Honda 400EX Review, Top Speed & Specs

Back in 1998, the sport ATV scene received a jolt of energy with the arrival of the Honda 400EX. The roar of its triumph at the ’98 Baja 1000 announced its presence, and this powerhouse continued its impressive run until 2008. Often hailed as the spark that reignited the sport ATV industry, the 400EX ushered in the era of four-stroke engines and laid the groundwork for subsequent models like the Honda 450R. 

With its sleek and aerodynamic body design, a formidable 397-cc four-stroke engine, aggressive all-terrain tires, and a suspension system engineered for smooth rides across diverse landscapes, the Honda 400EX earned its reputation as an unrivaled trail riding companion. 

Honda 400EX

This article is your guide through the model’s virtues and drawbacks, the secrets behind its top speed, a detailed look at its specifications, and the key features that make it stand out.

Specifications and Features

Engine

The Engine Under the hood of the Honda 400EX rests a robust four-stroke, air-cooled engine with a displacement of 397 cc. This powerhouse produces a potent output of around 28 horsepower. Guided by a 38 mm Keihin carburetor, the engine orchestrates the fusion of air and fuel within a radial four-valve combustion chamber. Demonstrating remarkable low-end torque, this engine effortlessly navigates wooded terrains, trails, and desert expanses. 

While its high RPM horsepower might leave speed enthusiasts yearning for more, the 400EX truly shines on the trail. Notably, its hardiness mirrors that of the Honda 300EX, necessitating regular upkeep in the form of oil changes and valve clearance adjustments to ensure enduring performance.

SpecificationDetails
Engine TypeFour-Stroke SOHC, Gas
Displacement397 cc
HorsepowerApprox. 28 HP
Bore x Stroke Ratio74 x 66 mm
Compression Ratio9.1:1
Carburetion SystemKeihin 38 mm Carburetor w/ Accelerator Pump
Fuel Capacity2.64 Gallons
Starter TypeElectric
Ignition SystemCDI with Electronic Advance
Battery12V 8Ah
Spark PlugDPR8Z (NGK)X24GPR-U (DENSO)

Drivetrain 

The heart of the Honda 400EX’s power lies in its chain-driven system, propelling two wheels into action. A five-speed transmission bridges the connection between the axle and the chain, channeling power to the rear wheels. Models preceding 2005 were devoid of a Reverse feature, which became a standard offering from 2005 onwards. Honda’s ingenious chain adjuster eliminates alignment concerns, guarding against premature chain and sprocket wear.

SpecificationDetails
Drive SystemChain Drive, O-Ring
Transmission TypeManual

Tires & Brake

The Honda 400EX dons 22-inch Ohtsu stock tires at the front and 20-inch counterparts at the rear. The knobby design of these radial tires ensures robust grip, a quality that prompted several riders to opt for the upgrade to Maxxis Razr or ITP Holeshot XC/XCT tires. 

When it comes to stopping power, the dual single-piston hydraulic front brakes and the single-piston hydraulic rear brake shine. This braking configuration guarantees remarkable stopping power even on wet or challenging terrains.

SpecificationDetails
Front Tires22 x 7-10
Rear Tires20 x 10-9
Recommended Tire PressureFront – 4.0 psi Rear – 4.0 psi
WheelsAluminium
Front Brake TypeDual Hydraulic Disc
Rear Brake TypeHydraulic Disc

Suspension System

The Honda 400EX boasts a double wishbone front suspension and a Pro-Link swing arm rear suspension. The Showa shocks, known for their excellence in shock absorption, guarantee smooth rides even on bumpy trails. With preload adjustability, riders can elevate the standard 4.3-inch ground clearance, a feature highly prized for optimizing performance. The suspension configuration provides an 8.2-inch front travel and a 9.1-inch rear travel, ensuring landings after jumps are gentle and controlled.

SpecificationDetails
Front SuspensionIndependent Double-A Wishbone w/ Preload Adjustable Dual Showa Shocks
Rear SuspensionPro-Link Swing Arm w/ Preload Adjustable Single Showa Shock
Wheelbase48.4 inches
Ground Clearance4.3 inches
Turning Radius10.5 feet

Dimensions 

Compact and agile, the Honda 400EX exhibits dimensions of 72.2 inches in length, 45.3 inches in width, and 43.7 inches in height. With a dry weight of 375 lbs, maneuvering this model feels effortless, promising a light touch and seamless control.

SpecificationDetails
Length72.2 inches
Width45.3 inches
Height43.7 inches
Seat Height31.9 inches
Dry Weight375 lbs.

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Honda 400EX Top Speed

The Honda 400EX achieves a top speed of approximately 65 to 68 mph in its stock configuration. Enthusiasts seeking more speed have ventured into modifications, pushing the top speed beyond 70 mph. 

