3rd Oct 2019, 21:19

Emissions was the reason VW stopped production of the air-cooled engines, as did Porsche. Even motorcycles gave moved away from air-cooled. Given the wide temperature range an air-cooled engine runs at, it requires much greater, or looser tolerances than a liquid cooled engines, which means more blow by or siphoning of oil past the piston rings or cylinder walls to start with, which permits oil to be burned in the combustion chamber, raising the emissions tremendously. This also leads to shorter engine life. On a plus side, they're easy and cheap to build with average MPG, but air-cooling limits the the RPM, power output, and general quality and longevity.