Header coatings ??

I have been looking into sending my headers off to have them ceramic coated, mostly leaning towards JetHot, but I have some questions maybe some of you pathfinders may have answers to.

On our sons car the previous owner put ceramic coated headers on the car, one collector cracked and a peice broke out, and I have never really seen a failure like this before, it looked as though the metal was very brittle. This has me thinking if the coatings have a downside.

Additionally, the collectors on the 308 have a straight section pipe welded inside a cone peice that comes off the tubes, and it extends an inch or so inside. I assume its not that condusive to exhaust flow. Should I be concerned with this enough to cut it back and smooth it into the cone for improved flow before I send the headers off for coating? I have read the exhaust flows to well already and to leave it alone, so any thoughts here would be helpful.

 

I have no idea on whether or not you should leave the cone piece in or not, but I've had headers and test pipes ceramic/aluminum coated in Jet Hot's "brilliant" finish w/ excellent results. I would use them again.

 

Had my rear header off working on the differential, so I took advantage of the opportunity to send it to Jet-Hot for their satin black coating. Just couldn't convince myself that the chrome headers look was right for a 308. Had them double coat the inside. Just got it back this week. Sure looks nice. Will be a few weeks before I get the car on the road & can assess results.

The header was starting to show it's age, & some rust, so decided it was time for proactive steps. It's mild steel (a Euro header). The tubes blended in pretty well where they came into the conical combiner, so I didn't grind them down. However, more dramatic protrusions are probaly worth removing.

BTW, in addition to Jet-Hot, Kermit's company: www.durable1.com offers a ceramic coating service, along with rework like you're talking about. Kermit's very familiar with 308s. Almost went with him, it came down to a coin-toss & lower shipping costs from NE won out.

If I were having rework done like you're talking about, I'd have probably gone the other way as he knows 308s. See the pix on his web site.

 

FWIW,

The otto cycle engine is an ill conceived air pump.

ANY thing you can do to improve the intake or exhaust flow will produce more output, (HP).

There are a lot of "losses", friction, pumping, auxiliary load and heat loss, It is our great loss that not all of the gasolines energy can go into propelling our beloved toy foreward.

So, anything that you can do to reduce those losses will translate into greater left over power to make it go.

A few simple things come to mind:

less restrictive exhaust, (not as much power required to pump out the spent gasses.

Less restriction on the intake side, high flow air filters, removing sound deadening junk in the air filter housing, (thanks Spasso). We probably cannot have more than one choke per cylinder, so more carburetors are probably out.

Lower friction oils, blueprinting the engine, narrower compression rings, chromed cylinder bores, better balancing of the engine parts.

Reduction of thermal losses by insulating or coating the exhaust and more esoteric stuff like ceramic coating of pistons.

Optimizing fuel injection, ignition timing, cams, port and valve sizes and compression ratio are way beyond me at this point.

hth,
chris

 

Paul
Here's what I understand:
- the US headers are offset versus the exhaust ports. 5 BHP gain from alignment. Tested by Casey @ Carobu. Not present on Euro and comp.
- Jet Hot assists scavenging and will tend to lean the mixture slightly as a result. People I have talked to (race techs) are very positive about the ceramic coatings.
- On my 77, I do not have the protrusion you are referring to. Smooth. I am sure it would be advantageous to smooth out. (Generally, you want to do all you can to limit reversion of the ex gas back into the head).
HTH
Philip

(P.S., The issue with the ex ports (valves) is that they were too large for optimal tuning)

 

Anyone use the following coating service? They look very good:

http://www.swaintech.com/header.html

 

Ceramic coatings are very beneficial for headers. The benefits are three-fold. 1. The coatings reduce heat transfer from the exhaust leaving energy in the exhaust gases in helping them exhaust efficiently. 2. The reduced heat transfer results in lower underhood temps that reduce temp of intake air ( more power) and also protects under hood components from heat damage. 3. The coatings also help preserve the header material. It is important that you coat the inside of the header as well. The coating on the inside minimizes heat transfer to the base metal - helping the longevity. Only coating the outside can accelerate the deterioration of the header since heat can be transfered from the gas into the metal, but the heat transfer to the outside is reduced due to the coating, resulting in higher temps in the metal. 4. The header appearance is improved. There are many different colors available - you are not stuck with the "chrome look".

Ok, so they're four-fold.

