Generally, any of the insulating wraps will raise the temp inside the pipe and thus
speed up the wave activity inside as well. This will cause the wave activity to be
efficient at a higher rpm than before and raises the powerband (usually narrows it a
tad, too). If it is jetted and timed complimentarily, there is usually an increase in
power at the new, somewhat higher peak rpm. Depending on how far down the pipe
it is wrapped, there is often a corresponding loss of low speed power. You see this
trick on drag racing vehicles quite frequently because they are trying to build up
heat in the pipe quickly to match the high rpm that they will be finishing their race
up with in just seconds. (The other big deal with header wrap for the car guys is
that any reduction in underhood temp means a cooler and thus denser intake
mixture.) If it is done correctly, in these situations it can be used as a sort of
pre-timed, variable exhaust system. But because too much heat wrap can cause
temps to go too high in extended use situations, you should be very sparing with
heat wrap until you have verified it to be safe for your length of time of operation.
Expect to need more main jet and quite likely more mid range fuel as well. You may
have to limit ignition lead a bit, too. Good luck.