Tom M'Guinn

Alusil cylinders call for pistons with iron-based coatings, like the original Mahle pistons. Purportedly, the original process used to iron-coat Mahle pistons was deemed bad for the environiment, so the process is no longer used. That's most likely what ehall was referring to. It's much like in California, where they are quickly outlawing most traditional forms of car paint due to environmental concerns. The good news is that Mahle now has a similar coating called "Ferroprint" which is an iron/resin coating designed for Alusil bores -- and environmentally friendly.

While the original 2.8 Mahle stroker pistons are hard to find, it is possible to order Mahle pistons and spec them to order. Ski had a set made a while back, and I recently had a set made working through Heritage Motorcars. This way you can also move to a "slipper" skirt design instead of the older factory (heavy) full skirt.

I have owned a set of Arias pistons for the 951 and was not impressed with their quality. Also, the coating contained no iron and so I viewed it as a gamble for an alusil block. I put JE and similar pistons with non-iron dry lubricant coatings in the same camp. I know some people believe they work, but most are still experimental in an alusil motor (in my opinion) and raise the risk of galling and clearance conundrums. If you want to use those kinds of pistons, I'd follow George's lead and Nikasil coat the bores.

Also, unless you are running in a class with a size limit, I'm not sure there is much sense in building a 2.8 over a 3 liter these days. 104mm blocks are cheap, and if you don't want to put money into a 2.7 head, you can have a 2.5 head modified to fit the 104mm block.

Darwantae951

Seeing as everyone pretty much says to "Talk to Chris White" I'll go ahead and post a link to a thread where he talks about the differences between Wossner and JE specifically, and where I pulled that photo from.

http://reutterwerk.com/forums/showthread.php?t=24467

Good info for piston choices, and Chris is usually more than happy to answer any questions people have for him.

ehall

Okay. I figured I must have just misundersttod. Thanks.

George D

Stock 968 piston on left and JE piston on right. If you can get the Mahle, that would be what I would do based on YEARS of proven reliability with our stroker motors using the stock bores. JE told me their tough skirt process is similar to what Mahle does, but I don't have any experience with these.

944CS

Mahle Motorsport would be the best from an engineeering standpoint...you can get a 4032 or 2518 based piston from them (they don't call it that exactly because Mahle has a special refining process for it's Al), but you will pay.....over $200 per piston and 6 week lead time. You can spec any compression ratio, valve size, valve relief, pin placement. The only reason these are not more popular is the cost.

Personally if I were doing custom pistons, I would also do custom longer rods as the 2 valve head does not fill the cylinder as fast as say a 4 valve head, thus you want the piston to spend as much time at or near TDC as possible - a longer rod achieves this.

If using a bare Aluminum piston skirt then you must sleeve the block - use a flanged sleeve - this will give a tougher wall anyway which is desirable for high power applications. Ring life will be comparable to an Alusil bore if the machining is done by a real professional.

944 turbo cabrio

Now I am online again and can see that I received lots of valuable information here.

To make my aims more clear I'll describe my plans:

I am building a stroker because I happened to stumble over a crank and spare block for almost no money and as this also seems for me to be the easiest (for sure almost no machining which I don't have easy access to :-( ).

I will install in a daily driver Cabrio that is also used for trackdays - I value response over high end output.
I will if possible raise compression to 8.5:1 in order to reduce lag further.
Other info: LR or Rogus MAF will be added with full 3" LR exhaust, 55" injectors and Turbo will be LR Super 53 that I also happened to find cheap from a stranded project. Rods are standard length rods from PPM in Australia - they are very light :-)

Bores are all standard with almost no wear.

My aim is in the area of genuine 350 - 375 reliable horsepower.

I have so far found LR the most informative place as regards pistons but as I am tight on budget I need to be sure to buy right first time as I espect to buy in the US but furthermore need to pay transport and customs when items arrive in Denmark.

So far it seems wossner and Mahle are the best options with Mahle probably not wanting to produce a special 8.5 ccompression to me for reasonable money. If I could find Mahles for 200$ then that would be an OK deal for me.
Woessner can make what I need for reasonable money - if Mahle can't be found then I will put my money in the woessner camp and hope for same good results that others have achieved :-)

Wish you all a nice evening - clock is now 0:00 hours in Denmark and I need some sleep :-)

schip43

Hmm, if your goal is 350 to 375 hp? I'm thinking a 2.8 is wayyyyyy, overkill? Pretty sure bolt on's will get that?

333pg333

Couldn't you just order a set of Wossners in the configuration that you want and from somewhere closer to home?

piperporsche180944

I am running J&E Pistons and I really like the lighter internals in my 2.8L. It revs up way faster than the stock 2.5L, I really love the torque it offers at the low RPM's

Darwantae951

A 2.8 would allow him to reach his levels at lower boost, with overall less wear/tear on the engine. At least that would be my guess. Also he wouldn't be that bad off boost with the larger displacement.

+1. Wossners should have a distributor closer to you, I would think.

ehall

I'm just wondering how well a 2.8 will handle higher compression. The 2.8's I've seen in the past were fairly touchy about boost and more compression sure wouldn't help that issue.
Again, I'm just wondering. I don't claim to know.

Adonay

@Duke :

Were did you buy your Wössner pistons here in sweden\scandinavia ? I am also going the stroker rute like "944 turbo cabrio" is a project that has been ongoing for 2 years but still yet to get any pistons. When you order pistons i see there are different cc "bowl" what does that meen ex 20cc and 25cc? compression ratio?

I have been told that the stroker engines do not like very high rpms. I have seen from other cars that boost does not seem to be a problem with the right fuel and timing. But don't quote me on that i am no expert .

@944 turbo cabrio
What engine management will you use for your stroker engine ? A stroker require different timing so a normal 2,5l chip wont cut it.

schip43

Hmmm sounds like you should know...


https://rennlist.com/forums/944-turb...potential.html



I still think for his stated power goals a stroker is overkill?

ehall

rlm328

I wouldn't mess with the copression ratio. I am getting 355 hp / 375 ft lbs torque at the rear wheels on a hot day (100 f, we were pouring water on the intercooler between runs and it was steaming) with 15 psi boost. I have the limiter soft set at 6500 rpm and hard set at 7000 rpm. It is running pump gas. Most of the strokers have a minimum boost that they like to have to really out perform the other motors. This one is 15 psi, the last set up was 16 you will need to play with it to determine your best set up.

A aet of Mahle pistons are going to cost you in the range $1,000.