This K4 is an evolution of the very good K53, on which the drivers' comments have been applied. New features include new crankshaft with revised diagrams for more torque and reduced fuel consumption 2 balancing inserts for increased torque. New liner with revised diagrams to match the new crankshaft, again for increased torque at low revs. The rest of the engine uses the same components as the K53. Ceramic bearings, machined piston, 8mm carburetor with 3 aluminum nozzles (6, 6.5 and 7mm), T3 spark plug. Recommended Pipe: 2159 Argus (AG-21K4)