The thermal coating functions as a piece of insulation, and is applied to the outside only. That allows the metal to absorb heat from the inside at the regular rate, but slows it from radiating that heat on the outside. Because the metal cannot radiate heat on the outside as easily, it accumulates heat and the temperature of the metal rises. As it becomes saturated with heat, it can no longer absorb heat easily from the inside. This is called 'heat rejection'. The more heat it rejects from the exhaust, the less heat the exhaust pulses lose to the metal as they travel to the turbo. Hotter exhaust gas spins the turbine faster, which spools the turbo faster and quickens response time.

One could thermally coat a cast manifold, and some persons do. But since a cast manifold doesn't radiate heat as rapidly as a thin-walled tubular type as it is, it doesn't benefit as much from the thermal coating.

 

This is only true when the manifold has been saturated by sustained full load EGTs, which in practice rarely occurs in turbocharged apps outside of commercial diesel applications.

As for radiation, I'm not sure I understand what you're getting at. Radiation heat transfer is a function of the material's emissivity and surface area, neither of which care of cast vs tubular.

 

Inconel is probably the best commercially available material for a manifold. Very high strength at temp and very low CTE and thermal conductivity. Turbo manifolds at the highest form of motorsports use inconel almost exclusively.

On the flip side, inco is heinously expensive and a royal PITA to work with.

 

wow, good read. keep it going! you're making me smarter!

 

Can't you coat the inside of the material also? With a cast manifold I took a wire wheel and a dremel and ported it out. Well the stock one I should say. I liked the way it felt at low end. Maybe my butt dyno lies but my butt said it was faster lol.

With inconel I already knew how expensive it is. Lol I take 4 barrels of it to a recycling place and get 2 grand out of it just for scrap lol. But can it be coated will it not lose the thermal efficiency and also why is it a PITA?

 

Coating the inside is great in theory, but in practice it's very difficult to get anything worthwhile to adhere and and hold up over the long term. The good stuff (Swain or Zircotec) is a line-of-sight operation, meaning it is sprayed. This makes it impossible to do the inside of a manifold.

Slurry operations, where you dunk the part in a soup of the stuff and then it "sets up" afterwards, would be great but the types of coatings that use this process aren't really thermal barrier coatings.

Coating an inco manifold wouldn't really be worthwhile since inco has ridiculously low conductivity as it is. It just doesn't get as hot on the outside as, say, cast iron would.

Really, thermal barrier coatings on exhaust manifolds are less about performance and more about preventing exhaust heat from cooking other stuff in your engine bay. True TBCs that actually do something (many are just decorative) inherently make the wall temp of your manifold go sky high and compromise the manifold's longterm durability.

My advice is to forget about TBCs on manifolds and just place a heatshield on whatever you want to protect from the manifold's heat. It'll be cheaper and more durable in the end.

 

Oh, and inconel is a PITA to work with because it is hard as hell (lots of nickel), strong as hell, and requires a skilled welder to deal with its particular idiosyncracies--the weld puddle tends to look like it has oil and dirt floating on it and its just not as forgiving to weld as, say, stainless.

 

Yes I like Inconel

And boy does it cost $4500+ just for this manifold but its not for a Evo but it weighs just about nothing.

Mark

 

Mark now that is a manifold. Let me guess, Primary Designs?

 

Yes, IMO they make the best manifolds in the UK.

Mark

 

PD do stunning work. Very nice piece. Is that Zircotec on it?

 

Yes Zircotec on it, Yes PD do awsome work and did the design to how I wanted it with the TS and the results have been outstanding.

Mark

 

Iam sure they do

 

That looks like Jame's drag car

Mark

 

off topic but whats being driven off the cam gears? ^