Spit Mk1 Boost?

[JtD]

A supercharger that can produce 12lb boost at 10000 feet (~full throttle altitude for a Merlin III) can produce about 17lb boost at sea level. A fairly accurate estimate is really simple maths, just divide boost at altitude by pressure at altitude in atmos, in this case ~0.7.

Doesn't mean the engine can handle it.

Sea Hurricanes modified for 16lb were not throwaway planes, they were primarily used from carriers with the full intend of repeated use and to my knowledge only from 1942 onwards with the 16lb boost.