The Honda 400EX is an all-terrain vehicle (ATV) manufactured by Honda Motors Company from 1999 until 2009. It has a four-stroke 397-cc engine with an output of around 28 horsepower. The 400EX has a top speed of 72 MPH. The 400EX is known for its excellent handling, and many riders consider this model one of the best trail riding ATV's ever made.