What advantage did fuel injection give the Bf 109?

In a fuel-injected engine, a measured dose of fuel was injected directly into each cylinder, eliminating the carburetor. The Daimler-Benz DB 601, an inverted V12, used fuel injection from 1937.

This gave 109 pilots a combat advantage: they could perform negative-"g" maneuvers without the engine failing. A Messerschmitt pilot could dive into a descent that a Spitfire or Hurricane pilot could not follow without losing vital moments of engine power. German pilots exploited this by sharply pushing the nose down while opening the throttle, a maneuver that the British aircraft chasing them could not copy. German fighters with direct gasoline-injection engines did not suffer this problem, because the injection pumps kept the fuel at constant pressure.

Shilling designed a thimble-shaped brass flow restrictor, with dimensions precisely calculated to let through just enough fuel for the engine's maximum power. Without fully solving the problem, the restrictor, together with modifications to the needle valve, allowed pilots to perform quick negative-"g" maneuvers without losing power. This improvement resolved the disadvantage of RAF fighters powered by the Rolls-Royce Merlin against the Messerschmitt Bf 109 E. In early 1941, Shilling traveled with a small team to fit the restrictors at one RAF base after another, prioritizing front-line units. By March 1941 the device was installed throughout Fighter Command.