Maao said:Ah crap. I wish I knew this before I had them JetHot coated.
Now I don't feel so bad. I got the JetHot 2000. And the inside has a very thin coat. Supposedly it's guaranteed not to crack, and if it does, they'll recoat them.houstonT said:Anything you can do to retain heat and keep underhood temps down is a good thing. I would DEFINATELY coat the header. Use Jet Hot 2000, that shit will never come off....
p.s. expanding of a stainless steal .25 inch thick header? No chance guys, 1600 F is not enough make it expand in such a way that it will crack the coating. The 1600 is cracking b/c it can only withstand around 1600 F and he has hit more than that...
Jim, there are actually a couple of factors involved...93dawg said:Have you found it to be true or not that a manifold that has been fabricated from many pieces and welded up will crack after extended use, especially a manifold that is bringing together 6 exhaust ports into one outlet and has lots of tight bends and not much room to do all of that bending?
Jet-Hot coats the inside of the header with a 1mm layer of the stuff. Hopefully, if it does start to flake off, it won't be enough material to cause any problems (unless a large chunk happens to fly off!).houstonT said:maao - i was talking about the OUTSIDE being coated, NOT the inside. I would NOT coat the inside though, that is asking for trouble although the 2000 still "should" not crack...
Whoa! amazing drawingFYRARMS said:
Jim, there are actually a couple of factors involved...
a) Material used.
b) Location of welds on manifold.
c) Type of welding used.
d) Skill of welder/fabricator.
My old employer has been fabricating turbo manifolds/headers since 1988. The welder that works for him is a certified welder who used to fabricate NHRA Top Fuel funny car chassis'. In spite of their credentials, they STILL have some manifolds crack! It has a lot more to do with trial-and-error than people think. It is virtually impossible to predict whether or not you will see cracks. Most cracks that do appear are in a V-shaped joint, such as those commonly found in most Supra turbo manifolds. We had great experience using SCH40 T-shaped pipe sections, TIG-welding them, and then sending them out to be ceramic-coated. Our shop Turbo Neon went 9.80's using this type of manifold with NO cracking. Based on my experience, the BEST way to prevent cracks is to manufacture a log-type manifold such as this (excuse shitty drawing):
Correct. Also, many exhaust manifold crackings are caused by engine twisting under load and turbo being pressed against passenger side shock tower, thus putting torsional stress onto welds.turbotoy said:If you are worried about fatigue failures, get the header vibratory stress relieved. This method has shown great success in minimizing residual stress in weldments, which is a major cause of stress fatigue fractures. This is what I plan to do after I finish making the header for my MKIII.