What I did
I have the 4 pipe Harley- Vetterman set-up on my -4..ALWAYS get complements on the sound. I have the angled turndowns, clocked with all facing a little inward. As others have said, drumming and heat can be an issue. I did test before floor improvements, barefoot, and it heats up pretty hot when at power. I made a heat shield blankets from RTV matting material (airliner stuff) that I bonded .032 aluminum to the top and glued to foot wells, so it really deadens floor drumming and no more hot floor. Same results from decent carpet...I just don't like carpet, so mine looks like a metal floor.