I originally planned on coating my piston crowns, combustion chambers and valve faces with Swain's Gold ceramic coating. After reading Maximum Boost by Corky Bell I am questioning this option.
He talks alot about detonation and thinks that these ceramic coatings just add to the possiblity of detonating under boost because they keep heat out of pistons(which I agree is good) but make it stay in the combustion chamber, making temps greater, and closer to detonating.

Who agree's with this and who doesn't? I am thinking that I will be fine with a good intercooler to keep intake temps down, but I don't wanna make a mistake.
Any suggestions or experiences will help.

Hunter

 

Detonation and preignition are differerent phenomenon, but are closely related. Preignition is defined as the ignition of the fuel-air mixture before the regular ignition spark from the spark plug. Detonation occurs when excessive heat and pressure in the combustion chamber cause the air/fuel mixture to autoignite. This produces multiple flame fronts within the combustion chamber. Both can lead to engine damage. By coating the piston crown and valve faces, these surfaces are kept cooler and more heat stays in the combustion chamber during combustion. This heat is what drives the piston downward, that's why thermal barrier coatings can produce more power.

But this extra heat is all within the combustion gasses, and when the exhaust vlave opens nearly all of it exits into the exhaust port and out into the headers. When the fresh intake charge is introduced, it doesn't "see" any of this heat. In fact, since the intake valve is cooler, the intake charge temp is lowered and it picks up less heat from the other surfaces as well.

So, I disagree and think that coatings are a good idea. So good that I use them.

Rich Krause

 

My engine has no coatings on the piston tops, and that sounds pretty much like the reason I was given for not coating them in an engine with a huge dose of nitrous. I wasn't able to discuss in detail, because at that particular time in my life I was working in Italy and my engine was being assembled in PA, and communications were "limited".

They did propose an alternative to a ceramic coating, but they swore me to secrecy before they told me what they recommended.... but it was not a coating.

I really feel ignorant in this area, because if you listen to Swain or Ray Bohacz on coatings, there seems to be absolutely nothing negative about them.

 

And the other thing is that the aluminum alloys used in pistons melt at something like 1300-1400F. It's nice when you don't exceed this temp! Actually, though it's been a long time since I studied materials, I think you don't even want to get too close to the melting point of metals under as much stress as pistons. They start to deform and bad things will happen.

I'd be very interested to know of any real downside to ceramic coatings.

Rich Krause

 

why stop there? why not coat the piston walls and entire combustion chambers?

Is it because the ceramic coating is too soft for the walls? what about the combustion chambers?

I would be correct in saying that the less heat is lost out of the "bore", the less power is lost/most is made?

 

Ya I thought I was correct in my thinking that ceramic coatings on the pistons would help reduce detonation. I talked to Swain coatings for at least 35 mintues about this and I am convinced that they are good. Maybe not in nitrous applications, but in forced applications I think its a good option.
And yes I dont wanna melt my expensive JE pistons, or get they anywhere close....that would not be good.

Coating the walls...I think it would casue to much friction, and they would be scraped off. Combustions chambers would be coated, this is good to keep the heat in too.

But Injuneer, I would like to hear your engine builders reasoning for not using coatings in a nitrous engine. I wont be using nitrous but it would be interesting to see why they decided against this.

Hunter

 

I had my engine coated also - pistons, skirts, bearings, combustions chambers, and valves.

Everything else aside, the more heat energy you keep "trapped" in the gasses in the chamber the more torque you are going to make.

As Rich pointed out, I don't see any way that these coatings are going to lead to any detonation or pre-ignition conditions - if anything they should help either.

From my perspective the only real downside is expense - I tend to think they will/should be - but that depends on your priorities.


Chris

 

This might not be applicable as it comes from the turbine engine business but here goes anyway. The one short-coming with ceramic coatings is what happens when the coated part is rapidly heated and cooled. The metal expands and contracts much more than the ceramic. No matter how good the bond between the two there is the possibility of it breaking down and having the ceramic flake off. Maybe with a nitrous motor the massive pulse of nitrous and fuel could be doing too much cooling for the ceramic/aluminum bond to perform properly. Maybe?

 

Mahle claims their coated pistons are worth 10-15hp over other pistons:

“All pistons are surface treated with phosphate coating that aids in the break-in of pistons and pin. Grafal® surface coating treatment is applied as part of the machining process. Grafal®, a thin layer of small resin particles, reduces friction and provides increased lubrication allowing our components to withstand harsher engine conditions while reducing detonation. Bottom line:
Less Friction = More Horsepower.”

“MAHLE Racing pistons use a low tension ultra thin ring stack (1.1mm, 1.1mm, 3mm/.043", 043", 3mm) to reduce friction while still maintaining proper heat transfer. The ultra thin ring stack results in reduced friction and extra horsepower.”

“MAHLE is on the forefront of piston materials research. They have created the M124-S and MSP25-S alloys specifically to make lighter weight components with the strength and stability to withstand extreme pressures of racing. SB Chevy and 351W weights starting at 367 grams for the 4BBL class and even lighter in the 2BBL class!”


Now my question is….? Who believes this and is it the light weight, coating, thin rings or “all of the above”???

I frankly find it very hard to believe unless your spinning a motor to 9K or something.

