In our everquest for more power we need consider what propels our cars, FUEL. Most hot rodders usually only consider running one type of fuel in their engine, gasoline.
This article's intent is to explore some of the other alternative fuels, alcohol, and nitromethane.
Gasoline is what most of our cars came setup so it's usually what we stick with. Gasoline is a mixture of hydrocarbons. The petroleum distillate fraction termed "gasoline" contains mostly saturated hydrocarbons usually with a chemical formula of C8H18. The air fuel ratio, A/F Ratio, for complete combustion is 14.7:1, stoichiometric. The A/F ratio for maximum power is approximately 12.5:1 - 12.8:1. This means that our engine at max power, 12.8:1, consumes 12.8 pounds of air for 1 pound of fuel. Gasoline has approximately 18,400 BTU/lb . Using the air flow calculator with the default inputs we get our 355 SBC consumes 567.53 cfm @ 6500rpm which is 42.64 pounds of air and consumes 3.33 pounds of fuel. Therefore if we are using gasoline our engine is producing 61,295 BTU's of energy at 6500 rpm.
Alcohol (Methanol) -
Alcohol is usually used in the form of Methyl alcohol or methanol. CH3OH is the chemical formula. Methanol burns at a much richer mixture than gasoline does, between 5.0:1 - 6.0:1. That's 5 lbs of air to one pound of fuel. Methanol has approximately 9,500 BTU/lb. Using our 355, example above, SBC consumes 567.53 cfm @ 6500rpm which is 42.64 pounds of air and now at 6.0:1 ratio for Methanol is 7.11 pounds of fuel. Therefore if we are using Methanol fuel our engine is producing 67,545 BTU's of energy at 6500 rpm.
Nitromethane - is a fuel that is used mostly in specialized drag racing classes, "nitro funny cars" and "top fuel". Nitromethane's chemical formula is CH3NO2. The oxygen in nitromethane's molecular structure means that nitromethane does not need as much atmospheric oxygen to burn, part of the oxygen needed to burn nitromethane is carried in the fuel itself. Typical A/F ratio for nitromethane is 1.7:1 and nitromethane has an energy content of 5,000 BTU/lb. Using our 355, example above, SBC consumes 567.53 cfm @ 6500rpm which is 42.64 pounds of air and now at 1.7:1 ratio for nitromethane is 25.08 pounds of fuel. Therefore if we are using Nitromethane fuel our engine is producing 125,412 BTU's of energy at 6500 rpm.
||Engine Air Flow (cfm)
||lbs of air (lbs)
||Pounds of Fuel (lbs)
||Energy Content of Fuel (BTU/lb)
||Total Thermal Energy (BTU)
Summary - As you can see from table 1 above the clear winner is nitromethane. But that doesn't mean to go out and pour nitromethane in your car and see how it runs, if you do your engine will surely blow up. Nitromethane is very expensive and dangerous to handle. The interesting alternative to gasoline is Methanol. Methanol will make more power, typically around 10% more power than a similar engine running gasoline. Some things to consider in running methanol is your fuel system will have to be completely changed / upgraded. Based on the table above the fuel system will have to flow approximately 2.5 times as much as the gasoline engine.
I guess the old saying is true. "Gasoline is for washing parts, alcohol is for drinking and nitro is for racing."