In article , MVP writes
During the Mobil Economy runs, I think they used to do Lands End to John'o'Groats if my memory serves me? They used to get remarkable mpg's such as 50 mpg from things like Zephyr 6's (6 cylinder 2.6 litre cars that typically returned about 26 mpg) with a crew of two and lots of interesting non standard gauges and controls that would have included a vacuum gauge.
Essentially it was just about driving with the utmost care to minimise sucking fuel, such as avoiding braking and accelerating! Using motion inertia by finding that perfect balance between momentum and throttle, ensuring the vehicle is tuned and as smooth running as possible, tyres at optimum inflation. The vacuum gauge was the crucial fuel flow indicator in those carburettor days. I fitted one to a Ford Corsair GT in 1967 and wondered at the huge change in fuel flow that could be made by the smallest change in throttle without noticeable difference to speed. Using such driving techniques I once returned 56 mpg, two up with luggage, from London to Poole in a 14 year old Morris 1000 at reasonable cruising speeds (speedo indicated 70 on the M3)