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Originally Posted by kachok25
LOL NO I think you are way off on that one, the octaine has nothing to do with BTU rating. Octaine is just a mesurment of a type of molicule in the gas, that takes a little longer to burn because it is such a long chain of hydrocarbons.
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Actually he is spot on. The additives that go into gasoline (which we falsely call octane) have much fewer BTUs than gasoline. The net result is a lower BTU content of the fuel, but not by much.
Gasoline has a BTU content of about 18,400 per pound. Methanol is about 9500/lb. Nitromethane is 5000/lb, so actually nitromethane has about 70% less energy than gasoline.
But, Gasoline is typically burned at 12.8:1 for most power. Methanol is mixed at about 6.0:1 and Nitromethane a staggering 1.7:1.
All things "equal" using some equations I did for another project that used 567cfm, it works out like this at 6500 RPMs: A gasoline engine would have 53,176 BTUs released, a Methanol engine would have 67,545, and the Nitro engine would have 125,412 released.
Octane is an actual hydrocarbon; C
8H18 like its kins, propane, heptane, butane, etc. Octane is very hydrophillic so fuel systems don't use it anymore. It used to be standard fare, but the fact that its highly volatile, has a high vapor pressure, and was determined to be a deadly carcinogen caused the switch to tetraethyl lead. Now we use other additives to achieve the octane rating which is an estimation of its knock preventative abilities. Its called the octane rating because of the namesake of the chemical it replaced.