Many moons ago,---12 mpg from a 1971 Triumph 2.5 PI. The Lucas PI system wa notoriously thrsty, but 12 mpg was well OTT. I bought the 2.5 PI for £25 after someone rear ended my Triumph 2000 ( on Christmas day 1978), and it was cheap because the ends were knocking. Back then, ripping out an engine and getting the crank ground was no big deal and only afterthe rebuild did I discover its inherrant thirst. After further investigation I found that someone in its not so distant past had fitted a TR250 engine. This engine was fitted to the American TR250 Sportscar ( similar to a TR6 ) how this engine made its way into the car I never knew, but it was a twin carburretor engine and never designed to run on petrol injection. So I reppied out the injection system, fitted twin Stronbergs and restored a 25mpg consumption. Also i sold the injection system for more than I paid for the carburretors and inlet manifold so a result all round. I still have the engine lurking about in my garden.