I recommend using HPC ( www.hpcoatings.com )

Vince

 

Vince hit a very important point in his reply.
Most US 308 headers tha I have seen are constructed out of mild steel flanges, welded to Stainless tubes.
That is where the problem can appear. By the nature of the metal, SS moves around much more than other metals when exposed to thermal changes . By only coating the outside, or not properly cleaning the inside before application, you end up with the ceramic actually trapping MORE heat and the resultant expansion which is a major cause of cracks. This is kown to cause problems, Ask the MFG how they process. The companies mentoned earlier are of high quality from what I hear, and I would not be the slightest bit leary of their work. If the company claims to sandblast around corners, I would walk away.
In my experiences, the US model headers have some problems, such as port misalignment. This can easily be checked with an old gasket, by holding it up as if the header were installed. Remember to allow for drop due to gravity. I've seen 3/32" misalignment frequently.
The tube that protrudes into the collector flange MUST go!
I use a torch, and with the header careefully clamped down, heat the inside part, and use a piece of pipe to "fold" it, or bend it over. What it is doing for the header is a reverse version of "Step Pipes" used in other forms of racing By going to succedingly larger tubes, this square end causes a barrier of sorts for reversion. The exhaust on this system will easily transition into an open area, and the zone around the "step" is really quite dormant, somewhat like a slow waterfall, with not much turbulance. Turn this system around, and it hits the tube end, causing a lot of turbulance (this hopefully helps explain the succesfull use in aiding reversion problems by the use of step pipes.)
Whoever you decide to go with, make sure it is a reputable company. Ask around. there are many colors to chose from .enjoy You will be amazed how much the temp level under hood drops!
The usual disclaimer, no sales promoted, simply the exchange of information for the good of all.
BTW: Old Pruning shears make quick work out of the old aluminum covers! I wouldsuggest that you moisten the insulation first however, just to be safe.
And lighter to ship, as they do add up!
HTH.
Kermit

 

Jet Hot is a pretty amazing thing. I have a friend who did this to the little header on his Fiat 850. You can almost touch it after everything is up to temp.

 

I recall working on Jag XKE's years ago, they had these wonderful ceramic exhaust manifolds. I dont know as I would attempt touching one after a run, but they were sure pretty. The next question is what coating to use, the 1300 degree F, or the 2450 degree F. I know some of you have mentioned the headers running red hot after driving, I wonder if the 1300 coating is acceptable.

 

on my 80 308gtsi the headers coating is by jet hot. to me thay are the best.

 

Exhaust gas temps of 1400F are not uncommon - so 1300 F would be marginal. Although the header material may not be that hot, it is better to be safe. HP Coatings basic header coating is good to 1600F. Their next level is rated at 2000F and would be appropriate for a turbo manifold.

I do not sell or represent HP Coatings, but I have never heard a complaint about their coatings. I work in the exhaust field.

Vince

 

Had a couple of XK150 jags w/same coatings. Classic porcelan. Sure looked nice if they'd been kept clean, but a bear to get cooked on oil off of w/o scratching them up. Did seem to keep the heat way down. However, the metal under them was thick cast iron. Rugged tho.

Was hoping the Jet-Hot would look like them, but the satin black isn't anywhere near as heavy a coating.

I went with the 1300F jet-hot, am hoping it isn't too marginal under spirited highway driving. I don't plan to heavily track the car, & can't afford risking a big time speeding ticket in NE.

If the gas temp is coming out around 1300F-1400F, I'd expect a cooler boundary layer a few hundred degrees coolar around the header tube surfaces. Hopefully just enough cooler to stay within the coating's specs.
Will keep a watch on it. Guess if it looks like it's degrading I'll send it back to be stripped & the 2300F coating put on.

Hmm, if I remember right, iron glows noticably red up around 1300F or so, & dull red at about 1000F? I've never seen my cars headers glow at all, even after a long highway drive.

 

So if the header coating drops the skin temp by a claimed 40 - 50%, they shouldnt run anywhere near hot enough to be a factor?

 

I spoke with the guy who used Jethot for his 850. He got the "chrome" or silver color option. It didn't last very long. It started to pit or something on the surface so he returned it to them. They removed it by sandblasting (or it appears they did) and changed it to black which has made the surface appear rougher then before. They charged him for the redo as well.

Jet hot is a good choice but probably not the silver color.

 

I had the headers on by Boxer cermanic coated in silver by Miller's Powder Coatings(770.931.1505) and over two years later it still looks like the day they did it. And, it only cost $300.00.