coated headers

[rcodecj]

What's everyone's thoughts on coated headers?
I know they help under hood heat and resist corrosion but...

any horsepower gains?

[Qikbbstang]

JMHO:
Like a lot things in an engine stuff happens so fast it's pretty hard to comprehend. The typical "claim" is the coating reduces heat loss through the tubing and the headers work more efficiently due to the volume of gas flow at a high temp.(obviously the actual mass of gases remains constant regardless of temp FWIW). There is also the claim less heat is released under the hood and finds it's way into the carb.  At 6,000rpm each cylinder is exhausting 50 times a second (if Jack Daniel's and my maths's correct?) . How much heat each pulse actually can dissipate in the hundredths of the seconds it resides within the tubing  between coated and un-coated  I'll leave to you to figure.    Ditto on the old Alum vs Iron Head argument and the time to have a thermal difference in the chamber surface temp per stroke. Let's not forget the alum in a head is usually 3/4" inch thick while the iron head is 5/16"ths and of course the surface area in the iron head in contact with coolant is obviously greater. "   
   Having done my own coating I know few coating shops apply their coating inside and outside the header tubes. Smokey Yunick wrote he found a loss of power when rust/pitting was present in the header tubes.  I'd say it's safe to say there's more power to be had by going with well built headers that use merge collectors and state of the art design then will ever be found in coating.

[My427stang]

I think you are unlikely to see a dyno increase on the slight increase in heat retained in the primaries.

However, before I coated my 6114s, I had a HELL of a time keeping underhood heat in check, which means poor mixture control, potential fuel boiling etc.

I fixed it with a combination of a Boss 9 scoop and coated headers, both made a difference, although you'd think the scoop was the primary, the change in heat at my feet in the car was dramatic, especially on the pass side so I give credit to both

So, horsepower  IN a car that can't control fuel mixture sitting on the side of the road or running poorly on the strip ... compared to one that stays cool and can hold a tune, could be HUNDREDs of horsepower. 

So there are certainly benefits, matter of fact, I don't think I'd build a unibody vehicle or any other tight underhood vehicle without coated headers.    I might cheat in a truck with a lot of room for airflow, but even then, you can see them easier, and coated looks so much prettier

[jayb]

Coated vs. uncoated would be an interesting dyno test, because some fairly respected engine builders (David Vizard comes to mind) claim that there is a significant power increase available from coating headers.  I have some dyno testing coming up, and was considering coating a set of Hooker adjustable race headers for the engine.  Maybe I'll do a before and after...

[fe66comet]

I also wondered about stainless  VS steel. I would imagine chrome would might have some thermal differences also. For while back in the eighties some racers were using header wrap but is seemed to be a short lived craze and I never really heard of any documented gains, kinda smoke and mirror stuff is all.

[machoneman]

Would be an interesting test. Have coated Hookers on my SBF '70 Mach and would always get coated in the future....the  reduction in under hood heat is truly amazing.

Yet...

-most headers get coated inside and out. Does the slickness of the coating on the inside improve gas flow, hence more hp or....

-is it the capture of heat and the expelling of said heat more efficiently the cause of an expected hp rise or.....

-maybe it's a combination of both? 

Don't know how some of these variables could be tested but.....   

[fastback 427]

I have the 2 1/8" hedman headers on my stang. Bought them new, then installed them, had to massage them a little, then sent them off to jet hot. Got them back and they were beautiful. After a year they were peeling and rusted. Sent them back and they warrantied them. Now they are as bad as before. No coating on the inside at all, especially around the collector. I'm not sure if I did something wrong with break in but I wasn't happy with my results.

[machoneman]

Yeah, the process of application is a big deal as I 've heard the same (peeling, etc.).

Mine though were, it looks like, Jet-Hot (tm) coated, the engine had already been well broken-in (i.e. no excess heat due to a new engine) and now years later they look.......just like the day I installed them! 

[fe66comet]

I have run headers on a lot of daily drivers and they all cook up after a while. I also like in IL. Where salt is used so exhaust does not last long, unless stainless steel is used. Steel inherently becomes brittle and degrades with heat so eventually even it the outer coating holds up the substrate degrades anyhow. If you drive occasionally and park it inside they will last a while, if you drive it a lot and go through repeated heat cycles the metal fatigue accelerates the process. Bottom line is if you use it a lot buy stainless and do not worry about HP. If you are going to use it for a cruiser go for the coating and buy a header based on your required parameters like primary tube size, collector size, length and coating. On our tow trucks I run coated headers but still they do not last long regardless, heat and corrosion eats it up.

