An L-ring (a piston ring with an L-shaped cross section) has been used on some air-cooled two-stroke gasoline engines. Good performance has been obtained; the reason is unknown. The maximum power of these small engines (used mainly for small cars, motorcycles, outboard motors, snowmobiles, etc.) is limited by its thermal load endurance. So piston and cylinder become the most important factors to the engine's performance. L-ring effects are examined in the light of these temperature measurements.