Am putting together a grunty naturally-aspirated engine for my EF XR6. Have noticed that intake air temperature has a dramatic effect on performance. I have a phenolic insulator to reduce heat conduction from the head to the manifold. But the engine bay is a hot place, and the intake manifold can get quite hot, warming the incoming air and reducing power.

So, before I put it all back together, I want to do what I can to reduce this heating. I am tossing up whether or not to polish the outside of the intake manifold to minimise the heat getting in.

Aluminium is a good reflector of heat - from about 70% reflectivity for heavily oxidised, up to 96% for highly polished. So, a polished manifold should pick up less radiant heat. But aluminium is also a great conductor of heat. And polishing would significantly reduce the surface area, so there should be less surface available to conduct heat from the engine bay air.

In my head, the science is saying to polish the manifold. But, I'm not a scientist, and could have it all wrong. Is there anyone on the forum with experience of what happens to intake air temps and power when you polish the exterior of the manifold?

Thanks.