One of the great problems, as discerned by pilots was the tendency for the carburetted engine to cut out under negative 'g'. Luftwaffe pilots learned to escape by simply pushing the nose of their aircraft down into a dive, as their fuel- injected engines did not cut out under these circumstances. Many authors have criticised this aspect of the Merlin design. In reality, like most engineering, it resulted from a design compromise. The drop in temperature developed in a carburettor results in an increase in the density of the fuel-air mixture when compared to that of a fuel injection system. As a consequence the Merlin produced a higher specific power output (horse power per pound) than the equivalent German engine. It was felt that this gave a higher power to weight ratio for the fighter and (rightly or wrongly) that this outweighed the disadvantages. By 1941 Miss Tilly Shilling in Farnborough had developed a partial cure for the problem. A diaphragm across the float chambers with a calibrated hole (the infamous "Miss Shilling's orifice"! I think 'restrictor' is the correct term, orifice sounds like someone's rude sense of humour.) allowed negative 'g' manoeuvres, and was fitted as standard from March 1941. Fitting the new carburettor to the Merlin 45 created the Merlin 50 series. Late production Mk Vs were fitted with the Merlin 50 or 50A and 56 optimised for high altitude, or the 55 with a two-piece engine block. To optimise low-altitude performance the blades of the supercharger blowers were cropped. These engines were identified with the suffix M. For the Mk V these comprised the 45M, 50M and 55M. Sustained zero 'g' manoeuvres were not sorted out until somewhat later. In 1942 an anti-g version of the SU carburettor was fitted to single and two stage Merlins. 1943 saw the introduction of the Bendix-Stromburg carburettor which injected fuel at 5psi through a nozzle direct into the supercharger and was fitted to the Merlin 66, 70, 76, 77, and 85. The final development was the SU injection carburettor which injected fuel into the supercharger using a fuel pump driven as a function of crankshaft speed and engine pressures, which was fitted to the 100 series Merlins.