We recently installed our FMF PowerCore4 Performance Exhaust Package on one of our DRZ project bikes. The package consists of an FMF PowerCore4 Muffler, FMF PowerBomb Header pipe, and we added on the optional JD Jetting Jet Kit, and K&N Hi Flow Air Filter. We've also done the 3x3 airbox mod commonly seen on these bikes. Last but not least, we bolted up a Z Carbon Universal Pipe Guard to the header pipe for some extra protection.
The FMF PowerCore4 Performance Exhaust package makes a huge difference in the DRZ's overall performance. Our DR-Z400SM Project Bike is now way more fun to ride.... it pulls much harder than it did with the stock exhaust, and the powerband feels more linear. From a sound standpoint, the PowerCore4 muffler is slightly louder than the FMF Q4 muffler we have on our other DRZ, but it sounds great and has a nice deep tone to it. IMHO it's just the right noise level if you have a DRZ400SM supermoto that you ride mostly on the street or at the track. If you have a DRZ400S and do more off-road riding, I'd lean towards the FMF Q4 package since the Q4 muffler is a little quieter.
Video Overview with Sound: