The 951 pistons have a much deeper bowl than the 968 pistons. But I'm surprised that it's only cut out for one of the two valves in pair?

 

Yes they do, but I am talking about total valve travel. See the photo of the 1st post in the thread, the valve reliefs are cust exactly at the depth as they are on the 944 S pistons. And I did not measure the relief depth on the piston itself, but used a fixture that gave me absolute valve travel, not related to piston.

951 piston has deeper bowl, but it is smaller and the valve reliefs have to be made at the edges of the bowl, not inside the bowl.

 

No 16 valve head; stock 8 valve Turbo head with slightly larger exhaust valve sitting much higher in the valve seat. Sorry for the confusion. Mike

 

Just realized everything was off compared to the 16v pistons/head so that makes sense

 

I was going to mention that yesterday that this looks like flycutting for 8v.

 

So, does anyone know how much piston material is this area? I want at least .080" additional clearance from where piston and exhaust valve are closest, wherever that may be. Thanks, Mike

 

Here is some informations on stock pistons tickness:
https://rennlist.com/forums/944-turb...in-w-pics.html

 

With respect to total valve clearance, do you have any numbers available for how deep the valve was in the head with the cuts in the 951 piston giving equal total valve travel to the 16v piston? I guess what im asking is, once you finished cutting the 951 pistons, how much of the S2 valve stem was left sticking up from the fixating guide? I'll be using normal S valves but I'm assuming I should use the same depth. Out of curiosity did you ever consider machining the pockets deeper to achieve a non interference fit? Is there enough material on the piston crown for this to even be possible?

 

I did not measure the absolute depth, I just focused on getting the equal. Never considered making them non-interference as that would lower the CR too much and also create nasty hotspots during combustion.

 

Do you know how deep the STOCK 944S/S2 16v piston notches are?

 

I’m in process of building a 2.5 16 valve turbo motor and have both S and 951 pistons not sure which way to go take a 1mm off the outer crown 360 deg on s units or cut valve reliefs in 951 unit. The S piston is a tiny bit lighter so thinking of getting them cut then swain coat and put them back in there holes they came from? What’s the feedback like on the 951 pistons running?

 

Attachment 1351909

I left the valve reliefs as they were and removed 1mm from the rest. Much less work this way.

 

Are you already running these...? Is engine performance equal to your expectations..?

There's definitely room in the piston design to take off 1mm...., I think the thickness is 6-7mm, at least to the ring land.

Just curious, because, you have increased the squish area that directs fuel/air towards spark and valves to .080" assuming 1mm head gasket.

T

 

I am, I have around 5000km on them in less than half a year. It's the first 16v pistons i've had, so i don't have anything to compare the performance to, but i'm very happy i went with these. I'm also quite conservative with my CR, running a 1.9mm Cometic.

 

Guys, I'm bumping this thread to ask if anybody else is going this 2.5 liter turbo route.

Reason being, I have a set of custom 100.5mm forged 4 valve pistons with reliefs designed for the use of the 39mm 968 intake valve. (any S/S2968 intake valve will work with these)

These were spec'ed for an NA engine but Wossner got the dish volume wrong at -22.5 cc and I got stuck with these at a $1136.00 price tag.

With the .050" cometic gasket, these would yield around 9:1.

Willing to make a killer deal on these, pistons, pins, alusil/steel/nikasil compatible rings, they have the added alusil compatible skirt coating.

Pistons were spec'ed and lightened 30 grams lighter than the factory cast KS piston/pin combo during manufacture by Wossner..

Pics on request.

Make reasonable offer.

T