State of supercharging.
At altitude of 14000 ft, the max boost was for the FS Mercury was +5 psi, while the Pegasus in FS gear was good for +5.5 psi at 15500 ft. Perseus FS version - +3psi at 15500 ft. Seems decent, until we look at impeller's diameter. Mercury - 10.75in, Pegasus 11.25 in for the FS versions, or, in other words, the respective impellers were huge. Perseus - 9.25 in. All this is for
The 9.5in impeller on the V-1710-39 was managing ~39 in Hg, or +4.4 psi at 15000 ft, the same impeller on -81 and the like gave +6.7psi there. Nobody was heaping praise on the supercharger of the V-1710 engines (with good reason), but Britstol's superchargers seem to be really bad.
Problems, at least when accompanying Calum's book with
stuff found here, looks to me as coming from few important details. Like forcing the incoming air to fight it's way before finally entering the impeller, and lack of the curved vanes preceding the straight vanes. (
see here for how the curved vanes might look)
So the order of the day should be clearing the air passage right before the impeller, and designing the separate curved vanes that can be attached to the impeller front. Hopefully we'd get same result as the later R-1820s or mid-war Sakaes and Zuiseis - 42-43 in Hg at 18000 ft, or +6 to +6.5psi. Or, perhaps 950-1000 HP at 18000 ft.
A better and more efficient supercharger together with better fuel available to the British should make useful power at lower altitudes, too.