Piston coatings

[Suzukidave]

Guys , what do yall think of the merits of having the piston crown and skirts poly coated ? I have read good feed back on the crown coating but have read that the skirt coating can reduce the pistons abilty to cool itself or is this false and most of the heat goes out on the rings ?

[chainsaw]

here is a little info I found. Dont know if it helps you or not.


Pistons
Most stock replacement pistons for earlier applications are cast aluminum, while late-model engines use hypereutectic designs. Cast pistons should not be used with forced induction since they lack the strength needed to withstand the additional cylinder pressures and the possibility of detonation. OE hypereutectic pistons do not have as much silicon as the aftermarket Keith Black design, and as a result they are brittle and break easily if detonation occurs. They should be replaced with either higher precipitated silicon pistons from Keith Black or forged units.

The need to use a lower compression ratio with forced induction is usually met with the piston crown design. Dished pistons that mimic the shape of the combustion chamber are the current trend. Full-floating pins should be used, and the pin bore should be placed as far down from the crown as possible. Applications that have the pin bore migrate into the oil ring area should be avoided with boost pressures above 10 psi.

Piston coatings, though not new to the motorsports industry, are finally being seen as worthy additions to a forced-induction engine. Swain Tech Coatings apply a ceramic thermal barrier to the crown of a piston to reflect the heat of combustion back into the expansion event while keeping the piston and ring package cooler. The coating not only allows the engine to produce more power, but limits the possibility of detonation and decreases brake-specific fuel consumption. In addition, a dry film lubricant should be applied to the piston skirt to help protect it against scuff from the high temperatures experienced during boost.





here is the site it came from





http://www.300below.com/site/rodsperformance.html

[ja-moo]

A racer told me it "eases" things when you get a seiuzure, so not such an abrupt "stop" of crank rotation......

[CJF]

Guys , what do yall think of the merits of having the piston crown and skirts poly coated ? I have read good feed back on the crown coating but have read that the skirt coating can reduce the pistons abilty to cool itself or is this false and most of the heat goes out on the rings ?

I'm betting it has to help. In fact, I just sent my pistons to Bill Bune for a thermo and moly coating. I have done some research on the topic. Most car racing teams (especially drag racing) coat their engine components. There is some debate on the true value, but general thoughts are that less friction and lower temps are better even if by a small amount.

[derek]

i am getting the piston tops and head combustion areas ceramic coated (as soon as i get the motor torn down that is). not sure if it will net me any gains but i figured it couldnt hurt.

these guys are doing it for me
http://www.rukindustries.com/services.html

[Suzukidave]

Bill Bune does great GT crank work so i would like to send him my pistons also , but i was also looking at Swain Coatings http://www.swaintech.com/

[rbond]

I too think the coatings would be a benefit in the long run as in reducing wear. My only concern is on the Wiseco pistons, the rings are very thin, I would think there would be a little less sealing and less heat transfer to the cylinder. Almost enough to negate the benefits of the coatings. Besides, a stock T/GT500 is such a low compression engine the coatings, strengthened crown, etc. it should make a re-bore wait a lot longer...... It might even run smoother..? Has anyone got a set installed who can tell us how well it runs?

[tz375]

We need top back up a little here and think about what happens in a cylinder. The primary heat transfer is between the rings and the barrel.

The secondary path is through the oil film.

Rings seal best with a nice thick layer of oil (these terms are relative). Heat transfer is worst with just a boundary layer of oil from too little oil supply or no oil!

So more oil makes more power and keeps the motor cooler and therefore cleaner (that info came from an SAE paper not Jennings BTW).

The piston should never touch or rub against the barrel surface. So what is the point of Teflon coating the skirt? The first benefit is reduced friction and we all know that the largest mechanical loss in a motor is in the piston/bore friction so that must be it. Almost but not quite. AFAIK, the friction improvement is almost almost immeasurable and most of the friction is the rings.

The top reason for coating piston skirts is insurance. If the oil film breaks down even for an instant, the piston and barrel could become one, so the teflon provides some insurance against that short term terror.

It can't do much with a full on detonating motor but it does provide some margin before meltdown and that might just be enough time to whip the clutch in and save it.

[Suzsmokeyallan]

Richard i like it when you go back to the oil thing,

So more oil makes more power and keeps the motor cooler and therefore cleaner

In relation to two stroke mixture ratios, we will disagree on that statement forever.

[Suzukidave]

I guess the same holds true for the crown coating that it will provide just a extra edge of burn through protection and its a reasonable price to have each piston coated . Swain Tech coatings

TBC on Dome and Poly Moly on Skirt ……................ $32.00 each
*TBC on Dome and PC-9 on Skirt* ………................. $38.00 each
Gold Coat on Dome and Poly Moly on Skirt .............. $48.00 each
Gold Coat on Dome and PC-9 on Skirt ……............... $52.50 each
Dome Only with TBC ………………………................. $24.50 each
Dome Only with Gold Coat ……..………................... $42.50 each
Skirt Only with Poly Moly …....…………...…............. $14.00 each
Skirt Only with PC-9 ………………….…................…. $18.00 each
Heavy Skit Build up with PC-9 (.002-.004”)…….......... $24.00 each ----------------------------------------------------------------------------------------Bill Bune MOLY COAT (PISTON SKIRT)ea15.00
THERMO BARRIER COAT (PISTON DOME)ea15.00
MOLY & THERMO COAT 25.00

[tz375]

Allan,

I thought you would catch that one.

That's OK. There are many people who are convinced that less oil is best. As my brother would say, "I'm OK with you being wrong about that".

All I can do is to point to the studies that have proven it (as far as I am concerned), but they didn't necessarily test under normal road conditions at part throttle and part load where less oil with higher safety margin might be good enough under most conditions. I think that was your point originally - that less oil is OK on the street with modern oils

There are many opinions, and yours and mine will probably never be aligned, but seriously, wouldn't life be boring if we all agreed about everything.

[rngdng]

The oil issue will never be resolved, but I do have coated pistons in my RD....so far, so good.



Lane

[TLRam1]

As my brother would say, "I'm OK with you being wrong about that".

I will have to remember that one.

[rngdng]

As my brother would say, "I'm OK with you being wrong about that".

I will have to remember that one.

I prefer, "It's your lie, you can tell it any way you want"!



Lane