Jim Nowak

Is the engine sleeved? If not, what type of coating did you use on tthe JE pistons?

slate blue

Jim I won't answer for Alex however I can say when I asked JE pistons about some pistons, they offered me a coating to work with that surface. I can tell you and have posted before that you need a metallic coating to work over time. You can also get them hard chromed. I think that optn with a slippery coating on the skirts would be quite risk free. That would be affordable also, if you wanted the top of the range coating, you might consider a metallic DLC but at a considerably higher cost.

stvracing

Swain Tech in upstate New York also does piston coating. Great work and great prices.

Jim Nowak

I tried the JE pistons with a hard chrome coating but did not have any luck. The engine failed in under 2000 miles.

stvracing

Jim are you talking about the piston ring coating? If so you need to run either a gold plated or titanium plated ring on Nicosil bores.

Jim Nowak

No, the piston coating. We have have Alusil bores in the 928.

stvracing

I stand corrected on that. Its aluminum/silicone base now I see the reason for the Chrome coating.

stvracing

Why did Porsche go with such a soft wall rather then hard wall soft piston/ring combo?

slate blue

Alusil is even more popular today, I have to say I like it, in the current issue of Race Engine Technology. "The piston rings only contact the silicon particles, producing a number of benefits including- but not limited lower heat retention, improved sealing and better dimensional stability. This is in part to the fact that there is no differential in thermal expansion between block and liner to be accommodated.

New abrasives have been developed to hone this material whereby 0.5 of a micron is removable accurately and out of roundness is is of no issue, where it could be previously.

Also people shouldn't think of alusil as soft, aluminium is soft but silicon is very hard and that is the reason it needs chrome rings.

Jim Nowak

Alusil is very durable. The need to have the coating is due to the fact that you can't run similar materials in a bore unless one is coated. In the Alusil bore, you need to coat the pistons. Nikasil is used on the bore instead of the piston.

Rob Edwards

I'm by no means qualified to disagree, but AFAIK there's no gold or titanium on the rings in my Nikasil'ed motor.

Alex, did JE offer what sort of coating is on the skirts of these pistons? You know as well as anyone here that any coating that will let aluminum slugs live in an Alusil bore for any significant time is a bit of a holy grail. Understood if it's proprietary.

slate blue

I think what racer is talking about is titanium nitrite, this is gold in color and it is very hard. It is used by various NASCAR engine builders.

If JE have a coqting that is great but I don't think it is all that complex.

Strosek Ultra

Are you running a GTS crank? What rod bearings do you use, the stock/Glyco white bimetal bearings or an upgrade like the Clevite H-series or the ACL race series trimetal bearings?
http://www.aclperformance.com.au/Toy...TEBearings.htm
http://www.aclperformance.com.au/For...thBearings.htm

The only piston coating which seem to work 100% good in an Alusil bore is the Mahle Ferrocoating as used on the stock pistons. The optimum is to have the cylinders Nikasil coated or sleeved which make it possible to run any custom made uncoated pistons.

Ake

stvracing

Thank you guys for clearing that up for me.

123quattro

Alusil is not soft by any means. The surface hardness is above cast iron. Thus the need for weird unobtainium aftermarket pistons.