In stock form, the Honda TRX400EX typically produces about 28 to 30 horsepower at the crank, depending on the year and tuning.
The 400EX is a 397cc, air- and oil-cooled four-stroke ATV produced by Honda from 1999 to 2008, known for its balance of power and handling. Power ratings can vary by source and measurement method, but the prevailing figure sits in the high-20s horsepower range.
Engine power basics
Horsepower figures for ATVs are usually quoted as brake (crank) horsepower at the engine, before drivetrain losses. The 400EX uses a single overhead cam (SOHC) four-stroke layout with carburetion, and its power output was tuned for reliable midrange torque as much as for peak horsepower.
Model-year horsepower snapshots
For quick reference, here are commonly cited stock horsepower estimates by production window. Numbers vary by source and measurement method.
- 1999–2004 TRX400EX: typically around 28 hp at the crank, with some sources listing 27–29 hp depending on calibration and measurement.
- 2005–2008 TRX400EX: commonly cited around 28–30 hp at the crank, with minor year-to-year variation.
Across the production run, the horsepower remained in the high-20s, with the exact figure depending on model year, altitude, temperature, fuel quality, and whether the engine was stock or tuned.
Notes on measurement and practical use
Horsepower is only part of the performance picture. Real-world speed and acceleration also depend on weight, gearing, tires, and the condition of the drivetrain. If you’re comparing to modern ATVs, the 400EX’s horsepower is modest by today’s 450cc-class standards, but its overall package—handling, reliability, and ease of maintenance—kept it competitive in its era.
Summary
The Honda TRX400EX typically delivers about 28–30 horsepower in stock form, with the exact figure varying by model year and measurement method. For buyers or restorers, identifying the specific year and confirming any modifications is key to estimating current power. Overall, the 400EX sits in the high-20s horsepower range and remains a notable part of ATV history for its blend of performance and practicality.