Editing Allison V-1710 (section)

===Supercharger===

The V-1710 has often been criticized for not having a "high-altitude" supercharger. The comparison is usually to the later, two-stage, versions of the [[Rolls-Royce Merlin]] 60-series engines also built by Packard as the [[Packard V-1650|V-1650]] and used in the P-51B Mustang and subsequent variants. The USAAC had specified that the V-1710 was to be a single-stage supercharged engine and, if a higher altitude capability was desired, the aircraft could use their newly developed turbo-supercharger as was featured in the XP-37(YP-37), P-38, and XP-39.

The benefits of a two-stage supercharger eventually became so clear that Allison did make some efforts in this direction. Allison attached an auxiliary supercharger in various configurations to the existing engine-mounted supercharger and carburetor. Early versions of these two-stage supercharger engines were used on the P-63. No intercooler, aftercooler, or backfire screen (flame trap) were incorporated into these two-stage V-1710 engines (except for the V-1710-119 used on the experimental P-51J, which had an aftercooler and Flame Traps). The two-stage Merlin engines had all of these features, which were designed to prevent detonation from charge heating and backfire into the supercharger. The G-series V-1710s installed on the [[F-82]] E/F/G models had only [[Water injection (engine)|anti-detonation injection]] (ADI) to deal with these problems, and not surprisingly had severe reliability and maintenance problems. In one record, it was stated that the F-82 required 33 hours of maintenance for each hour of flight.<ref name="Wagner">Wagner, Ray. ''Mustang Designer: Edgar Schmued and the P-51''</ref>

Although the early V-1710 powered P-39, P-40 and P-51A were limited to combat operations at a maximum of about {{convert|15000|ft|m}} they were available in comparatively large numbers and were the mainstay of some Allied Air Forces in all but the [[European Theatre of World War II|European theater]] of war. The engines proved to be robust and little affected by machine-gun fire. In total, over 60 percent of the [[1941 in aviation#June|post-June 1941]] [[USAAF]]'s pursuit aircraft operated during WWII were powered by the V-1710.

Allison slowly but continuously improved the engine during the war. The initial rating of {{convert|1000|hp|kW|abbr=on}} was incrementally increased; the final V-1710-143/145(G6R/L) was rated for {{convert|2300|hp|kW|abbr=on}}. By 1944, the [[War emergency power|War Emergency Power]] rating on the P-38L was {{convert|1600|hp|kW|abbr=on}}.

The most powerful factory variant was the V-1710-127, designed to produce {{convert|2320|hp|abbr=on}} dry at low altitude and {{convert|2800-2920|hp|abbr=on}} at {{convert|33000|ft|m}}. This engine was static tested at {{convert|3090|hp|abbr=on}} wet War Emergency Power and was planned for installation in an XP-63H aircraft. The end of the war ended this development, so this promising experiment never flew. The extra power of this version was derived from using exhaust turbines, not to drive a turbo-supercharger, but to return that energy to turning the crankshaft, called a [[turbo-compound engine]]. (From Aerospace Engineer Jim Leonard's Monograph dated 2010.)

Improvements in manufacturing brought the cost to produce each engine from $25,000 down to $8,500 and allowed 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&nbsp;hp/lb (1.6&nbsp;kW/kg) at their takeoff rating.

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 standardized, 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-82]]E/F for air defense roles into the early 1950s. This was the final military role for the V-1710.