Mike S

I had my stock pistons coated by HPC 5,000 miles ago during my rebuild. I'm about to open it up to redo the head gasket since I'm leaking a tiny amount of coolant from the water passage near the water neck. If I don't see coating there I'm not gonna be a happy camper!!!!!

Ski

Sorry guys, been on a plane, helicopter etc..now at my second home

On the Mahle, the coating was scuffed to allow a profile for the coating to take hold of.
The Arias or Tom C pistons, again, the iron/graphite coating was scuffed to let the PC9 take hold.

Our track car has 100.5mm Tom C pistons in it. We have had the head off due to a valve float. The walls looked great, almost new, as this was after 4 events and break in. Of course we can't see the skirts but the cylinder walls look great. After a total of 10 events all together, the compression is still 147-150, leakdown 2% or less. So far so good. There has only been one little issue with these pistons or I should say rings; one lister got a set and his rings were at the outer edge of new factory spec and he wanted them tighter. I do believe Tom got them to tighten them up because Jim just did an 89 951 in Corpus and the rings were right in the middle of the setting for gap at factory new tolerance. BTW, that car, broke in the same way we did the track car, he's at 2000 miles, compression 149-150 all the way, leakdown 1% or less. This car will see street time and track time.

We know that the pistons from Tom work and do their job, we were just going to experiment a bit more and see how this stuff held up on top of the other base coatings. As stated previously, the other coatings were scuffed to give an attachment profile for additional coatings. The gold coat on Jims 2.8 pistons, actually cures during the first few minutes on running the engine.

J Chen

Hi Ski,
I've always wondered about the side effects if any about
thermal barrier coating on just the piston crown. If the
combustion chamber is left uncoated, would the differential
surface temperature between the piston crown & the combustion
chamber encourage detonation ? Have you thought about coating
the combustion chamber as well ?

Laust Pedersen

Ski, very good information, thanks.

J Chen,
Thermally isolating the combustion chamber will obviously increase the combustion temperature and therefore the detonation sensitivity, but it will also increase the pressure for a 1-2% power gain. The hotter gas will also improve the spool-up of the turbo for a broader boost (and torque) curve. The piston crown coating will reduce (eliminate) oil coking underneath the piston, resulting in cleaner oil (better lubrication = longer life). I would say a net gain if you can tweak the ignition a degree or two, but:

I had my piston crowns, combustion chambers and valve heads thermally coated and had a cylinder wall crack due to partial hydro-lock with port water injection (PWI). My thinking now is that with PWI, I need the component heat to help evaporate the water, which is confirmed on my current car.

So with PWI, I would not use thermal coating in the combustion chamber and without PWI, I would, if the ignition can be retarded 1 or 2 degrees.

Laust

MySwiss

Well I can confirm, after pulling my head off as well, That my Tom C pistons (101mm), which were also coated red, on the squirts and white(thermal) on the dish, they no longer have any coating on the tops(after 3000 track miles).

So I can conclude that the coating is not intended to last more then a few hundred miles..at best.

I obviously don't know about the squirts yet, but I will find out in Mai, when I put a new MID(sleeved) block in there.

AL951

Hey Ski, can you put this coating on any brand of pistons?

Ski

Don't know, that's why we're experimenting with these but I would guess so. Swain has been doing some work for some NASCAR boys too.

Ben Z.

Just for some info, TBCs in turbine engines can provide a 130F drop in temp when only 6 thousands of an inch thick. When combined with internal cooling you can get twice that.

Zero10

Hmm, I'm a little worried about having my pistons coated now...
Is it possible to get all the remaining coating removed, and have the factory coating replaced?

AL951

That is a great question!!.........I am trying to find high copression pistons (9.0:1) for my car, that can work on my stock block. That means that it must have the same coating like the OEMs. Does any one kowns of a good place I could take my custom pistons and have them coated or get them already coated?

BC

Any more news on any of this?

I have a short block that needs to go back together for high temps, and was going to use swain for the skirts and crown.

You guys are saying there are aftermarket options for the Alusil?

Mike S

Just an FYI. I posted a week or so ago a quick pic from my pistons after 5k miles. The coating was still there, although there was a ton of carbon build up on top of the piston. This was with HPC's coating.

https://rennlist.com/forums/944-turbo-and-turbo-s-forum/194390-hpc-piston-coating-5k-mile-report.html

BC

Do you have a Link Mike? Thanks

SoloRacer

What about Cermet coatings? It's used in F1 and the Mazda team used it in their 3 rotor Lemans winning race car. Rotary engines have huge heat issues so I think if a coating was to wear off it would be on them. There is a company in Canada http://www.jhbperformance.com/ that is currently Cermet coating rotors and housings for the RX7 guys. Maybe they will coat pistons as well for a test.

User 41221

ANyone want to post how much the various coatings are costing? I am interested in doing this to a engine I am building up right now.

Regards,