The biggest difference I noticed between the biturbo exhaust and the stock exhaust on my targa was that the stock pipe wound way to the left after leaving the cylinder and then came back to the right side of the bike. The biturbo just curved straight down and back to the right on a angle that aligned with the rear muffler mounting bracket.
Also, the inside diameter of the biturbo was at least 1/8 inch larger.
And also, the diameter of the exit pipe on the biturbo muffler was about 3/4 inch where the stock was about 1/4 inch.
Maybe all this is relavent to this type of bike only, but it sure as hell sped the beast up. A little more torque and a ton more level / downhill speed.