Depends on the kit you get, for an 01, they should all bolt up unless you buy a 15+ kit with the flange. Your options are probably going to be limited by the EPA crackdown, i have a MBRP kit, and while its not amazing, it does what it needs to do, and for a fair price. I have heard the flo pro kits are better, but there also hard to find right now.I have a 2001 Chevy with everything factory and I am wanting to put a 4" straight exhaust on it. Will it bolt directly to the factory down pipe or do i have to change it out. What are some good exhaust kits to use.