Standard pipes!
I just set up a microphone pointing down and backwards from the camera with a double windscreen on it to try and get something like the "feel" of the exhaust note. First time I'd tried video recording so just left the sound level on auto though I suspect that it would be better setting it manually after a bit of playing around to find what works.
Don't honestly think I would want pipes that were any louder than standard; there's a bit of a limit to how many ear plugs I can wear.