There was a guy in the 1970s during the oil embargo that figured out you can run a V8 on literal gas fumes and get 100mpg. He drove about 200 miles to prove it. Car companies studied the car. It was true, but the car had no power; like 0 to 60 in a minute or something. It was bad for the engine, it needed a system that heated the gas and pressurized it, over complicated and basically a bomb under the car. The conspiracy is the car companies just agreed not to make it in a backroom deal with OPEC.