Top 12 Best Big Bore Kit For 400ex That Will Blow Your Mind

Upgrading your Honda 400EX for better performance can be challenging without the right parts. A reliable big bore kit often makes a noticeable difference in power and efficiency. The best big bore kit for 400EX is designed to enhance your engine’s displacement, giving you extra torque and smoother throttle response.

This product is ideal for riders who want to improve their ATV’s performance for trail riding or light racing without complex modifications. Beyond just increasing size, the kit typically includes components that fit well and maintain engine reliability.

This review will cover the key features, compatibility, ease of installation, and what you can realistically expect from the upgrade. By the end, you’ll have a clearer idea of whether this big bore kit suits your Honda 400EX and riding needs.

Unlock Maximum Power and Performance: Top Upgrades for Your 400EX Engine

Image	Product	Price
Our Top Picks 1	PANGOLIN Cylinder Top End Rebuild Kit for Honda TRX400EX	Check Price
Our Top Picks 2	440cc Big Bore Cylinder Piston Ring Kit for Honda TRX400EX/X	Check Price
Our Top Picks 3	89mm 440CC Big Bore Cylinder Piston Gasket Kit for TRX400X	Check Price

1. PANGOLIN Cylinder Top End Rebuild Kit for Honda TRX400EX

Upgrade your Honda TRX400EX with the PANGOLIN Cylinder Top End Rebuild Kit, designed to restore engine performance efficiently. This kit offers a precision-engineered solution tailored specifically for the TRX400EX model, ensuring compatibility and dependable results.

Built with high-grade materials, it delivers durability and stable performance. Experience smooth engine operation with parts crafted for reliability and long service life.

Every component in the PANGOLIN kit is carefully manufactured to match or exceed OEM quality standards. The cylinder features premium cast aluminum construction, while the piston is crafted from robust aluminum, providing both strength and lightweight durability. With an 85mm bore size, it is designed to fit Honda TRX400EX models from 1999 to

With an 85mm bore size, it is designed to fit Honda TRX400EX models from 1999 to

Replacing worn pistons and rings can dramatically enhance engine power and reduce oil consumption. This kit makes maintenance straightforward, supplying all necessary components for a comprehensive top-end rebuild. Users will appreciate the stable characteristics and longevity built into each part.

Users will appreciate the stable characteristics and longevity built into each part.

Ideal for riders aiming to keep their ATVs running smoothly, the kit suits weekend riders and daily users seeking reliable engine performance. Installation is hassle-free for those with basic mechanical experience and comes backed by PANGOLIN’s customer support policy.

Compared to similar kits, this offering strikes a balance between affordability and quality, without compromising on durability.

Pros

• High-grade cast aluminum cylinder and piston for durability
• Complete kit includes piston rings and all top-end components
• Compatible with Honda TRX400EX (1999-2008) models with 85mm bore

Cons

• Installation requires mechanical knowledge or professional assistance

This rebuild kit offers an effective way to restore your ATV’s engine to its intended performance. It combines quality materials and precise engineering, making it a solid choice for maintaining and improving your Honda TRX400EX’s power. Below is a detailed specification table for quick reference.

Below is a detailed specification table for quick reference.

From personal use, this kit stands out for its balance of cost-effectiveness and build quality. The parts fit precisely and perform reliably under typical riding conditions. It is a practical choice for anyone needing to service the top end of a 400EX without overspending on premium aftermarket kits.

It is a practical choice for anyone needing to service the top end of a 400EX without overspending on premium aftermarket kits.

2. 440cc Big Bore Cylinder Piston Ring Kit for Honda TRX400EX/X

Upgrade your Honda TRX400EX with a premium 440cc big bore cylinder piston ring kit designed for enhanced durability and performance. Built to outlast standard OEM kits, this package offers a perfect blend of strength and efficiency for riders who demand more power.

Carefully crafted with a ceramic-coated piston top, the kit excels in heat resistance, helping to prolong engine life under rigorous use. Ideal for models from 1999 to 2008, it delivers a noticeable boost in engine displacement and performance reliability.

The 440cc Big Bore Cylinder Piston Ring Kit includes all essential components needed for a smooth installation. It features a cylinder, piston, piston pin, and circlips, alongside a complete set of rings ensuring a tight seal and optimal compression.

