The 400ex is capable of making 40+ H.P. when big bores and stroker cranks are used. Standard clutch kits will not last long with that kind of power. We designed a clutch kit to handle the abuse of a higher H.P. engine, we took our std heavy duty kit and added a stiffer set of springs. The clutch pull is stiff but not so extreme that hand fatigue is a problem. We also recommend this clutch kit for dune riders. Sand dunes are very hard on clutches and can cause the same wear that a high H.P. engine can cause. This kit is designed for a Honda 400ex all year models . We use cork style friction plates which are proven to be very durable. Smooth steel plates & springs that are 10-15% stiffer than stock. One of the durability keys to our clutch kit is the smooth steel plates. "Dimpled or textured" steel plates WILL NOT handle as much H.P. or last as long as smooth steel plates. "Dimples" are concave in shape which reduces surface material causing less contact area which results in premature clutch slippage.