 

I belive that the anti-friction coating on pistons skirts (which I plan to use) is a good idea. Reducing friction free's up horse power not matter what. Only some techniques may come into play at high rpms, but skirt coatings and reduced tension rings will free up horse power below 7000 rpms, I have seen dyno after dyno tests that show this.
Now the differences maybe 2 or 3 hp at 6500 rpms on a N/A motor, its much different on a FI motor. As loads go up, so do the frictional losses, so difference of 10 to even 20 hp maybe seen with coatings and low tension rings.
Now I am not saying that all motors should have skirt coatings and low tensions....that would be stupid. Unless you have a dedicaed drag racer low tension rings are out of the question to me because of more oil consumption. But if you are a racer, then its worth that extra oil for 10 hp.
Obviously lighter components reduces the power needed to accelerate them, so this will 'free up' horsepower, but I am not sure how much. It would be a pain in the *** to have to do dyno testing on this weight stuff, but in theory it seems right.

Bottom line, skirt coatings are worth it to me on my engine while I am still undecided about the thermal coating.
I am going to talk to Swain a bit more about the evenness of their applications, as I can see how unevenness can cause hot spots.
If anyone has any more information about using thermal coatings please share.

Hunter

 

hmmm- ok- stupid question time
isn't the same coating we see on headers right?

should i bother coating my combustion chambers and valves while i am putting it all together?

where do i get this done?
how much?
worth it?

 

I've looked into coatings alot.

First to answer Denny McLain,

The Mahle pistons are all about reducing friction and yes it's all of those things, the friction coating and the narrow rings. That's basically what a winning engine is, not one magical thing like a cam or 5cfm more flow, it's a bunch of little things that add up. The lower weight is going to help crank life and the high rpm/sec acceration and the additonal HP that it allows. If you have a Bonneville engine you don't need light parts really. A drag car or circle track car benefits greatly from them. Friction reduction comes in many forms, and coatings along with lower drag rings are some of them. Obviously the higher the RPM the more benefit you get, and on something like roller bearings for the cam, since it only turns at half speed, you need alot of RPM to see everything from them. I'd say that friction coatings are important, not as much as thermal ones. Yes a engine makes XXX amount of HP and loses some of it to friction. There are alot of things to reduce that, it's probably not the first place to go look for HP. I'd always spend the money on the heads first. If you're going to spend $10k on heads then you should probably have coatings. I would buy an electric water pump, underdrive the pulleys and get a electric fan before I put coatings in the engine.

Friction coatings are a different animal from the Thermal coatings.

The basic premise behind thermal coatings is that you marginally improve the thermal efficenentcy of the engine. By marginal I mean .2-.5 of a %. That's not very high, but it does help. The reason being that a engine is very thermally inefficient. Operating in the 35-37% range, where only that amount of the heat produced actually pushes down on the piston. While the other part escapes down the exhaust port. Now a .2-.5% total improvement is actually a .5-1.3% increase in thermal effiecency. So I have .5-1.3% more pushing down on the piston. That means that you can have that much of a TQ gain, and sometimes it's a higher percentage. So at 700 ft lbs we can find about 15 ft lbs, the higher the RPM the more HP you find. On a 450 ft lbs engine you can easily find 10 ft lbs. As I said above winning engines are not just one part but a combination of many little things that add up to that winning edge. Coatings are one of those.

One more benefit is that you can keep the total engine temps down, oil, coolant etc because you keep the heat in the chamber and exhaust. That means thinner weight oil, and lower temps to keep the air/fuel charge more dense and therefore make more power. The longer the engine runs the more they benefit you. Maybe a Pro Stock engine doens't get to much from them, but I would still run them. WJ has actually said that he doesn't like the fact of higher temps and on the edge compression ratios, and on a one trick pony like a Pro Stock engine I kind of see his point. On the other hand I'd rather run the same compression and have the coating help protect the piston and chamber from detonation. It's only got to live 7 sec at WOT so, hopefully it will.

Again, are these good for a street motor. Yes, are they the best use of your money. No. SPEND IT ON THE HEADS! Coatings are a last resort for HP, they are not high on the list. $1000 in coatings can go along way in head work, and 20cfm more (if the cylinder sees it) is worth more than $1000 in coatings.

One more way to look at it. It's about $500 for just TBC, to gain 2% more power that shoudl be about 2% of the engine budget, so at least a $25K engine is what you need to be looking at to realistically do this. Or there better be alot of prize money if you win.

Bret

 

Bret: for a street or street/strip SC or nitrous application the issue of lower piston crown temps eclipses the power gains. The commonest major failure for these applications relate to the pistons. Anything that lowers piston temps (I have heard from Swain that it can be up to 200F) in these motors is a blessing!

That's the reason I use them. Inspecting the crowns after 8,000miles revealed a completely intact coating, BTW. Swain was used. I fully expected to buy new pistons this year, but after close inspection I popped 'em back in (with new rings).

TBC coatings on the crowns are a good thing for a blower app regardless of any power gains, IMHO.

Rich Krause

 

Well its decided, my crowns, combustion chambers, valve faces, exhaust ports, and turbine housings are all being coated with Swain's Gold Thermal Coating.

I am really contimplating whether or not I should coat the headers. Only money will tell....

Hunter

 

Heck, that would have been the first thing I coated. If nothing else to keep them from rusting and looking bad. That is unless they're stainless, but if the extra $200 or so for coating is bothering you then I doubt they are...

IMO skip the exhaust ports and put the money towards coating the headers.