P-39D
Allison V-1710-35 (E4) engine

P-40E & Mustang Mk1
Allison V-1710-39 (F3R) engine

P-38F
Allison V-1710-49/53 (F5) engine

P-38G
Allison V-1710-51/55 (F10) engine. Increased boost ratings, however, the engine was HP limited due to inadequate intercooler / cooling. A problem that was only fixed with the P38-J!


Regarding Higher Boosts
Something that I did find in the Mustang MK1 pilot notes is that a higher boost is allowed but when the plane is fitted with an automatic boost control and special spark plugs!

This document informs how the British removed the automatic boost control in order to overboost them even higher than 56"
http://www.wwiiaircraftperformance.org/ ... eh-16.html



It wasn't until December 1942 that WER ratings were increased on the Allison V-1710-39.
It was cleared to use of up to 56" Hg as a war emergency rating for duration of 5 minutes.

Note: The Allison engine was cleared for 56", it doesn't necessarily mean it was automatically used!

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