Well after much deliberation I went with these forged pistons because I believe that they will wear better than the 2618 alloy.

I installed them with 0.0025 inch of bore clearance as per Mahle's recommendation. Upon the initial start up they slapped for about 15-20 seconds and then quieted down. They continued to slap under cold start conditions (~30 F) for about 5-10 seconds for the first 50-100 miles of engine operation.

Now they don't slap even under cold start conditions. :D

Time will tell if the 4032 alloy holds up better, but there's got to be some reason Porsche goes with these forged babys.

What kind of ring gaps did you go with?

The Mahle's come coated i believe right?

Louis

Keep us updated, i will soon be replcing my CP's with the Mahle's. Hope they are quieter than the CP's

I used Mahle rings, they are a ductile steel--might be nitrided or coated. The pistons come with rings (that has not made it to internet sites yet). They were gapped according to Mahle's specs, which I posted some where here.

There are two coatings on the pistons. One is a phosphate coating over the entire pistion. Like nitrided, phosphate hardens the surface. In contrast to the blinding CP aluminum, Mahle pistion are a dark greyish brown. The second coating is a "Grafel" coating on the skirts which as far as I can tell is Mahle's proprietary name for PTFE (telfon).

Additional thermal coatings can be added to the crowns by sand-blasting the phosphate coating off, and applying the thermal barrier. This is not standard.

bboy,

sweet, my Mahles should be coming via FedEx today and they will go in tonight. I am hoping that mine will be as quiet as yours are. Are you running the pistons in an otherwise stock block or do you have some other aftermarket stuff in the block as well?

Ernie:)

It's got all the goodies. I bored and honed for the proper fit (100 mm pistons), which means I had the pistons in hand prior to boring. If you don't do that, I don't think you can be as sure about noise. At the very least, I'd have the bores and pistons measured by a competent machinist. You'll find that the pistons are very close in diameter, but your bores may not be. At that point you can make a judgement about the clearance that you will have if you put the pistons in to the block.

plus the mahle's are much cheaper considering they come coated and with rings!!

They are less than $500. I got mine from Spokane Speed in Spokane, WA. Suby chrome rings are about $100.

bboy,

hmmm, I didnt realize you had the 100mm pistons. I got the stock bore pistons but they are going into a new shortblock. Well, Ill report back on the noise as soon as the engine is in and running

Ernie

The piston skirt coating is more than likely not PTFE.

Sneak preview from my new Piston FAQ:

1. Dry film lubricants, also known as solid film lubricants, provide a lubricating film that reduces friction, inhibits galling and seizing, reduces piston scuffing, extends cylinder bore life, and in some instances can aid in dispersing heat. One of the obvious reasons for using a lubricating coating is to reduce friction, which improves wear, extends part life, and frees up power normally lost due to friction. A second major benefit is a reduction in part temperature.

Most dry film lubricants are Molybdenum Disulfide based. Why not Teflon? PTFE, also known as Teflon, is listed as having the lowest coefficient of friction (COE). However, under high speed and load, the COE of PTFE degrades while that of MOS2 (Molybdenum Disulfide) improves, until it is significantly better than PTFE. Moly also attracts oil, keeping an adequate film on the part unlike PTFE, which sheds oil.

Dry film lubricants are primarily applied to piston skirts.

Grafel (sp?) is a dry film lubricant and it's applied as a patch on the skirts.

I bored out the block to fit the oversized piston. I think the stock sized pistons could work in a new block, but I'd certainly measure them and the bore, at the very least, just to know and/or report what you find.

In comparison I have CP pistons in my built 2.5L. I had the pistons coated, oil shedder on the underside, non stick on the sides and a ceramic coat on top. I had these fitted with 0.0035 clearance to the original piston size... They do not slap and they are not noisy but of course they were more expensive than the Mahle's. The coating I had done was $35 per piston on top of the piston cost itself. Just wanted to mention that not all CP's are noisy. They are also installed into Darton sleeves.

bboy you need to make it down to PDX and say hello. Jeff S's car is back together with a 50 shot of nitrous, that's going to be fun tuning.... My car needs another 200 miles and then I'm tuning up the boost, I also need to rebuild my JDM 6 speed :(

Yes, I never meant to imply CPs slap and Mahles don't. I know of CPs with the proper clearance and no coatings that don't slap.

This isn't a "which piston is better" thread. CP makes great pistons. The difference with Mahle is the alloy, 4032. It's harder and more likely to handle mileage well IMHO. The 2618 alloy (CP and many others) is more resistant to detonation's effects. Both are more durable than cast pistons.

I posted this info up because I don't know anyone else who has tried these pistons yet.

Update?

