Not sure if its a thing that is done/used in the US but here in the UK It is something that is commonly carried out to large engined motors and thats to LPG the vehicle, thats where the petrol fuel system is supplemented with a Liquid Petroleum Gas set up with 8 injectors mounted and a piggy back ECU that runs them and cuts the petrol out and runs solely on LPG and if the system is fitted by a reputable company you lose no performance and the only thing that comes out the exhaust is water vapor so its a super clean burn my oil changes (every 6k) the oil comes out as clean as when I put it it and thats no exaggeration.

I get around 18-19mpg with spirited driving but with the cost of LPG half the cost of petrol you are achieving a cost comparison mpg of 35-37mpg that makes running a big V8 cheaper than a 4cyl BMW sedan.