A stock TRX400EX typically makes around 30 horsepower at the engine crank.
The Honda TRX400EX is a 397cc four-stroke ATV produced from 2004 to 2008. Its horsepower varies by year, dyno method, and condition, but stock figures generally sit in the low-to-mid 30s horsepower range on crank measurements. Real-world wheel horsepower will be lower due to drivetrain losses and gearing.
Stock horsepower by year (approximate)
Below are approximate stock horsepower figures reported for the TRX400EX across its production years. Values refer to engine crank horsepower as measured on dynos and can vary with fuel, exhaust, altitude, and wear.
- 2004–2005 TRX400EX: about 32 HP (crank)
- 2006–2008 TRX400EX: about 30–31 HP (crank)
In practice, stock horsepower tends to hover in the low- to mid-30s for early models and settle around 30 HP for later years, with modest gains possible from exhaust or intake upgrades.
Factors that can affect horsepower
The horsepower figure on a TRX400EX is not fixed. It depends on multiple variables, including engine wear, altitude, temperature, fuel quality, and any modifications. The following factors commonly influence measured output:
- Engine condition and maintenance (compression, valve clearance, and timing)
- Altitude and temperature (air density affects power)
- Fuel octane and tuning (jetting and fuel delivery for carbureted engines)
- Intake and exhaust modifications (air intake, muffler, and exhaust flow)
- Drivetrain and gearing (affecting rear-wheel horsepower versus crank horsepower)
With proper maintenance and modest upgrades, owners often see small increases in peak horsepower, though wheel horsepower typically rises less than crank horsepower due to drivetrain losses.
Practical notes for enthusiasts
For those evaluating a used TRX400EX or planning a build, dyno testing is the most reliable way to quantify horsepower. Factory ratings aren’t consistently published by Honda and can vary by testing method and market. Always compare crank horsepower to wheel horsepower and consider torque, gearing, and riding conditions in addition to peak numbers.
Summary
The TRX400EX generally delivers about 30–32 HP at the crank in stock form, with modest year-to-year variation. While official, standardized horsepower figures from Honda aren’t uniformly published, dyno results and reputable sources tend to place the stock output in the low-to-mid 30s range. Upgrades can push the number higher, but real-world performance also hinges on torque, gearing, and how the ATV is ridden.