC

Thanks for coming over Chris. Lighter is usually better. I believe that the 951 piston is heavier than the 100mm 928 piston (cast).

Vilhuer

S4 piston weight tolerance is 761-769 g but that includes wrist pin.

What we need is 103mm 968 style non full skirt piston which has compression height designed for 95.25mm (3.75") crank and either 5.85" or 6" rods. 6" would be better if rings can be made to fit in so short space. I think this would be ideal setup as it would allow many more blocks to be used in stroker builds than what has been possible up to now. I'm willing to bet quite a lot of $ that practically every stroker engine made after day these were available for $1700 would use them instead of used 104mm 968 pistons which are hard to find. Please make these ASAP.

Vilhuer

And we would need two versions of these, 8.5:1 CR thick walled and 11.5:1 CR thin walled for boosted and NA applications. Both with 39.5mm on all four valve cuts.

Chris White

The Pistons I get form Wossner are custom made, so anything is possible, if you can come up with the spec / application I am sure that it can be manufactured.
The rings can fit in a fairly small space – the 3.0 crank (88mm) in the 944 family does not leave a lot of room for the ring pack!
If you want to order a set we will get the engineering drawings done, review them with you and then get them manufactured. I have done a lot of different permutations for the 944 applications – 100mm to 106.5, 8v and 16v, compression ratios form 8:1 to 10:1 (higher is no problem – but I do mostly turbo applications!)
BTW – if anybody wants some used good condition 968 pistons I have some of those sitting around here somewhere!

Fabio421

This is great news. Thanks for posting.

123quattro

I wish there were more threads like this on this forum...

mark kibort

now there is no reason to nicasil, right? you can use stock 928 rings or 968 rings if you are doing a bigger bore. interesting. The question now would be is this coating as good as the 928 factory pistons? Didnt devek use a coating with their stroker engines? those seem to be working ok, right?

hacker-pschorr

Not exactly - nikasil still has it's own unique advantages. But that's for a different thread.

mark kibort

I heard maybe one of them was that it does make the wall surface indestructable, even though they are not structurally stronger. So far so good with the Nicasil block you guys built for me. 9 race days and all seems to be good!

mk

Vilhuer

Unfortunatelly this is too late for my own build as block is already bored to 104 and 968 pistons are ready but there might be few other projects which could use 103's. If coating works and suitable size rings are available this is by far best way to do 6L+ engine. I'll have to get back to you on this later. Might take year even but eventually these eternity projects will move forward.

IcemanG17

WOW 106.5mm pistons....that would make nearly 6.8L with the standard stroker crank!!

largecar379

106.5mm is too big on a 85/86 block (thickest wall block)......according to Reynolds, you want to have at least .125 wall thickness. you can barely do it with 106mm, and then you need to be concerned with core shift.






--Russ