Yet another question about aluminum heads

[El Campo]

So I have aluminum heads on my BB. They always are dirty and clear coat does not hang onto heads from my experience. My question is this: If I have about 11:1 compression is a ceramic coating on the outside of the head going to cause me to have detonation? If I understand it correctly the reason that you can have higher compression with aluminum heads is because of its ability to shed heat. OR is the vast majority of this lost to the water circulating?

[dbmx66]

i might not be understanding what your saying, i may be wrong here, but i dont think its ability to shed heat or water circulation have anything to do with compression. in my book gaining compression is either putting dome pistons in or switch to a smaller chambered head. were you looking at getting the whole head ceramic coated, or just the outside that you see when installed on engine?

[El Campo]

If I understand it correctly the reason that you can have higher compression on an aluminum headed engine is because of its ability to shed heat faster than iron heads therefore staving off detonation even with slightly higher compression. I have 11:1 compression so I do not want to retain any more heat that will cause the motor to be more prone to detonation. Do aluminum heads shed a lot of this heat through radiation rather than through conduction to the cooling system? Like am I going to have detonation because I coat the outside of the head with some sort of coating (so the heads do not always look like crap like they do if they are uncoated)?

[dbmx66]

an aluminum head head cools better then an iron head yes, but you wont see a difference in compression, unless the aluminum head has smaller chambers. i thinking if you coated them it wouldnt make a difference in compression. now would there be a difference in heat, maybe. looking a painted header compared to a ceramic coated header. same difference i would think. but if im hearing you correctly your worried about the heat being "trapped" in the head? i personally dont think there will be a difference, maybe a few degrees at most, but thats it.

if your worried about the heat. id say to put a water bypass on your intake manifold. that help keep the heads cooler as well.

[El Campo]

You are exactly correct. I am worried about heat being trapped inside the head that would otherwise be shed radiantly.
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[Marv D]

Yes ceramic coating would trap the heat inside the material beng coated. That's it primary purpose. I really think your a little off the point a bit in your worry anyways. But first let me say,,, I would not even CONSIDER coating a set of aluminum heads.
From one of the big industrial ceramic coating companies:

"Ceramics require a high temperature to cure the coat (750F); powders require a low temperature to cure (375F)"

I'm not going to take a set of $3000 aluminum castings and put them through that temp,, Even if it were done at casting point while the material was near molten and tolerant of that temp,,,, You WILL warp the heads, and EVERY machined surface would have to be re-machined, valve seats, bronze valve guides everything removed. If you started with a set of blank castings, coated and baked them, THEN finish machined the heads,,, it 'might' work,, or you might have a couple of shiny door stops.

A can of spray carb cleaner and a roll of paper towels will clean your aluminum heads in a heartbeat. MUCH easier of the budget too.

Secondly, HEAT IS POWER. Swains coatings had a real good page on piston coating and the theories behind it, but I can't find it now for some reason. But generally the thought was ..... Put two chunks of material on a hot plate. One a chunk of cast iron, the other aluminum. The iron will not absorb the heat nearly as quickly as the aluminum. And, the aluminum will not retain the heat as long as the iron counterpart,,, right. In the combustion chamber you have somewhat the same scenario. The iron chamber will reflect the heat right back into the chamber, MORE than the aluminum. Heat absorbed from the combustion, allows the aluminum chamber to run higher cylinder pressures and higher temperatures that would otherwise cause the fuel to detonate.

In a race motor you coat pistons to reflect heat back into the chamber, run a fuel that tolerates the conditions, and make more power. A aluminum head street motor theoritically is less powerfull than a iron head counterpart,, IF the heads were created equal (which they are not but another discussion all together). But the cylinder pressures and temps are not so insain that temp issues apply I would not think.

In the end,, what I'm getting at is retaining the heat in the aluminum head is probably not an issue on a street motor. But getting the coating ON the head.... will be

[ll____b0t____ll]

Or for that matter lets say it didnt harm the heads , Which it clearly would but lets say it didnt and you coated them and shortly there after they started peeling or chipping or got scratched?
Now what looks more rinkydink? the original head or the one you made it look like custom crap coating?

[El Campo]

I agree that nothing looks better than bare aluminum. Things are MUCH different down on the Gulf Coast than they are in the west though. Heck, it makes me cringe every time I see guys putting grade 8 bolts anywhere on these trucks without coating them because even inside my concrete floored shop those gold colored bolts will rust. When u have 100% humidity as often as we do, it would blow your mind what happens to bare metals. I'm thinking what I'll do is bare heads and just try to keep ahead of oxidation etc.
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[CNC-C10]

The company that I buy all of my powder coat powder from has a separate division that deals exclusively with Ceramic coatings..room temp ceramic coatings
When they first were perfecting them I was machining a turbo pop off valve for a company. I sprayed the piston and they put in on their test car and it lasted a lot longer without scarring. Were were able to tighten up the clearance and it worked a lot better.
I always thought that would work great for just the purpose you are talking about..keeping alum clean.

http://www.cerakotehightemp.com/
Gary

[ulakovic22]

Clear powdercoat..... I've never run it, but I know a couple people who have. What I don't know about is if it will eventually turn yellow or milky due to the heat.

[Super73]

It was either, Hot Rod, Car Craft or GM High Tech Performance that ran an article 3-4 years testing the detonation properties and HP changes from Alum to Iron. If memory serves, they reported that material had much less of an impact than they originally thought. Reduction in detonation was more about chamber design than anything else. Power was thought to be a combinasion of port design and chamber design.

Do I believe everything I read in magazines? Absolutely not. But I did find it interesting. Things I think the article could have covered (but it would have become a book, not an article) are, same test, does stroke have an effect, what about quench, piston design.. There really are soooo many other variables.
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[GASoline71]

All you really gain from aluminum heads is reduced weight... less weight... go faster...

There are lots of iron heads that flow just as good or outflow aluminum heads.

Oh... and Ally heads look Too Kool for Skool...

Gary

[Marv D]

Now Gary you have to add one more thing,,,,,, REPAIRABILITY. I just injested a squirter screw into the zero decked motor on the track and it beat things up pretty seriously. A little welding, milling, some valves and seats.... and they are just like new.

[GASoline71]

Very, very true Marv!

Gary