Me too, It is funny how power/efficiency works to up your mpg at the same time. The 273 and the mpg was a complete surprise. But that was in the 80's in South Dakota where you could cruise in highway mode for hours. The 170 was a lark. I had read about the Baby NASCAR 170's and felt I had to pull 273 because of compression issues. Not as hot as yours, but no one would believe it was a 170. That darned thing would also top 30 mpg in the same car and same set up. I do believe aerodynamics played a roll also, since they were in a 64 Barracuda.