I wanted to redo the finish some of the aluminum parts in my engine compartment to match my car's paint. All of the parts are exposed to heat (air plenum, exhaust shield, etc.). Does anyone know if either anodizing or powdercoat will stand up to the heat?
If the aluminium is low quality, the parts will turn out very dull through anodising. It would be easier to match your car's exterior paintwork by having the aluminium engine parts powder coated. Baking is involved in the process so heat that's generated by the engine shouldn't be a problem. You should be able to get proper engine lacquer as another option but you won't have the same choice of colour as powder coating. Your options could just be something along the lines of one shade of red, yellow, blue, silver and black.
Will the powdercoat act as an insulater, and cause any problems with the air intake?
Yes powder coating will act as somewhat of an insulator but should not
cause major concern on an intake. Depending on the color of the powder
coat you can expect some discoloration if it is to close to the exhaust.
Anodizing would probably hold up better but is fairly cost prohibitive. Additionally before anodizing the part needs to be polished and that causes heat not to transfer as well so in effect is also an insulator.