As long as you do not install a power adder, I think the stock exhaust minus the cat and muffler, will maximize our stock systems. The main reason to install a 3.5 inch down pipe and 4 inch back system is if you are planning on installing a power adder. Chip, programmer, propane, etc. There are some mufflers out there that reduce noise, and do not increase back pressure. The stock muffler is very restrictive.