you can get a good highflo cat just about any muffler shop around your area for around 100ish, and have it welded into the test pipe for a bit more...but no matter what, youre gonna get quite a bit louder...however, i have just a silencer on my HKS exhaust and its not much louder than the intake/ehaust combo...so im sure if you get the RB and a high flo cat you should be pretty happy with the results, both power wise AND sound wise