Going back to science, the black plastic has 2 main functions of heat transfer. There is conduction and radiation. Convection does not exist as the medium does not move. So although plastics are already relatively good insulators of heat, the black surfaces readily adsorbs heat and radiate heat. We insulate the plastic against this absorbstion with a silver aluminium foil that is backed by fiberglass wool. Why only the air box? Cos the air box is the largest volume, compared to the tubes leading to and from the box, which means the air speed drastically slows down to allow it to pass through the air filter. Hence when it slows down, there is alot of time for the radiant heat to interact with the air, thus heating it up.
Why do engine mounts affect performance. All engines produced a fixed amount of power/torque. If your engine rocks when you rev, the energy has to come from the crankshaft. And this means that there is less going down to your transmission and driveshaft. with stiffer mounts, less torque is lost to engine movement.
There is a drawback though, that is you get slightly more vibration going into the cabin.
cheers
