Charles A. Toupin

From the numerous conversations I had and with the reading I did on here, my understanding is that any piston can cause an engine failure if the job is not done properly and up to the specs, even stock ones. If everything is done properly, any type of pistons will last.

So they are probably more or less the same interms of durability. So the other very important part is the block itself, whether it be an Alusil or a steel sleeved one, although the steel sleeved ones are easier to work on.

Am I correct?

C.

Chris White

I wouldn’t say that the steel sleeved blocks are ‘easier’ to work on – they do give you a wider choice of rings to use and they are much more resistant to damage from detonation or contamination (very hard to score a steel sleeved block).
The other benefit of the steel sleeves used to be that you could any aftermarket piston, now the Wossner is making custom pistons for the alusil block it is possible to get any design for the alusil blocks that benefit of the steel sleeves is not as great as it used to be.

As for the first paragraph – yes, as always, if you do it wrong it will fail! More pistons / blocks are ruined by miss tuning that assembly….!

Charles A. Toupin

Thanks for the info Chris!

C.

Fishey

Our J&E Pistons on a 3.4L 911 cracked around the wristpin and its without a doubt a flaw in the piston design. When we called them J&E seemed to be very aware of the problem.

Tom M'Guinn

I originally bought a set of those pistons from Tom C., but ultimately opted to use Mahle pistons instead. I was not comfortable that the coating was truly Alusil compatible, since it was a non-iron based dry film lubricant. I went with Mahle's because they have a long track record of success. To me it's false economy to buy cheaper engine parts in hopes of saving money. The relatively small amount saved is dwarfed by the cost of starting over if it fails.

95ONE

That's what it was.. I couldn't remember. It was the coating..

And here is the story that Richard Jackson had about them. Its a 50/50 story from what I could tell.

https://rennlist.com/forums/944-turb...=piston%2C+tom

George D

Since I'm in the process of installing new pistons. Chris White hits the nail on the head when he states improper tuning is the culprit to most damaged engine builds. My motor was running lean on the number 4 cylinder. There was detonation on number four only. I didn't hear it. This caused the cometic gasket to allow exhaust pressure into my coolant (leaded into the coolant). This caused more heat related issues that were very noticeable when we pulled the head. I decided to just replace all the pistons, main bearings, rod bearings, and basically start over. I could have just replaced one piston and been fine, but I wanted this motor to be done correctly. I will be installing JE 2618 pistons into my Nikasil or NiCom block. We coated the pistons for better oil absorbtion and easier break-in. We could have used anything, but Garrity had these on the shelf. He has used these in many 951 motors with great succuss with zero issues. He has some of his Audi clients running 1000hp on a bored 1.8 turbo motor. Granted the blocks split after 25 to 30 passess, but the pistons hold up. But then again, so would other 2618 forged products designed for this particular application.

Most large forged piston manufacturers build similar products. They may look a little different, some are lighter, some have shorter skirts...LOL, but all are made within similar standards. I understand that the 944 series motors have unique issues when using the factory bores, but there are plenty of properly coated pistons from many manufacturers running well in our cars.

Here is a good post:

Forged pistons, barring unique manufacturer’s specifications, generally use two aluminum alloys, which are 4032 and 2618. Typical recommended applications are as follows: 4032 is a durable and lighter material usually used in naturally aspirated engines. 2618 Alloy is designed for the rigors of blown, marine, and nitrous applications.

4032 pistons will have quieter cold start operations due to their tighter piston to wall clearances compared to 2618 pistons. This is due to the 15% greater thermal expansion seen in the 2618 alloy. 15% may seem like a lot, but do the math. Considering a piston to bore clearance of 2/1000's of an inch, 15% is only .0003". Once the pistons have reached their operating temperature, the noise (piston slap) differences should be nearly identical in volume between the two alloys. 4032 pistons will have reduced oil consumption and longer ring life compared to their 2618 cousins due to their better cold start tolerances. While to many these physical comparisons point towards 4032, you must understand that 2618 pistons, for their slight “defects”, are clearly superior in terms of tensile strength and fatigue endurance to 4032. This is why most piston manufacturers specify the 2618 alloy for use in Subaru (turbocharged) pistons.

