header wrap

[Lines Peter]

Header wrap or a thermal barrier coating (i.e. ceramic) on the outside will
cause the metal to run hotter.  This is because the hot exhaust gases are
still adding the same amount of thermal energy (heat) to the metal, but the
metal can't reject the heat as quickly due to the coating.  This will reduce
the underhood temps at the expense of header lifespan.  If you want to lower
the metal temp and improve header life, then coat the inside, although this
may lead to turbo problems if the coating comes loose.  The headers will
last longer if made from stainless rather than carbon steel.  There are
several things that make stainless a good header material.  Obviously it
doesn't corrode as much so they look better.  Stainless also has a lower
coefficient of thermal conductivity.  This means it doesn't conduct as much
heat which lowers underhood temps and holds more heat in the exhaust.  The
stainless has a lower coefficient of thermal expansion so it changes shape
less under high temps and don't crack as much.  Lastly, stainless maintains
its strength at higher temps which also contributes to longevity.  The
downside of stainless is cost and it can be more difficult to weld, although
any good TIG welder should be able to deal with it.  Keep in mind this stuff
is all relative.  A coated carbon steel header may insulate better than
stainless, but you need some thermal property data on the coating, the
carbon steel, and the stainless to make this determination.  If money is not
object, make it stainless AND coat it!

-Peter Lines