05.08.2010, 12:14
Here is a pretty in depth write up on supercharging and turbocharging and worth the read. He does not cover the combination of the two but still worth the read.
http://www.aerosuperchargers.com/Docume ... o_3.31.pdf
And somemore that speaks of the lack of oomf at the upper altitudes.
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 built by Packard as the V-1650 and used in the P-51B Mustang and subsequent variants. The US Army 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 turbosupercharger as was featured in the P-37, P-38, and XP-39.
The benefits of a two-stage supercharger eventually became so clear cut 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 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). 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 anti-detonation injection 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 one hour of flight.[1]
http://www.aerosuperchargers.com/Docume ... o_3.31.pdf
And somemore that speaks of the lack of oomf at the upper altitudes.
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 built by Packard as the V-1650 and used in the P-51B Mustang and subsequent variants. The US Army 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 turbosupercharger as was featured in the P-37, P-38, and XP-39.
The benefits of a two-stage supercharger eventually became so clear cut 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 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). 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 anti-detonation injection 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 one hour of flight.[1]