Cub Driver wrote in message . ..
British based Spitfire IX squadrons had converted to 150 octane
(actually 100/150 octane, for lean/rich rating) by, or during, May 44.

Is this the same as 100 octane, then? As used for example in the
Curtiss P-40?

all the best -- Dan Ford
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The common 100 octane fuel had an octane rating of 100/130, which
means 100 in lean mixture, 130 in rich mixture. 150 octane was
actually 100/150. I suppose that means no difference in lean mixture,
but in rich it had a tremendous effect. The Merlin went from 67" to
82", for example (although the USAAF rated them more conservatively,
at 72" iirc)

100/150 wasn't in use until the spring of 1944, although it was being
tested in 1943.