Friday Update, February 10, 2012

[Robo.]

Originally Posted by 41Sqn_Banks

I have the Merlin III engine manual (AP 1590B) updated for the use of 100 octane fuel. Amendment List No. 4 to AIR PUBLICATION 1590B includes a completely new page with "Performance" and "Limiting operational conditions" that is dated November, 1940 and gives nominal ratings with +6.25 lb. per sq. in.
I'm confident that these new pages from November 1940 wouldn't state outdated values. So I'm convinced that there was no rated power of +9 lb. per sq. in. on a regular Merlin III engine (without modifications to bring it to Merlin XII standard).

The infamous +9 boost document is useless without knowing the source. It is Page 40 of a larger document. At least we need to have the other pages to bring it into the correct context. It even could be a typo (III instead of XII).

In R.M.2.S. nomenclature it says +8.25lbs as a take-off rating (one minute), but just as you say, nominal ratings were never +9lbs for Merlin III.