I just installed a FMF Powercore 4 and a FMF Powerbomb header on my 07 DRZ400SM. It's loud and gives the bike more punch. It wasn't cheap (about $410 from RockyMountianMC), but it was worth it. If your intrested, check the magazines (Racer X, Dirtrider, Tranworld) they have $20 off cupons if used before Apr 15, I used all of them ($60 off). You might try making 2 orders, the cupons are generic, and are the same from magazine to magazine. Basically use them twice if they will let you. You will get $120 off that way and shipping will be free on both orders because it is over $100.