Stroke is the distance the piston travels up or down on the cylinder walls. We have "square motors" 86mm bore X 86mm stroke. Square motors with small strokes have potential to rev really high. The K24 block has a 99.0mm stroke which is massive and Honda stamps a 6500 (Or 6800?) redline on it for all K24s except the TSX which is at 7100 RPMs.