i got two 40s and need to know the best way to have them installed to get max sound.. thanks

 

I like dumped exhaust. it seems louder to me, but I bet someone around this place with more experience could help you more than I.

 

Assuming ur 40s are SI/SO you are set! This is what you do. If you want the loudest, then dual it out, meaning cut the factory y-pipe off and run 2 parallel pipes into ur 2 FM 40s.No X,Y,H- pipes, that will only quiet it down, then after the FM 40s, its free game. For the loudest, it has to be dumped or some big tips comin out infront of the wheel like the lightning. Since you have a 4.6 some would reccomend running 2.25 inch pipes, but I think 2.50 should be okay and its a little louder.
Good luck