924Board.org

[Fast924Turbo]

Agreed Vaughan. Hell, you don't even have to go to Rennlist or a Porsche or GM maker to see the effects of coatings on pistons. NASCAR?

I got teflon on my skirts, and thermal coatings on the crowns of my pistons, from, you guessed it, a high performance motorcycle engine rebuilding shop.



PS: They do high performance 2 strokes too - so they know the forces on engines just a little bit.

[Peter]

Fast924Turbo,
I don't have Corky's book in front of me so that I can quote him directly, but I will try and explain my understanding of it.
Piston coatings on the top are designed to reflect the heat of combustion back up into the combustion chamber, which will help result in more power. Not a whole lot of power, but every bit helps. I am sure we can all agree so far. Without coatings, the pistons absorb some of the heat. Just like every other part of the engine will absorb heat; such as the head, valves, & valve seats (which are specifically designed to take some of the heat from the valves and disperse it into the head). Corky says that if the engine as a whole can take more heat, which is what you are doing with a piston coating, then you should just turn up the boost. Remember that if the piston is not absorbing the extra heat it was designed to, rather directing it into the head, valves, valve seats, then the engine as a whole can take more boost and you don't need coatings. Makes sense to you?
Once again this is his opinion. I personally think that any benefit comes from coating the entire engine: heat coating the piston tops, head, valves, exhaust ports, exhaust manifold, etc, to keep the heat within. Costly! Lets not forget teflon coating the piston skirts, connecting rods, and counterweights of the crank to shed oil and thus reduce weight on rotating/reciprocating components. Costly! And now you have just a few more horses. For my application, I can't justify the costs. To each his own.
Just a side note: through my research on piston and engine coatings, I have yet to find any dyno charts by the companies who sell these products or the racers who use these products as to the HP benefit of engine coatings. Seems strange to me.
Initially I thought about a three-system coating for my 931 pistons: tops get heat reflective coating, sides and underneath get teflon coating. However the costs involved and the Porsche people who I spoke to stated that piston coatings do not yield any significant reward. Thus I did not use coatings. To each his own

Vaughan,
I understand about the "this is how it has always been done" mentality. Now, if I could do my own study on coatings, then I would not rely on others experiences/opinions. However, because I can't, I have to rely on people I trust & respect. If my local Porsche race engine builder doesn't use coatings, & I respect their opinion, then I too will not use coatings. It is as simple as that. If the people you trust & respect use product A, you will use product A.
As for Saturn or GM using coatings or other new technologies, I don't doubt your statements. But unless you are privy to internal Saturn memorandum, you can't tell me why they are doing what they are. I can speculate that maybe a teflon piston coating will allow the engine to use thinner oil and thereby increase fuel economy. Increasing fuel economy will allow the company to meet new Federal Laws, thus allowing the company to stay in business. This sounds plausible to me.
As for your GM friend saying to use them, my Porsche friends say not to use them. Woodcote Racing, the shop that repairs the 924GTP that I posted a pic of in a previous post says not to bother. They also repair various factory Porsche racecars, not just 911s. A local NY Porsche race shop (forgot their name but Vince P. was with me when I spoke to the owner) says they do not use them. I don't want to start a pissing contest, but the only thing I can say about GM & other US car manufacturers (from having owned their products) is that the cars are cheap & the parts are available everywhere. As for quality: Ford Pinto --BOOM! --death! US SUVs--ROLL OVER -death! I am sure you are aware that US cars rank below European, Swedish & Japanese cars in quality & performance, so I won't do a Porsche to GM comparison. No flame intended.
As far as I know Porsche, specifically Mahle, does not use special coatings. Please correct me if things have changed. I searched through Bruce Andersons 911 performance handbook and there is no evidence of special piston coatings, either on production or on racecars. The only thing that comes close to teflon like coatings are the Nikasil lined cylinders that Porsche uses. Bruce says they allow a smaller piston to cylinder gap which causes a slight increase in power. I guess that using a teflon coating as Saturn does is cheaper than running Nikasil cylinders as Porsche does. But the quality is not the same.
My oven has a ceramic coating. What does this mean? NASA uses special coatings on the space shuttle, but they also use real gold for their electrical connectors.
As for people on Rennlist using them, many people do. Rennlist is just another list. There are people on this list that make HP statements about engine mods without any dyno charts to back it up. Everyone is entitled to his or her opinion. But when we don't have first hand experience, we rely on opinions of people we trust & respect. I trusted the opinions of the Porsche people who told me not to bother. I am not trying to flame anyone, like I said earlier: some people swear by these coatings & others don't. Whatever makes you feel good.

[Fast924Turbo]

Peter,

Thanks for the good reply. It makes sense.

I don't have Corky Bells book. So I can't use the same authority. But the way you've described his explanation for coatings fits with (a) my understanding of how it works and (b) other authorities in books, friends, internet and of course here.

I suppose the smartest thing, given this information, and given what I've already done to the pistons, would have been to go 3 more yards and spent some more money coating the intricates around the head. I still have some time to do so and might still do it on this second engine I'm building up.

I tend to work much the same way you do too. I get the best opinions from everyone who is knowledgeable, and I sift through and select out what is best given my own understanding. I'm prejudiced: I want reliability under stress. That's my bias. To me, hearing something doesn't work very well is a much less damning critique than hearing it will harm my system. But if they say something might be damaging for my system or my finances, I'll weigh that advice really seriously, regardless of reputation. To date, I haven't heard much from the authorities I respect telling me that these coatings will harm my system, so I'm ok with it so far. What I'm a little more sensitive to now that you drive it home, is that in deflecting the heat from the pistons, it could be possible that I just might be adding heat elsewhere. I'm going to look into that possibility.

The purpose of my using coatings isn't necessarily HP improvement, although I'll take it if that comes, instead, it is just to protect my system a little bit and allow me to build up the system later if I chose to do it.
_________________
Most men, when they think they are thinking, are merely rearranging their prejudices.
Knute Rockne (1888 - 1931) US football coach