Spit IIa is now so much more inferior to the 109

[Crumpp]

There is no documented use of the original boost cutout as a combat boost system I am aware of, but it would be possible. The pilot would need to be very careful not to exceed a boost level that caused predetonation or engine damage, and the boost would continuously change with rpm, height and throttle position.

That document giving 10.55 psi boost is very interesting. As Banks suggested, it appears to be the boost attained with full throttle and (unmodified) boost cutout pulled at height. The height is about right. Interesting in that such a high boost was usable at all in a Merlin III on 87 octane.

However it is very unlikely that pilots were ever authorized to use the unmodified boost cutout as emergency power because the risk of instant degradation of engine performance was high (especially at low altitudes)

I agree that specific authorization was probably not given and the risk was high.

The RAF pilots were given license to use it in the General Operating Notes. The Air Ministry openend the door and I am sure pilots died as a result.

They were instructed to balance the risk. Given the fact these guys were not the technically savvy pilots we see today, it makes sense you would have a high incidence of those who thought they knew better with such instructions.

Defining that point of balance was obviously an issue for the RAF as several memo's appear at various times during the war warning of the dangers of over boosted conditions.