The best pipe I have seen for the big block was the Rick Ritter pipe. It looks like a banana smoking a stogie. I picked up a Ritter pipe 15 years ago. It is a hydroformed expansion pipe but it doesn't have a muffler so it is really loud. Works awesome, turns a savage into a wheelie machine...
Why would a hump pack be faster than 4 AA's? They are both 6 volts. Alkaline AA batteries are 1.5 volts per cell and NiMH cells are 1.2 volts per cell. So 4 Alkaline's cells = 6Volts and 5 NiMH cells = 6 volts. The only time that the hump pack will be faster is if the servo draws more current...
I have a little mod that I do that helps transfer heat from the head button to the cooling fins. Just add a thin smear of heat sink compound on the top of the head button before bolting the fins on. This will increase the rate of heat transfer between the two parts. I use Arctic Silver paste but...