The result was a Bristol Mercury-sized engine adapted to the sleeve valve system, the Perseus, and its smaller cousin, the Bristol Aquila. The first production versions of the Perseus were rated at 580 horsepower (433 kW), the same as the Mercury model for that year, which shows that the sleeve system was being underexploited. The engine was quickly uprated as improvements were introduced and by 1936 the Perseus was delivering 810 hp (604 kW), eventually topping out at 930 hp (690 kW) in 1939, while the Perseus 100 with an increased capacity of 1,635 cu in (26.8 L), produced 1,200 hp (890 kW) at 2,700 rpm at 4,250 ft (1,296 m).[3] This far outperformed even the most developed versions of the Mercury.