Owing to non-availability of other good quality 998cc pistons, these Mini Spares Evolution design pistons from a renowned high-performance piston manufacturer are flat top with drilled oil drain-back holes rather than slots behind the rings for maximum strength. The flat top, non-slipper design, with high silicon content material and specialised heat treatments makes them suitable for any engine, whether road or race, at a very competitive price. Suitable for up to 12.5-1CR. They will give a compression ratio of approximately 9.6:1 (dependent on bore size) when used with a Cooper cylinder head. This piston replaces the original Hepolite pistons 18516KR and P20950 used on the original 998cc Coopers. Do not mix with Hepolite type as they are not a dimensionally direct replacement. Only fit in complete sets of 4. To use with later press fit type con rods just discard the circlips.