Quote Originally Posted by Matt167
manifold temp has to be at least 500* ( and 650* to be accurate ) for an O2 sensor to run in closed loop, so it's gotta be hotter than that under break in?
Think he's talking the external temp of the metal, not the temp of the exhaust gas, Matt.....

IMO, 375 for ceramic coated or stainless headers is a bit high... With an ECM, probably not a heck of a lot you can do about it though... Sounds like you're going to have some blued headers..... Might as well get some header wrap, the high underhood temps won't be doing anything good for the performance of the engine.....