A piston for a lean-burn gasoline engine comprising a cylinder, an air inlet and an exhaust outlet, wherein the air inlet and the exhaust outlet are arranged about a longitudinal axis of the cylinder. The piston comprises a central axis which is aligned with the longitudinal axis of the cylinder. The working surface (79) of the piston (454) comprises a central dished portion and an outer sloped portion surrounded by an outer sloped portion. A first pair of valve pockets (444a, 444b) are located in the outer sloped portion on a first side of the dished portion, and a second pair of valve pockets (445a, 445b) located in the outer sloped portion on the second side of the dished portion. The dished portion comprises a ramp protuberance located between the first pair of valve pockets. The dished portion is configured to promote tumble of air flow into the cylinder from the air inlet, in use during an intake stroke of the piston.