Factors like upgrading the air intake system, and exhaust system, rejetting the carburetor, optimizing tire pressure, using high-octane fuel, and maintaining a healthy spark plug can contribute to increased top speed. However, individual results may vary based on the ATV’s condition and modifications.

Handling

Renowned for exceptional handling, the Honda 400EX shines on tight trails. It offers impressive low-end acceleration, responsive throttle, and user-friendly manual clutch operation. While the lower gear ratio is advantageous for trail riding, it impacts top speed. 

The model handles well in the first three gears, offering stability during cornering and balance during wheelies. However, it might exhibit twitchiness in the handlebars if encountering uneven terrain with a single tire. Riding in soft, steep terrains like sand dunes could pose challenges.

Effective Ways To Increase The Top Speed 

Here are some effective ways to increase the top speed of your Honda 400EX, providing you with comprehensive insights into each method:

Air Intake Enhancement

Upgrading the air intake system can unleash the untapped potential of your ATV’s engine. By replacing the stock air filter with a high-performance alternative like a K&N or Uni filter, you’re allowing a greater volume of clean air to flow into the engine. This results in improved combustion efficiency and increased power output. The increased air intake also enhances throttle response, allowing your ATV to accelerate more quickly and reach higher speeds.

Exhaust System Upgrade

A performance exhaust system plays a pivotal role in optimizing engine performance. When exhaust gases flow more smoothly out of the engine, it reduces backpressure, allowing the engine to “breathe” better. 

This, in turn, leads to increased horsepower and torque, resulting in improved acceleration and higher top speeds. Brands like HMF Racing and Sparks Racing offer exhaust systems engineered for enhanced performance, giving your 400EX an extra edge.

Carburetor Rejetting

Adjusting the fuel-to-air ratio is essential when you modify the air intake and exhaust systems. Rejetting the carburetor involves replacing the jets with larger ones to accommodate the increased airflow. 

This ensures that the engine receives the correct amount of fuel to maintain the optimal air-fuel mixture. A properly rejetted carburetor prevents lean conditions, which can damage the engine, and allows your ATV to fully harness the power generated from the modifications.

Tire Upgrade

Changing your stock tires for larger-diameter ones can have a noticeable impact on your top speed. Larger tires cover more ground with each rotation, effectively increasing the distance traveled per engine cycle. 

This translates to higher speeds for the same engine RPM. It’s important to note that while larger tires can improve top speed, they might slightly affect low-end torque and acceleration due to the added rotational mass.

Optimal Tire Pressure

Tire pressure might seem like a minor detail, but it significantly influences your ATV’s performance. Keeping your tires inflated to the manufacturer-recommended PSI reduces rolling resistance, allowing your ATV to glide more smoothly. 

This reduction in friction enhances acceleration and contributes to a higher top speed. Regularly check and maintain proper tire pressure for consistent performance gains.

High-Octane Fuel

Fuel quality matters when seeking better performance. High-octane gasoline, such as 91 or 93 octane, has a higher resistance to detonation (knocking). This allows your engine to run more efficiently and ignite the air-fuel mixture at the optimal time. The result is smoother combustion, increased power, and improved top speed. Ensure your ATV’s engine is compatible with high-octane fuel before making the switch.

Ignition Timing Adjustment

Tweaking the ignition timing can unlock additional power and speed. Advancing the ignition timing allows the spark plug to ignite the air-fuel mixture slightly earlier in the combustion cycle. This can optimize power delivery and increase top speed. However, this modification requires precise tuning to prevent engine damage, so consult a professional mechanic or tuner to ensure safe and effective adjustments.

Lightweight Parts

Shedding excess weight can significantly impact acceleration and top speed. Replace heavy components with lightweight alternatives, such as carbon fiber handlebars, aluminum wheels, or titanium exhaust parts. These modifications reduce the overall weight of the ATV, allowing it to accelerate more swiftly and achieve higher speeds.

Performance Camshaft

Upgrading to a performance camshaft can optimize valve timing, resulting in increased airflow and enhanced power. The improved valve lift and duration lead to improved combustion efficiency and greater power output. However, installing a performance camshaft is a complex modification that may require professional installation and tuning to ensure proper engine function.

Professional Tuning

When pursuing multiple modifications, professional tuning is essential. A skilled tuner can fine-tune various components, such as the carburetor, ignition system, and fuel delivery, to work harmoniously and maximize power and speed gains. Tuners utilize specialized equipment and expertise to achieve the best results while maintaining engine reliability.

Models & Changes

The Honda 400EX saw numerous models during its production from 1998 to 2008. While early models remained relatively consistent, the 2005 model introduced significant changes such as updated bodywork, suspension enhancements, and the incorporation of a Reverse gear. The final 2008 model featured modern bodywork and plastics, serving as a fitting farewell to its production run.

