Due to the higher cylinder pressure in 4-stroke engines, pistons are generally made from forged pieces. To withstand the internal pressure of the engine, VERTEX pistons are forged from the highest quality aluminum alloy (2618). Each VERTEX piston features an MOS2 coating on the piston skirt to reduce wear. VERTEX is an OEM supplier for some of the largest motorcycle manufacturers, and many factory teams in MXGP rely on VERTEX's performance. The kit includes the piston along with piston rings, piston pin, and circlips. The 4-stroke piston design includes Pro Replica, which is a forged piston matching the original form, and Pro HC, a forged specialty piston with higher compression and performance enhancement. Note: Compression Ratio 13.5:1, suitable for EXC(F), FE, EC(F) models!