Air flows with less restriction over a hot surface, therefore wrapping your down pipe will increase flow. Air temp will also be reduced underhood, harmonic resonation will be reduced (ie: it will be quieter, with less or no drone) Wrapping from the elbow down (including the elbow) 3-4Ft should do the trick. Stainless Steel safetywire is the hot set up for keeping everything wrapped up nice. Don't forget to get some of the headerwrap silicone spray to protect it from moisture.