Stage 1 is intended for motorcycles with a stock engine using the stock airbox, air filter and stock pipe. Stage 1 kits are fully adjustable to allow the use of a well designed aftermarket pipes and stock replacement air filters like K Stage 1 kits are designed to improve throttle response and drivability and in most cases power increases of approximately 5% throughout the entire power range can be achieved. Stage 2 is intended for motorcycles with a stock or mildly tuned engine using a well designed aftermarket pipe with a modified airbox and a stock replacement air filter. Stage 2 kits are designed for applications where individual filters cannot be installed and for applications where airbox modification improves the engine's performance. In most cases power increases of approximately 8% can be achieved.