Gasket sets for the head, base, head cover, and chain tensioner come included, maintaining engine integrity and preventing leaks during operation. Additional items like gasket maker and thread lock secure each part firmly to withstand high-stress conditions.

Designed to perform well in XC and GNCC racing conditions, the piston’s ceramic coating withstands extreme heat, promoting longevity. This kit also provides a fuel filter, oil filter, and a free NGK spark plug to cover maintenance requirements comprehensively.

Construction quality matches or surpasses OEM standards, making it a dependable choice for those upgrading or replacing worn components. The kit balances power enhancement and engine protection effectively.

Its compatibility with Honda TRX400EX models from 1999 through 2008 makes it suitable for riders looking to improve their quad’s responsiveness and overall capability. Installation is straightforward with all required parts included, offering excellent value for the investment.

Pros

• Ceramic-coated piston top for enhanced heat resistance and durability
• Complete kit with all necessary gaskets, filters, and accessories included
• Designed to improve power and engine lifespan, tested in XC and GNCC races

Cons

• Installation may require mechanical experience or professional assistance

This comprehensive package offers a significant performance uplift for Honda TRX400EX owners. Combining durability with enhanced engine capacity, it delivers excellent value to riders wanting a reliable upgrade. Below is a detailed specification summary for your convenience.

In my opinion, this kit stands out for its complete assembly and quality materials. It’s a solid choice for those aiming to boost their quad’s output while maintaining engine integrity. The inclusion of filters and spark plug makes it a comprehensive upgrade option compared to similar big bore kits.

3. 89mm 440CC Big Bore Cylinder Piston Gasket Kit for TRX400X

Upgrade your Honda TRX400EX or XR400R with the 89mm 440CC Big Bore Cylinder Piston Gasket Kit. Designed for enhanced engine performance, this kit offers a reliable and durable solution for those seeking increased power and smooth operation. It integrates high-quality components to ensure longevity under demanding conditions.

Perfectly compatible with various Honda models from 1999 to 2014, this kit provides a solid performance boost while maintaining ease of installation. Experience improved cylinder capacity and optimized piston operation for better throttle response and overall riding experience.

The kit includes an 89mm cylinder, piston, piston rings, two O-rings, wristpin, circlips, gasket, and spark plug. Each component is crafted from premium materials to withstand extreme conditions without compromising durability.

Installation is straightforward for those familiar with engine upgrades, minimizing downtime. Riders will notice increased engine displacement translating to stronger torque and better acceleration. Its robust construction resists wear and tear over time, reducing maintenance needs.

This kit suits riders looking for a practical and cost-effective performance enhancement without a complete engine rebuild. It balances quality and affordability while covering all necessary parts for a successful upgrade. The inclusion of multiple replacement gaskets and O-rings adds convenience.

The inclusion of multiple replacement gaskets and O-rings adds convenience.

Pros

• High-grade materials ensure long-lasting durability
• Comprehensive kit includes all needed components
• Compatible with multiple Honda TRX400EX and XR400R models

Cons

• Installation requires mechanical know-how and tools

Offering a blend of quality and practicality, this big bore kit provides a dependable upgrade path for Honda TRX400X owners. Components are designed to work harmoniously, delivering enhanced biking performance over stock parts. It stands as a worthwhile option for those focused on value and durability.

It stands as a worthwhile option for those focused on value and durability.

For those upgrading their Honda 400cc ATV, this kit offers a reliable enhancement without needing a full engine overhaul. Its comprehensive inclusion of parts simplifies the process, making it a solid pick for riders wanting more power and efficiency.

Despite requiring some mechanical skill for installation, the end results justify the effort.

4. Big Bore Cylinder for Honda TRX 400EX

Upgrade your Honda TRX 400EX with the Big Bore Cylinder kit designed for superior performance and durability. This comprehensive kit enhances engine displacement, providing a noticeable boost in power and efficiency. Carefully engineered components ensure smooth operation and long-lasting reliability.

Carefully engineered components ensure smooth operation and long-lasting reliability.

Perfectly suited for all models and years of the Honda Sportrax TRX400EX, the kit comes complete with vital engine parts. Whether for trail riding or competitive use, it brings an impressive upgrade to your quad’s top end assembly.

Professional installation is recommended to maximize benefits.

