DRZ400 Big Bore Kit: kit assembled with OE CDI and exhaust gets much more torque (Nxm) than OE bike; in order to strongly increase horsepower to the wheel, it is necessary to use, at least, a racing exhaust system. YZ125 Works Kit: YZ125 97-98 models require the use of a 99 or newer exhaust pipe and silencer. YZ125 Race Kit: To use on 97-98 models you must use a 99 exhaust and an 01 cylinder head; for 99-00 models you must use an 01 cylinder head.