On an early test run the R engine produced 1,400 hp (1,040 kW) and was noted to idle happily at 450 revolutions per minute (rpm). With increased boost ratings and fuel developed by Banks, the R engine ultimately developed 2,530 hp (1,890 kW) at 3,200 rpm; well over double the maximum power output of the Buzzard. The engine was further tested and cleared for limited sprint racing at 2,783 hp (2,075 kW) at 3,400 rpm and +21 lb (1.45 bar) of boost, but this capability was not used due to concerns with the S.6B's airframe not being able to withstand the power, and the inability of the aircraft to lift the extra fuel required to meet the increased consumption.