Before tail pipe emissions testing, mpg were very high. Thanks EPA.

https://www.ericpetersautos.com/2015/08/19/crippling-technology/ >Here we are – almost 2016 – and the typical new car is about as economical to drive as the typical car of 1985. This is hard to believe, but you should believe it because it’s true. The typical car of the early-mid-1980s was averaging mid-high 20s – just like today. There were numerous models available that approached or even exceeded 40 MPG on the highway. A few (like the diesel-powered VW Rabbit) got into the 50s. >They did this without direct-injection or even port fuel-injection. Many still had carburetors. Eight and nine-speed transmissions (with the top three gears being overdrives) were unheard of. Most automatics of this era had four speeds. Some still had just three. >But the one thing the cars of that era did have was less weight – about 500-800 pounds less of it, on average, than comparable cars have today. And the sole and only reason for all this additional weight is the increased demand for “safety” eructing from the solons in Washington. Well, so we must presume. Because the people who actually buy the cars were never offered the free choice. It would be interesting to find out what they’d choose if they did have that choice. https://www.ericpetersautos.com/2022/10/01/they-dont-just-look-the-same/ https://www.ericpetersautos.com/2018/10/14/less-gas-in-your-gas/ https://www.ericpetersautos.com/2017/08/09/four-wheeled-diversity/

Yeah, the original civics got high mileage. Then regulations started hitting and you couldn't build cars like that anymore. Subaru's first car in the USA was a tiny little box that did similar.