I can give a little feedback as I had these put into my new block before it went in. The pistons are absolutely great: no slap or sound whatsoever. As far as I am concerned my motor is indistinguishable from a stock motor in sound and reliability.

ernie:)

Well I can distinguish a sound difference, but they are a different metal. There still holding at 3000 miles and about 450 whp. Just get the p-w clearance right and I think most forged piston can be pretty quiet.

bboy, do u think you can give a full list of what you have in your shortblock?

Hmmmm let's see I've never done this.

Motor:
Drilled and balanced crankshaft a la Axis Racing
Coated rod bearings a la Axis Racing
Oliver rods, lightweight (115 gm less than stock per rod)
100 mm Mahle pistons (0.0025 bore clearance) bored by DG Machine in Auburn, WA
DPR Stage 2.5 AVCS cams (.406 lift, 228 duration@0.050, 110 LSA--required some AVCS optimization from Phil)
DPR conical valvesprings and titanium retainers (really like this design over dual springs)
All clearances and assembly by WorldOne Performance (Wayde Segewa).

Non-motor:
Element Tuning GT65 Turbo Kit with reversed intake manifold (very trick!)
Espelier Exhaust
TSX front mount
Turbosmart EWG + e-Boost2 controller
Element Tuning Hydra

Still working on water injection integration with the Hydra. It's more complicated than it looks and the higher you go in boost the tougher it is to get water in the intake tract. As soon as I get this dialed in, I'm hoping for 500+ whp on pump fuel.

Someday I'd like some of those Cosworth CNC heads. Also someday I'd like to plumb the front mount IC like AlanG did. Phil (Element Tuning) get's more power out of a larger compressor wheel with nearly the same spool up. If someone invents a variable turbine to improve spool up on my turbo (eyes new 911 with gasoline variable turbine), I'd buy it immediately. Mind you I'm not complaining. 15 psi at around 3500-3600 (4th gear) is pretty responsive, but I'm greedy. :D

wow man thats an awesome setup you have there.

:eek: that thing sounds like a beast.

do you have a link to some pics of the motor?

it's good to hear they are still holding strong after 3k miles

WorldOne had one posted at one time. Let me look.....but the turbo was not in yet.

http://forums.nasioc.com/forums/showthread.php?t=885607

The intake tubing has since been mod'd for two water injection jets. You can see the turbo out of the car there. It's a GT35 compressor wheel and housing. The CHRA is journal bearing, and I don't know what the turbine and housing are.

The car looks remarkably stock. You'd never know it could beat up on 911's and Ferraris.

what is the advantage of running reverse intake manifold?

Also if you reverse the intake manifold can you keep the AC compressor?

I can give a little feedback as I had these put into my new block before it went in. The pistons are absolutely great: no slap or sound whatsoever. As far as I am concerned my motor is indistinguishable from a stock motor in sound and reliability.

ernie:)

Did you use the 99.5's or the 100.00's? If you used the 99.5's, did you hone the block?

You can keep the AC compressor but it's not easy to do. Search for the "reverse AND intake" in the 2.5 forum. The problem is not the belts, which can be worked out, but getting the intercooler tubing to fit while making the turn toward the throttle. You also might have to do some grinding if you rotate the TB as I did so that it does not impinge on the AC compressor.

I used the 100 mm pistons and bored out my used block. If I had a new block, I might have been able to get by with the stock hone, or been able to hone slightly and use the 99.5 pistons.

FWIW: It turns out that boring and honing a Subaru block is not straight forward. If you look down into the cylinders you'll see some braces. Those prevent most boring machines from working. You can skip the boring and just hone a lot instead or find a shop with boring equipment that will work. Choose a machinist carefully. They are not all good. Talk to engine builders with known reputations about who they recommend, and if need be mail the block off if you can't find a local shop. Seattle is blessed with lots of disgruntled former Boeing machinists.

Thanks for the info but i just wanted to ask again. Whats the benefit of running the intake reverse. Im assuming since the intercooler piping is shorter it will reduce lag? Anything else?

Shorter hosing to improve responsiveness, and it looks cool. I got rid of about 3 ft. of tubing. If can re-do the other side, I could lose another 4 ft. or more.

how much advantage do people think there is to ceramic coating the crowns of these? I called mahle and was told they do not recommend it..... tks

I think that if you are going to go below Mahle's recommended bore clearance to say 0.0015-0.0020" that a thermally reflective ceramic coating could help keep the skirts cooler and give you some insurance. I looked into this, and the rule of thumb was that with a crown coating could shave 0.0005 (that's 5 tenths of a thousandth) off of your clearance, but no one will guarentee that adjustment.

If you are going to apply a ceramic coating, or any coating, you'll need to blast off the phosphate coating that is already in place on the crowns.

Thermal barrier coatings in general are supposed to make the engine more thermally efficient, but maybe the money is better spent getting more air in the chamber to make power.