"M. H. Greaves" wrote in message
...
Cant remeber exactly but werent the allison engines unsuitable because
they
were no good above a certain altitude!?

Depends on which Allison engines

When fitted with a turbo supercharger as in the P-38
they were fine, with a less capable blower setup
as used in the P-40 they were less good but then thats
tue of various marques or Merlin too.

Keith