Hi Dieter, gang, 8 mpg sounds a little low, but there are so many variables to take into consideration and I don't know anything about the 331. If it is any help to you as a single data point, here is my situation. '62 413 with a burnt #7 exhaust valve. 4 barrel Carter AFB. No special mods from what was offered in '62 for the Imperials with the exception being a Mopar performance electronic ignition. Single exhaust. Low and uneven compression on the remaining 7 cylinders. She rolled her odometer 3 days ago on the original engine and transmission. 200K possibly 300K miles. Other than the burnt valve, I keep the engine in good tune. (plugs, wires, fluids, etc.) I have 235 75 15 radials all around. This 413 gets 11 mpg around town, and up to 15 mpg on the highway. Hope this helps. Imperial Regards to all, Jay Mc Kee '62 Crown Four-Door Southampton http://klia.net/jay/