Yeah your fuel consumtion will increase, a trade-off for more power. Some things to consider with nitromethane: it does not require as much oxygen as gasoline to combust, so it is in effect, a richer mixture, it burns hotter than gasoline, so its caloric release is greater, it burns faster than gasoline, and it has a lower flash point than gasoline, so it will ignite at a lower temperature. All these reasons are why drag racers love it. The down sides are that it is hideously expensive when compared to gasoline, and has a propensity to blow engines up when too high a percentage is used in a high compression engine. It also, by virtue of some of the characteristics above, has the effect of advancing ignition timing in the engine, which is also responsible for increasing power, and causing detonation. Of course, drag racers use (best I can recall) about 75% nitro, so they're really pushing the envelope. I made the above comparisons to gasoline, but pretty much the same holds true for methanol.