sycamore,
Thanks. I'll have to look for that book. A good book that has a lot of Merlin information, particularly concerning superchargers, is Stanley Hooker's autobiography "Not Much of an Engineer".
There is a lovely anecdote in it, which I am paraphrasing from memory, where Stanley Hooker told Lord Hives that the full-throttle height of a new prototype supercharger would be about 30,000 feet. After a flight test, Lord Hives passes over a piece of paper with one number on it - 29,000+ feet.