I needed a 4" MAF pipe for the GN but didn't want to pay much for it (a recurring theme with me..). I bought a $20 mandrel bent 45 degree piece of truck exhaust pipe from the semi supply store, cut it in the middle, rotated it to make an "S" shape, and welded it together. This was one of the first things I gas welded with my Henrob torch. I think ol' Jesse James on Monster Garage makes it look easier than it really is. In a fit of momentary insanity, I took the pipe as well as a turbo shield and up-pipe and had them chromed.