Spit IIa is now so much more inferior to the 109

[NZtyphoon]

Originally Posted by 41Sqn_Banks

It's interesting to note that publications from 1938 and 1939 give maximum take-off engine speed of 2850 rpm for both Merlin II and III. Publications from 1940 give 2850 for Merlin II and 3000 rpm for Merlin III. The increase is not associated with the use of 100 octane fuel.

This most likely has a great deal more to do with the adoption of two speed and CS propellers; in 1938 the majority of the Hurricanes and Spitfires were still using the fixed (coarse) pitch two bladed wooden props, so the maximum allowable rpm was fixed at 2,850.

The Merlin III had the universal prop shaft allowing de Havilland or Rotol propellers to be fitted, and the availability of two-pitch and especially CS props would have allowed for higher rev limits with less strain on the engine than a fixed-pitch unit. It also makes sense that in wartime some restrictions are lifted to allow for maximum power. One of the reasons 100 Octane fuel was originally adopted was to allow greater take-off power.