I went to look at an S40 that I may be getting, and it sounded pretty quiet. Does anyone know of any good pipes that will make it louder? I really want it to roar.

 

I took the baffle at the end of the muffler out of my s40 and gave it a pretty good sound. I would suggest re-jetting your carb if you do this or your bike will run too lean. You can buy after market pipes but it will cost you.
Hope this helped.....

 

I have an 07 s40 that i bought last year with 700 miles on it when i bought it the person before me who had it had drilled the baffles out of the exhaust and personally no offense to anyone i would not reccomend that the bike ran like crap and was way to loud also even though these bikes are prone to backfiring this made it 100 times worse and for me almost unbearable to ride. So i went on ebay looking for an exhaust and found a nice used supertrap muffler so i bought it and put it on and it is really nice. You can add or subtract rings which will make the exhaust louder or quieter which is nice because you can custom make the sound you want. This also helped with the backfiring and made the bike run better. I also had the first service done and they adjusted the valves and this made it like a whole new bike fixed most of the backfiring and the bike waas stronger and smoother. Also the supertrap for a sportster will work. Hope this helps