Aftermarket exhaust parts restrictions in the system—can similarly increase performance, though would likely be illegal in areas where tampering with emissions devices is prohibited, particularly when placed in front of the catalytic converters. Aftermarket exhaust parts Aftermarket exhaust parts are intended to replace the factory fitted exhaust components of a car, motorcycle, or other motor vehicle in order to improve the performance, visual appeal, or sound of the vehicle. Generally, performance enhancements are achieved by reducing the back pressure of the factory exhaust system. Frequently a side effect of a free-flowing exhaust system is either a "different" sound, a higher noise level, or
Exhaust system can be made to be quieter than 70dBa at 6000 rpm without sacrificing any power gains. The latest generations of 4-stroke street motorcycle engines that can come close to a 2T in redline RPM but still having the extra weight and inertia of cams and valves make the differences in being "cleaner burning" negligible, with the decreased engine service life to be expected, while also having the sound of a 4T exhaust carrying for miles in many cases. Additionally, "the nature of the beast" is that a 4T exhaust note above 6000 rpm is unduly harsh to the human ear.