TonyB,
Just a thought; coat the inside, polish the outside. If I remember correctly, from reading many many years ago, coating of the inside of a header helps flow the heat thru and out of the exhaust system. But ether way, the coating will help deture rust that will start where the SS is welded.
Joel

 

Sorry, I can’t upload pictures from this location but here are some links https://www.northamericanmotoring.co...9649&nocache=1 and don’t forget the heat shield https://www.northamericanmotoring.co...0&ppuser=13976
It’s ok to coat the cat as well as long the openings are plugged. The problem with coating carbon steel is that rust never sleeps entirely; it will still rust through, it only takes a little longer. I wouldn’t be too concerned about the 2.25 exit from the cat. Gas temps will be higher due to retained heat so velocity will be up as well.

I know Tony has seen this one but if you want to go hog wild do the entire exhaust system https://www.northamericanmotoring.co...0&ppuser=13976 . There was a defective weld on the Y-pipe and I had to take this apart after using it a month. The coating made for a very snug fit which meant disassembly was very difficult (I tore a muscle in the process). This gives me an opportunity to trash Borla’s warranty performance; 4 months and the part has yet to be replaced. Borla “it will take 3 weeks”, “it takes a long time”, “we lost the returned part”, “the request never made it to production”, “it will be the end of the week”, “it will be sent the end of the following week”, “you should have it the week after next”.

 

Keith, some of us are **** about weight-reduction, and others with heat management. You are indeed the later . I truly mean that in a good, envious way though...

I appreciate you commenting on 2.25" section, and your reasoning makes sense. I will stay with it. And I like your idea about coating the cat, so long ast the opennings are covered. Is it possible/feasible to coat the inside of the outlet tube (the 2.25 portion) of the cat w/o getting any inside the cat itself? Great idea on doing the heat shield also! After coated, is it still somewhat malleable?

The thought of doing my whole system crossed my mind alright, especially since it is short/straght - I'm guessing it would be easy/cheap to do. If I do this, I will be when I have scheduled down-time, like when a ditch the A/C. The nice thing about coating this header/cat combo is that I will have no down-time...

Oh, before I forget, from your gallery, did you also have the header flange coated, even the surface where it mates to the head (looks like it)? I sort of thought that this might not be advisable? If you coated those, I'm guessing that the whole header should get coated, but maybe not the joint area where it joins the cat. I would appreciate some clarification there... Thanks for your time Keith!

Hey Joel, thanks for your input also. If I get this coated, and I'm certainly leaning that way, it will be inside, and out. And as someone said earlier, a thinner coat on the inside as to not take away too much volume...

ArmyDog, thanks for the JetHot mention. I've heard of them alright. If I do indeed ship this header, it will most likely be to HPC; but I'll check JetHot again...

 

I have used JetHot before on my hod rods in the USA. The coating is great, the customer service is good too. I was thinking of getting my Supersprint header coated too....

 

Since I never dyno'd anything back then I can't say about HP gains but I do know I had to mess with fuel mixtures, it was definitely cooler under the hood and there was a mild change in sound.
This was over 20 years ago so please forgive the vague recollection

 

Different coatings have different properties; the silver coating on that header is very flexible so that’s why it was chosen for the heat shield and entire header including the flex joint. The silver coating required a burnishing process after the coating was applied & cured so the flex section had to be masked as well as all openings to protect the cat once again; otherwise there would have been little white bb ***** stuck in everything. Yes the flange is coated, but first it was de-burred, inspected for trueness, port matched, and the off center primaries cleaned up. For both the primaries and cat O2 tube the coating was applied a couple of inches within the interior. Seek professional advice on what to do about your donut section.

As a general rule for ceramics the black coatings are superior to the silver ones for heat retention although they are usually thicker and less pliable and there are other ceramic varieties. I know Mike (namwob) likes multiple varying coats.

One unexpected feature of coating the entire exhaust system was the alteration of exhaust note. At first start-up idle sounds wonderfully low and mellow, then after it gets very hot, idle sounds woody like boards slapping together, not very pleasing (this is standing outside behind the exhaust). At high revs there is a definite reduction in interior resonance and it doesn’t have the woody sound that can only be heard outside of the vehicle.

 

This has become very educational. Thank you Keith. I see why although you chose black for the catback, why you went with silver pre cat... Multiple varying coats, I'm assuming different colors maybe. I will definitely seek a professional opinion on the ball joint area. At least now I have quite a bit more knowledge so I can ask more intellingent questions, and understand better...

I guess I need to hear what you mean by a "woody" sound... I think I know what you mean though. If it is on the outside, I'm fine with that. At higher RPMs, I like the idea of less internal resonance...

Thanks Keith. I'll report back once I proceed with coating...