Adam - Ambient is just a fancy word for "don't include wind chill"..haha. How ya been? Do you still have AIM?
Bad Attitude - The P2K2 is a 27 turn stock motor. Which car do you have that came with a 19 turn? Sometimes the stock motors in RTR cars aren't very strong..but some are.
CTRJ - There was a Worlds Edition XX4, so there are all of Losi's hop-up parts for it. X-Factory makes the X5 single belt conversion for the XX-4. Make sure you take care of your belts and you'll be fine.
local racer - Last I heard, he raced for Panther and Jake-A-Fied motors..
Dave - A smaller gap will give you less bottom end. I usually have about 1/4 inch gap between the header and pipe. Pipe and header length also make a huge difference in powerband, so it's not just the gap that changes things. Don't ever let the pipe and header hit each other, or it can cause you car to glitch.