They probably mean that it's like the stories about 100x battery capacity improvements that end up as a 20% capacity boost in actual products that appear on sto

They probably mean that it's like the stories about 100x battery capacity improvements that end up as a 20% capacity boost in actual products that appear on store shelves. Prototypes are always more impressive than marketable products. In his case, maybe there are acceleration/deceleration issues, maybe the engine would be cost prohibitive for manufacture, or maybe he'll have to modify the vehicle itself to achieve the 100mpg number. The point is that there's likely to be some constraint that makes it impractical. As an extreme example: https://en.wikipedia.org/wiki/Pac-car_II https://en.wikipedia.org/wiki/Pac-car_II There's a reason that we aren't driving hydrogen fuel cell cars with 12,600 MPGe fuel economy.