This article is from the The Monster Truck FAQ, by Jeff Hawkins with numerous contributions by others.
A. Racing Alcohol is the fuel of choice for most monster trucks. It
runs cooler while producing more horsepower. Nitrous oxide is NOT
allowed by the Monster Truck Racing Association and a monster
truck won't pass Tech. Inspection and will not be certified to
race with an engine injected on it.
Most of these trucks use a little gasoline to start the engine,
either squirting it in by hand through the Blower air intake or
using a auxiliary fuel pump to inject a small amount to the intake