Ceramic coating vs. Polishing

[brysonc]

I know the effeciveness of ceramic coating is kind of a controversial issue, but I was wondering what you guys thought. I understand how polishing helps by minimizing surface area, but does it really "reflect" heat? What are the advantages of each in the combustion chamber of the head and the piston crown in a 4 stroke turbocharged engine? How about in a N/A engine?

 

[ivymike]

diesel or gasoline? I know that polishing the piston top can have a measurable effect (reduction) on piston temperatures in a diesel, but it only lasts until the soot&carbon layer builds up. It works by reflecting radiated heat, as you suggest.

 

[brysonc]

Sorry I wasn't more specific -- it's a gasoline application. I coated the pistons, combustion chambers, and valve faces in my previous engine, but really have nothing to measure it against. I'm about to build a new engine and am trying to decide what to do.

 

[fastmax]

Polishing CC's or pistons is going to provide short term benefits at best --- as mentioned it only takes a few miles to build up a coating that would obscure your polishing job.

Why the adversion to coatings --- I was of the impression they were effective if properly done [ Swain seems to be a respected outfit].

Is your concern piston temps ??? Oil squirters can reduce crown temps but may be a pain to install if not offered in a stock block.

Jim

 

[Majik]

We've seen the coatings properly applied help definitly in a turbo gas setup. Thats where it provides the greatest benefit. If it's a street car 9.5:1 I would say the effects are minimal but if it's a high CR gas racer then I would definitly do it. I also apply the coatings so I'm not faced with the huge bill of getting it done.

 

[brysonc]

I apply the coatings as well -- we buy coatings from a company called techline. I have a link to a thread where someone heated up the faces of three pistons, coated, uncoated, and polished with a torch from an inch away for a given amount of time. It's a poor experiment, and not exact by any means, but he said that both the coated and uncoated pistons gained 135*F, while the polished piston gained 91*F.

http://www.ls1tech.com/forums/showthread.php?t=435566

There's the link. In what ways could his experiment not represent actual combustion chamber effects? He mentions radiant vs. conductive heat, but I don't know what to think. What do you guys think about it?

 

[fastmax]

I've used the Techline on my current setup, external components only, headers, downpipe etc --- The car is a twin turbo Mitsu 3000gt. Fairly cheap and easy to apply, however, it did burn off of the turbine housings --- maybe an application problem, improper prep for example. Or maybe it just won't hold up the the heat generated by the turbos on a road track --- WOT for up to 30 seconds.

I was under the impression that the big boys used plasma deposition or some such application process not available to the home user.

Jim

 

[patprimmer]

Techline's Ceramacrome will take turbine housing temperatures if applied correctly. It will go dull, but will leave an insulating coating.

Ceramic coatings are very thin and only offer a minimal thermal barrier because of that.

Meaningful tests would need to measure rates of heat transfer, not surface temperature changes, as a good insulator will actually get hotter on it's surface, but stay cooler in it's matrix if it is exposed to a heat source for a short time.

Applying a gas torch flame sounds like a very unrepeatable test to me.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[brysonc]

He had a thermocouple mounted on the underside of the piston, but I agree that the test wasn't carried out well. Would polishing provide more of a benefit than a thin layer of ceramic coating, or do you guys think ceramic coating is still the best option?

 

[DDRSS10]

I had a two stroke gasoline engines piston crowns and heads coated by swain. It is a ragged edge set up that I had problems with burnt pistons in the past. Some pistons only lasted 12-16 hrs. I have reduced the oil consumption by 35% leaned the motor out by 5 jet sizes(about 12%) and the pistons have held up for 120+ hrs now. It is something that a would recommend to anyone, although for a safer setup the benefits would probably be less. My motor spends 2-3 min. at wot and nearly full load, if the coatings have made as much difference as it has for me I can't see why if you could afford it you wouldn't use it.

Nick



"Speed costs money boys, how fast do you want to go?"

 

[brysonc]

Hrm...I wonder how different the Swain coatings are from the Techline stuff I use. I know that they are applied much thicker, but it can't be a *whole* lot thicker before it starts affecting combustion area and quench and stuff.

 

[Majik]

Swaintech I believe is plasmasprayed on there. After talking to lenord of techline he was telling me about how the coefficent of thermal expansion on their coating will not tolerate pistons with a high ammount of expansion and it will crack and begin to flake off. Could be sales talk but Lenord has been a straight shooter in the past.

 

[fastmax]

Yeah, there's an interesting caviat here --- any coating on an internal engin part --- piston, valves inside headers etc. --- better stay on the part in a turbocharged application. Small flakes of misc. trash hittint a turbine impeller can do some significant damage when the turbine is spinning at 100K+ rpm. it doesn't take much erosion to unbalance an impeller.

Jim