BLUF

Changing to 100-octane (100/130 aviation gasoline) just before the Battle of Britain increased the speed of the Spitfire by 25-30 M.P.H. at low and medium altitudes and made it equal, or superior, to the German Me 109 at all altitudes.

Summary

Richard Dunn writing in Warbird Forum, makes the following points:
  • In the early 1930s, motor fuel rated about 40 octane, aviation fuel 70-80.
  • Aviation gasoline comprised about .5 per cent of the market.
  • Aviation pioneer Jimmy Doolittle (later famous for the WW2 Doolittle Raid) lobbied Shell and the government to increase 100-octane production to make it cheaper through economies of scale.
  • In 1937 the US Army (for the Air Corps) mandated 100-octane for combat aircraft.
  • After some hesitation, the RAF modified the Merlin engines of Spitfires and Hurricanes to 100 octane before the Battle of Britain.
Learn more about the importance of high octane during the Battle of Britain.

References