Spit IIa is now so much more inferior to the 109

[TomcatViP]

it has more to do with the airstream ard the prop, hence the aircraft speed in that case (fixed pitch).

Max rpm is more a function of admissible eng wear. It always a trick for eng manufacturer to increase rpm to raise the number of HP available.

I think tht latter in the war, the Merlin's limits were raised to 3k rpm [confirmed - see above].

There is nothing hidden here: just like you ride your bicycle, you can't reach your max rpm at high gear starting from rest.

The Hurri had a thicker wing, so it didn't need so much speed at T.O as the Spit. Hence the T.O pitch setting wldn't need to be as lean as tht one for the spit. If the Merlin was tuned for both aircraft, it wld seems normal tht the max admissible rpm for the Merlin wld hve been fixed as a ref for the Spit and then wld hve differed slightly with the Hurri.

This are only supposition. Take it only as it shld be.