I went thru the JC Whitney catalog once and bot everything that would enhance gasoline economy.
I had to stop tho.
When I got to the point where my car was making gas, I had nowhere to store the excess.
I also had a (calculated) 1300 HP at the rear wheels.
Not bad for a Miata.
Eventually Mazda bot the car back and it is now in an Automotive Museum next to the Fish Carbuerator (1950s carb that got any car 100MPG. The Fish Carb was donated by a major oil company who had bot the patent and the carb from the original inventer)