More like 99 percent of the fuel burns completely, with the cat taking care of the rest. Maybe he meant 25 percent thermal efficiency, which is close to being correct. The problem is that the theoretical maximum is only about 35 percent for an otto cycle internal combustion engine.

A five minute test at 80mpg proves nothing. I once got 100mpg (as shown on the trip computer) in a rented Cadillac, coasting downhill.