enginehistory.org

[avasko]

The V-1710 suffered greatly from its original customer requirements. Airship engines did not demand great amounts of supercharging. The Air Corp's fascination with turbo-supercharging probably limited Allison's interest in spending time on developing multi-speed and multi-stage engine driven superchargers.
It's later development of a multi-stage supercharger was a remote unit driven by but not part of the main engine.
Somewhere back in my dim memory banks I remember reading that someone? fitted a RR Merlin two sped two stage supercharger to an Allison V-1710. It must have required an adapter to fit it, a very complex one.
Could it be done? Mechanically I men.
Was it done? Actually, or only a proposal?
If it was done, how effective was it?
Seem to remember it was squashed by GM with Air Corp help.

Remember that the two-stage engine (production) was first done by P&W for the Grumman F4F. Did Allison miss an opportunity to make the Curtiss P-40 and Bell P-39 better at altitude? Without a turbo.