It is like running nitrous through your carbs.
1 lb of gasoline requires 14.7 lbs of air. 1 lb of Nitromethane requires 1.7 lbs of air.
When nitromethane is compress and burnt, it breaks down releasing oxygen. That is why it only requires 1.7 lbs of air compaired to 14.7lbs that gasoline requires.
nitromethane produces 2.3 time more hp than gasoline. I dont know how you would be able to get the carbs to flow enough to run a high percentage of nitromethane.
Most of the time when they run it, it will be mixed with methanol. The top fuel dragsters generally run 90% nitromethane 10% methanol.