Duke

There's no doubt the 2618 are stronger. But there's always an even stronger alternative available no matter the part of discussion. So the question is, are the 4032, or stock, pistons a source of failure due to weak material? I would say no. Rods might break, piston coatings might not work, clearances might be off, siezed or galled pistons etc. all of that is common stuff. But I can't say I've seen any of these pistons break due due to the material being too weak.

Tom M'Guinn

Wow, sorry to hear that. Hope things turn out better the second time around.

George D

Duke,

This may be true, but my last set of Ross 2618 forged pistons didn't have any piston slap at startup. We did see some bad scoring from the detonation at number four, and don't know if a 4032 alloy would have fared worse. We don't run 45psi boost like some of the EVO, Subi, or VW/Audi folks. I suppose 4032 is fine for most 951 applications. We chose to use the stronger alloy. It didn't cost more, so why not?

Here is a quote from Mahle: 4032 is a high-silicon, low-expansion alloy. Pistons made from this alloy can be installed with tighter piston to bore clearance, resulting in a tighter seal with less noise. 4032 is a more stable alloy, so it will retain characteristics such as ring groove integrity, for longer life cycle applications. Relative to 2618, 4032 is a less ductile alloy, making it less forgiving when used with boosted and/or nitrous applications.

I'm fairly hard on my "motorsport" vehicles. I like the boost. My sporting vehicles see much more maintenance than my daily driven vehicles. My daily cars are all Toyota/Lexus reliable, comfortable, and plain. The LX sees some hard offroading, but it's still mechanically completely stock, cast pistons and all.

I figure that when spending money on a build that you plan on abusing, why not use the material that is designed for some abuse.

Many of the aftermarket turbo piston manufacturers will not use 4032 alloy. I think we've come a long way with coatings and design to help with piston slap issues. Just warm up the dang car with the stereo going. You won't hear a thing....LOL

George

George D

Trust me Tom. I was just going to drop in a new piston. There was serious detonation at number four. The rod bearing was looking stressed. Then I was worried about the crank. We only replaced the pistons and bearings. I did send the block back to US chrome for a hone. They did it for a few bucks, and said everything was perfect.

The crank was out of spec, and we had it rebalanced and polished.

I want a reliable motor with a perfect tune. This is what I'll have this time around. I've got an experienced TEC tuner. Chris White is going to help us with the base tune, and give us feedback from the datalog. I won't abuse this car till we have a perfect tune this time around.

Regards,

George

George D

Tom, also the knock sensor wasn't wired into my TEC. I did not know this. Not that this would have been a cure, but I would have noticed the TEC pulling timing and would have suspected something.

I also didn't know that you can tune each cylinder with the TEC. Something was messed up with at the number four cylinder. What shocks me is that I didn't hear anything. I've heard 951 detonation. Lesson learned.

We are also installing additional heat shielding and building an intake that will begin in the front driver wheel well. No more hot air from the engine bay.

This is going OT.

Charles A. Toupin

Nice and valuable onfo for me guys

My next block will be one with steel sleeves. I guess it's a little bit different than with the alusil block. So if I ever go with the set of ARIAS pistons and the appropriate squirt coating, the preparation of the block will remain the important factor regarding the reliability. Since I will never run more than 18 lbs of boost (in race conditions), I'm only asking for 3 to 4 years of DE and racing (18-22 days a year).

So that was the coating that was not appropriate (or the preparation), not the pistons!



c.

Tom M'Guinn

If you have steel bores, I'd say you're better of going with a more common piston/ring (JE, Weisco, etc.). If you have stock alusil bores, I'd say you're better off with an iron-coated piston made for Alusil (Mahle, Wossner, etc.). Just my two cents.

Charles A. Toupin

Thanks for the advice Tom.

For the moment, I'm still undecided with my engine rebuilt. So I'll you guys tell what I'll do later on!

Tx.

Charles