Exhuast
#11
For a stock 6.5, 3.5-4.5" exhaust is perfect. For the best flow make sure the tubing is the same diameter throughout and not small in the bends. With no muffler or cat it will be the best flow possible. If your state mandates that you have a muffler, I suggest getting an Aero-Turbine brand muffler. They are very good and have great flow qualities. Also, there are a few companies that make a larger than stock diamter exhaust crossover pipe, it helps immensely. With all of that done you should see a gain of 5-15hp.
#13
#15
Sorry to burst your bubble but, no. It depends on the muffler you use. Stock vs straight is a huge difference. But Glasspack vs straight is almost the same. Get what I mean?