We've installed and thoroughly enjoyed the HKS Preminum Axle Back system on our own ND but if you're looking for something to open up the system a bit more the full stainless Invidia N1 system is about as nice as it gets. The mid-pipe included with this setup is top notch and everything is straight through. Install was just under an hour, including the removal of the Goodwin RoadsterSport Race Helmholtz system. After a quick wipe down we fired her up and she rolled out of the shop, packing a bit more audible punch.