the installed lifetime of the engine to be increased from 300 hours to as much as 1,000 hours for the less-stressed power-plants. Weight increases needed to accomplish this were minimal, with the result that all models were able to produce more than 1 hp/lb (1.6 kW/kg) at their takeoff rating. Comparisons between the Allison V-1710 and the Rolls-Royce Merlin engine "families" are inevitable. What can be said for the Allison is that it made more power at less boost, with a longer time between overhauls, and with a parts-count that was nearly half that of the Merlin engine, which greatly facilitated mass production. There was also a high degree of commonality of parts throughout the series. The individual parts of the Allison series were produced to a high degree of standardization and reliability, using the best technology available at the time. Even after the war, racing Merlins used Allison connecting rods. As stated previously, General Motors' policies regarding versatility meant that their Allison division would also employ modular design features on the V-1710 from its "long block" core V-12 unit outwards, so that it was capable of being mated to many different styles of turbo-superchargers and various other accessories, although the variety of turbo-superchargers available for installation was limited due to the constraints of single-engine fighter design. Since it was produced in large numbers and was highly standardised, the engine has been used in many postwar racing designs. Its reliability and well-mannered operation allowed it to operate at high rpm for extended periods. Following the war, North American built 250 P-82E/F for air defense roles into the early 1950s. This was the final military role for the V-1710. Turbo-supercharger The USAAC had earlier decided to concentrate on turbo-superchargers for high altitude boost, believing that further development of turbo-superchargers would allow their engines to outperform European rivals using displacement superchargers. Turbo-superchargers are powered by the engine exhaust and so do not draw much power from the engine crankshaft, whereas displacement superchargers are coupled directly by shafts and gears to the engine crankshaft. Turbo-superchargers do increase the exhaust back-pressure and thus do cause a very small decrease in engine power, but the power increase due to increased induction pressures more than makes up for that decrease. Crankshaft-driven superchargers require an increase in directly driven percentage of engine power as altitude increases (the two-stage supercharger of the Merlin 60 series engines consumed some