Spit 1a

[ATAG_Dutch]

According to the graph on the link I gave, the Spit1a with +6.25lbs boost should be 285mph @ zero ft, with 355ish @ about 19.000ft. But it does state @ 3000rpm, and with a Rotol prop.

The +12lb graph shows higher performance all round. I couldn't find a two-speed prop performance graph, but will have a hunt around.

Edit: The only reference I could find to DeHavilland 2-speed prop performance was in Alfred Price 'The Spitfire Story', but no figures are present for max speed at sea level. Max @ 18,600ft is 367, ceiling 34,400.

It does state that the original fixed pitch 2-bladed prop had max speed @ 2000ft (lowest shown) of 295mph. The 2-speed prop was much heavier, inhibiting the rate of climb, but you'd expect performance in coarse pitch to be similar to the fixed pitch.