In case you were still wondering I got a reply from the Blenheim Society on the two fuels in the Blenheim:
...... has passed me your query re fuel of different octane ratings used in the Blenheim IVs. Yes they did have two different fuels in the same aircraft!
100 octane in one pair of tanks used for take-off and emergencies with a 'Plus 9 lbs boost' lever, and a lower octane fuel for far less boost pressure, used for cruising, in another pair, and of course this did lead to many accidents, often fatal.
How this came about is explained in detail in my book "The Bristol Blenheim - a complete history" published by Crecy. You can buy one at the discounted price of under £30 for Blenheim Society members from Ron Scot the Society Hon. Treasurer on 01 992 442 608 or borrow one from a public library.
Seems to me one or more of your group could join the Society at £15pa as they publish an excellent Journal, and have an annual Blenheim Day and lunch at Duxford with access to the actual aircraft and opportunity to meet the few remaining wartime crew and the present day engineers.
Regards Graham Warner
Enthusiasts may like to buy his book and even join their society
