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WE should be designing superchargers for better overall efficiency, according to Mr. Pigott, because the effect on engine capacity is pronounced, and gets to be more so at higher boost pressures. Mr. Pigott shows also that supercharger performance can be rather well predicted without trying out a variety of blowers in expensive engine setups. He sees no reason to suppose that the newer adiabatic rotaries can be considerably improved as they are further developed. He adds that the Roots type has seen considerable development and will be at the end of its string when boost pressures exceed 7 or 8 psi, which they are certain to do in the future.

WHILE the centrifugal supercharger is excellently suited to aviation service and to relatively constant-speed, diesel-engine service, Mr. Pigott states, it is not of value for cases of considerable variation in speed where full boost is required at all speeds. The Roots-type blower, the author says further, has had a justified development for low-pressure boost, but is not valuable for compression ratios much in excess of 1.6 because it has no adiabatic compression. The vane-type supercharger, while it has an adiabatic compression, as so far developed appears to the author to be somewhat complex in structure, requires internal lubrication, and has not yet shown satisfactory efficiency compared to other types. The Elliott-Lysholm screw-type and the new P. L. internal-gear type appear to him, however, to give great promise for satisfactory supercharging at the higher pressures beyond the range of the Roots type, and appear to be the best present line of development.