[plovett]

I don't think I'll put together another hotrod without coated headers.  It's money well spent, in my opinion.

As for horsepower gains, I would guess you wouldn't see much on the dyno.  Those are mostly controlled conditions, especially compared to real world conditions.  On the dyno you can control the water temp and there is lots of air space around the engine, and it's being evacuated. 

In an engine bay, especially a tight FE engine bay,  anything you can do to keep heat out is a plus.  Not just for keeping the motor cool, but to keep the intake charge cool.  A large horsepower difference can be seen there.  If you have outside air ducted into your induction then it'll be a lesser difference, but still there.

So I say yes, they can make more hp.  When you include their other benefits, it's a win-win situation for a modest cost.

JMO,

paulie

[65er]

I have run headers on a lot of daily drivers and they all cook up after a while. I also like in IL. Where salt is used so exhaust does not last long, unless stainless steel is used. Steel inherently becomes brittle and degrades with heat so eventually even it the outer coating holds up the substrate degrades anyhow. If you drive occasionally and park it inside they will last a while, if you drive it a lot and go through repeated heat cycles the metal fatigue accelerates the process. Bottom line is if you use it a lot buy stainless and do not worry about HP. If you are going to use it for a cruiser go for the coating and buy a header based on your required parameters like primary tube size, collector size, length and coating. On our tow trucks I run coated headers but still they do not last long regardless, heat and corrosion eats it up.

It's all relative I suppose, but how long would you say is "a while"?  I'm in a completely different environment  but what I've seen after over two years on my daily driver is that my rust-oleum painted headers stayed nearly perfect up inside the engine compartment where they stay dry.  Down under the car where they get splashed and stuff they were looking a little nasty but it was just surface rust.  No pitting or anything going on.  I'm sure some can get eaten from the inside out and it may vary a lot depending on the fuel used, tuneup, how the vehicle is used etc but from what I'm seeing in my particular scenario is that these headers would probably last through 20 or more years.

 I'm going to change out my headers for performance reasons though, and I think I will go for the coating both for underhood temperature control and appearance.  The barbecue grill paint has worked well for what it is but I'd still like that upgrade.

[fe66comet]

I believe it is the load I haul that kills them, plus the corrosion from the salt on the road. We do not ull a trailer much in the winter but the remaining salt on the road surface stays for months. Also stop and go traffic seems to take a huge toll on exhaust not having much air flow to keep things cool heats things up pretty hot.

[Qikbbstang]

Since Jay mentioned comparing coated to uncoated headers for power production,  I'm requesting if perhaps Jay could try to determine coated vs un-coated in heating the surroundings.  How could someone accurately measure the differences in heat being produced from the header tubing? I don't have a clue if a coated header surface could run at a cooler temp then an un-coated header surface all else remaining the same on the engine. Or is it just a reduction in the amount of heat radiating from the coated  tubing  vs  heat radiating from the uncoated tubing?....How you'd ever measure that sort of stuff??
 

[65er]

....How you'd ever measure that sort of stuff??

Best thing would be to install it and go beat the snot out of it either against the clock or against other cars.  Change something like a header coating or whatever and see how that plays out at the track.   The whole point of dyno stuff is to predict what it will be able to do on a racetrack isn't it?

[fe66comet]

There are two factors that would help the efficiency of a header by keeping the tube cooler, one we already are all aware of and that is dense air is more efficient and shrinks in volume. The other is heat migrates to cool so the heated combustion air will inherently travel to a cooler spot, if the exhaust temperature is reduced scavenging is increased. Taking that into account the amount a coated header would increase HP I would state in a percentage considering what the addition a set of headers added to the overall picture plus the additional scavenging effect. The other factor would be the additional heat removed from the engine compartment in BTU, that would inadvertently affect the incoming air charge and stress on the engine in thermal efficiency. To measure all the factors involved would really work on a car by car basis with factors like engine compartment ventilation and exhaust efficiency taken into account with no changes.