Started out by putting a FMF Power Bomb header on my '06 CRF 450 but I didn't notice much difference at all. Followed up by putting on a full FMF Power Core 4 exhaust on. It mounted easily. It made a very noticable increase in power, much more so then the FMF header did. More significant of power increase when in the lower RPM's if the spark arrestor is out. Louder then stock but not to bad. It's holding up good except for the decals having a tendency to peel back.