the set that I made stayed 1 5/8 because the 1 7/8 was just a little too tight for my liking in the early narrow body (and my limited fab skillz), and kept the "collector" at 2.5 because of the 4spd things and stuffs. but I also wanted something that was easily serviceable.
it would be quite interesting to see a bigger tube shorty, especially on a mill that was spec'd out for upper RPM operation