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Honda 400EX Price:

Curious about the historical pricing of the Honda 400EX? Take a look at the initial list prices for new models and the current average retail prices for used models by year.

Year, Make & ModelList PriceAverage Retail Price
1999 Honda 400EX$5,499$1,265
2000 Honda 400EX$5,699$1,425
2001 Honda 400EX$5,699$1,615
2002 Honda 400EX$5,699$1,815
2003 Honda 400EX$5,699$2,035
2004 Honda 400EX$5,699$2,165
2005 Honda 400EX$5,799$2,295
2006 Honda 400EX$5,899$2,430
2007 Honda 400EX$5,999$2,595
2008 Honda 400EX$5,999$2,785

The Honda 400EX retains its well-deserved respect and popularity even years later within the off-roading community. This enduring popularity has contributed to its sustained value over time. When perusing the used ATV market, you’ll likely find listings ranging between $2,000 and $4,000, with the exact price contingent on factors such as the model year and the overall condition of the ATV.

Notably, the 400EX’s reputation for reliability and the availability of affordable aftermarket parts make it an appealing option for enthusiasts considering a used ATV. Its enduring value and timeless appeal are a testament to its status as a cherished classic within the world of sports ATVs.

Pros & Cons

Pros

  • Engine durability with minimal mechanical flaws.
  • Reverse gear (2005+) aids in trail riding and maneuvering.
  • Compact size facilitates transport and storage.
  • Outstanding handling for trail riding.
  • Balanced wheelies and excellent stability.
  • Honda’s reputation for reliability.
  • Availability of affordable aftermarket parts.

Cons

  • Wiring harness wear in early models may lead to shorts.
  • Factory front shocks could be improved for optimal suspension performance.
  • Non-replaceable rear grab bar due to subframe integration.
  • A ticking sound could indicate valve and timing chain maintenance.
  • Swing-arms susceptible to cracking during hard landings.
  • Modest power and speed on flat surfaces.

Comparable ATVs

Several ATVs bear resemblance to the Honda 400EX in terms of features and performance. These include the Yamaha Banshee 350, Yamaha Raptor 350, and Honda 300EX. A comparison of key features provides insights into their similarities and differences.

FeatureYamaha Banshee 350Yamaha Raptor 350Honda 300EX
Engine Displacement347 cc349 cc282 cc
Stock Horsepower34 hp22 hp21 hp
Top Speed75 mph63 mph58 mph
Ground Clearance5.3 inches4.5 inches4.9 inches
Dimensions (L x W x H)75 x 41 x 42 inches70 x 43 x 42 inches68 x 43 x 42 inches

FAQs Section

Can I increase the top speed of my Honda 400EX without modifications? 

While slight adjustments to tire pressure or upgrading to premium fuel might yield marginal improvements, significant increases in top speed typically require modifications to the ATV’s engine, intake, exhaust, and other components.

Are aftermarket parts necessary for increasing top speed? 

Aftermarket parts, such as performance air filters, exhaust systems, and carburetor jets, can greatly enhance top speed. These components are designed to optimize airflow, combustion, and power delivery, resulting in substantial speed gains.

Will modifying my ATV affect its reliability? 

Any modification carries the potential to impact reliability. It’s crucial to strike a balance between performance gains and the longevity of your ATV. Professional installation, proper tuning, and regular maintenance are key to ensuring both increased speed and long-term durability.

Can I install these modifications myself? 

Some modifications, like adjusting tire pressure, you can handle on your own. However, more intricate modifications, such as rejecting the carburetor or installing a performance camshaft, are best left to professionals with the expertise and tools to ensure proper installation and tuning.

Will increasing the top speed affect other aspects of performance? 

Modifications that enhance top speed, such as larger tires, may impact other aspects of performance, such as low-end torque and acceleration. Striking a balance between various performance parameters is crucial to achieving a well-rounded ATV experience.

How can I ensure the safety of my ATV after modifications? 

Prioritise safety by working with experienced mechanics or tuning professionals who specialize in ATVs. They can provide expert guidance on modifications, ensure proper installation, and conduct thorough testing to verify that your ATV remains safe and reliable after enhancements.

Final Verdicts

In the world of sports ATVs, the Honda 400EX stands as a trailblazer of exceptional performance and enduring legacy. From its debut in 1998 to its final production year in 2008, the 400EX has left an indelible mark on the off-road landscape. Its remarkable specifications, remarkable top speed, and unwavering reliability continue to resonate with riders seeking the thrill of speed and the joy of exploration.

With each twist of the throttle, the Honda 400EX encapsulates the essence of adventure and the pursuit of speed. As you navigate rugged trails and seek the next adrenaline rush, the 400EX remains a steadfast companion, inviting you to embrace the open terrain and experience the boundless freedom of off-road riding.

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