Join Date: Nov 2004
Location: Pacific Northwest
Perhaps if the interior of the tubes was coated comprehensively, but as has been noted it's virtually impossible to prep the surface correctly, so the coating process will be inconsistent, and likely incomplete.
Given the advisory, in this particular application, to NOT coat the inside of the tubes, because of FOD concerns, the coating on the outside will only contain the heat inside the tubes, with no protective quality for the base material.
I'd hazard a guess that only coating the outside, while probably showing some benefit with regards to exhaust gas velocity and energy transfer which will reduce lag, and lower ambient temps proximal to the hardware, will also cause the headers to act as more of a heat sink since the external coating will not allow the heat to escape as readily to atmosphere through convection. I don't know what effect this will have on material life, but my gut suggests that it's probably not beneficial.
Not to mention the inability to make repairs.
I have been wrong before though....