Objective: Generate additional power by inducing higher compression in the cylinder. Translate more of that ignition power into mechanical power with lighter & shorter high-compression pistons.
Modifications: Stage II + High-Compression Pistons
Pros: Higher compression allows more fuel-air mixture into the cylinder and allows for a longer stroke - thus generating more power. Performance is enhanced at low rpms and the motor can accomodate a more aggresive cam timing.
Requires: Engine work (8-9 hrs avg) to install new high-compression pistons and rings + Dyno-tune - which is expected to deliver higher torque & horsepower, more efficient combustion (which may lead to better fuel economy), cooler engine running temperatures, and better throttle response.
Cons: Requires serious and professional engine work. You will never want to ride a stock bike again!
After a Stage III modification your bike may need a number of additional modifications, not specified in any one stage since it will depend on the specific parts, previous modifications, your engine and the miles on it. These modifications could include lifters, push-rods, valve job, valves, valve springs, cam plates, oil pumps, clutch kit, etc. One modification that is highly recommended after a Stage II is a heavy-duty clutch spring since the power generated will put a lot more pressure on your clutch.