I'd advise against making something "cool looking" If you want performance. There is a lot of science behind developing a nitro rc exhaust pipe, lengths, chamber sizes, all sorts of stuff. Making your own that looks cool will greatly reduce performance and ease of tuning and cause more headaches than it's worth.
A tunes pipe works with the reverberation and the motor firing... Its suppose to feed fuel into the motor with the rpms almost in a harmony if I am understanding all I have read correctly. This is Def something you CAN do... But it's not something you're going to do without a LOT of trial and error if you're gonna get your pipe/motor working right. I agree with @ninnon here.