From the Dresserator carburetor to magic polymerizers to magnets on fuel lines, all kinds of devices have been introduced. Their main claim to success has been in separating their customers from their money.

Carl Dresser (if memory serves) introduced his carb in the late 60s/early 70s and did manage to get Ford to look at it. They never committed obviously. Several car enthusiast magazines tried for some time to get access for evaluation purposes. Popular Mechanics I think it was finally got access around 1980 or so with very unsatisfactory results.

They installed one on several different engines and even after extensive tuning achieved negative results. In most cases mileage actually worsened with the miracle carb. This is the carb that popular mythology says 'was bought out by the oil industry' lol.

The auto companies have had incentive to do the best they can ala fuel mileage, most especially since the EPA and CAFE regs starting affecting business. I would hate to venture a guess as to just how much money has been thrown at it, billions surely.

New engines, intake and exhaust system design, combustion chamber design, fuel composition, you name it. Roller bearings in the valve train, 4 valve heads, computer controlled fuel injection with exhaust feedback, improvements to coefficient of drag, rolling resistance, weight savings with novel materials, all kinds of advances have been made.

There is no lack of trying in the industry to achieve the best possible fuel mileage. The basic formula hasn't changed a lot though in the last half century. A 3200 lb. car with a small block V8 in 1967 could reach 25 mpg on the highway if driven correctly. A new Corvette weighs roughly the same, has much better aero and can do only slightly better, rated at 29 mpg highway, probably more realistically 25 to 27.

We're up against physical limits here it would seem. Cut the weight drastically with much smaller cars, go bonkers on rolling resistance, aero and engine size and then teach people how to drive for mileage. Instant 50+ mpg.

All kinds of things out there to separate you from your money. Until outfits like this one come clean with details I remain skeptical.