I'm sorry I must disagree with the 400 degree statement. Some powders most notably wrinkles, which guys like to use on valve covers, air cleaner housings, etc require a high heat initial shock to start the proper reaction. Additionally a higher mass part may not get to adequate temperature soon enough, or ever get there at 400 degrees.

The cure cycle of the powder specifies the temperature of the surface powder coated, not the ambient set point of the oven. So you should plan on the possibility of running a higher temp in order to ensure the part reaches the required temp.

Light weight sheet metal parts, and smooth glossy colors would normally not be a problem in the 360-380 degree range, but heavier parts, wrinkle finishes and some textures or river textures, may require another 100 degrees.

An example: we used to paint cast aluminum valve covers for an aftermarket brand, using black wrinkle. The set point on our oven was 450 degrees in order to get a consistent surface finish appearance and thorugh cure.