Designed to increase engine displacement, the Big Bore Cylinder kit offers a solid performance improvement over the stock setup. It includes everything needed for a full top end rebuild—cylinder, piston with rings, camshaft, valves, springs, and more. The cylinder head and high-temperature valve stem seals contribute to improved heat resistance and durability.

The included timing chain, tensioner, and guides optimize timing accuracy and reduce wear during operation. Also bundled are rocker arms, an oil filter, air filter, and spark plug, ensuring a comprehensive upgrade without additional parts hunting.

The machined exterior and quality materials enhance overall build integrity.

Installation upgrades throttle response and power delivery, making the quad more responsive on various terrains. Ideal for riders aiming to enhance the 400EX’s capability without extensive engine modifications.

Pros

• Complete top end kit with all essential components
• Increased displacement delivers improved power and performance
• Precision-machined cylinder for enhanced durability and fit

Cons

• Professional installation required for best results

This Big Bore Cylinder kit stands as a well-rounded solution for upgrading the Honda TRX 400EX. Its all-inclusive nature simplifies the rebuild process while improving engine output and reliability. Comparable kits might offer fewer components or lack this level of detail, positioning this upgrade as an efficient choice.

From personal experience, this kit delivers a noticeable boost in engine performance and feels like a reliable upgrade. Its comprehensive parts list reduces the hassle of sourcing individual components, making installation straightforward when handled by a professional. Worth considering for serious TRX 400EX riders seeking an effective power upgrade.

Worth considering for serious TRX 400EX riders seeking an effective power upgrade.

5. Cylinder Piston Ring Kit with Seal for Honda XR400R TRX400X 400EX

Upgrade your Honda ATV or motorcycle with a reliable cylinder piston ring kit designed for enhanced engine performance. This kit supports various Honda models, providing essential components for a smooth top-end rebuild.

Its precise fit and durable materials offer lasting results under demanding conditions.

Ideal for restoring power and efficiency, this kit ensures your Honda XR400R, TRX400X, or 400EX operates at peak capacity. Whether maintaining or refurbishing, it delivers consistent quality to keep your engine running strong and responsive.

The 89MM cylinder piston ring kit includes all vital components for a comprehensive top-end service. It fits Honda ATV Sportrax 400 TRX400EX models from 1999 to 2008, TRX400X from 2009 to 2014, and XR400R motorcycles from 1996 to OEM part numbers covered indicate thorough compatibility with factory standards.

The cylinder is crafted from high-grade cast aluminum, providing excellent heat dissipation and durability. The piston, made of lightweight aluminum, balances strength with performance for reliable operation. Each part is engineered and tested to meet or surpass original equipment standards.

Regular replacement of pistons and rings is essential, as wear can reduce engine efficiency and increase oil consumption. This kit includes gaskets, rings, seals, and additional hardware such as spark plug and valve oil seals.

Assembly is straightforward due to included positioning pins and clear part organization, allowing even those with moderate mechanic skills to manage the installation. The design ensures better sealing and engine longevity while restoring compression for improved throttle response. This set offers great value compared to purchasing parts individually or opting for aftermarket alternatives with uncertain quality.

Pros

• Comprehensive kit with all necessary gaskets and seals included
• Durable cast aluminum cylinder and piston engineered to factory standards
• Compatible with multiple Honda models ensuring wide usability

Cons

• Requires mechanical knowledge for proper installation

Offering a balanced combination of quality, compatibility, and complete hardware, this cylinder piston ring kit supports dependable engine rebuilding. Its sturdy materials and inclusive components promote longevity and better performance for Honda ATV and motorcycle owners.

Choosing this kit can rejuvenate your engine efficiently while ensuring a precise fit and proper seal on critical engine components.

Based on its specifications and included components, this kit represents a solid option for maintaining or restoring Honda 400ex and related models. For users comfortable with engine rebuilds, it provides a reliable source of genuine-quality parts. Its comprehensive nature reduces extra sourcing, making it a practical choice for maintaining engine integrity and performance longevity.

Its comprehensive nature reduces extra sourcing, making it a practical choice for maintaining engine integrity and performance longevity.

6. Big Bore Top End Rebuild Kit for Honda TRX 400EX

Upgrade your Honda Sportrax TRX400EX with the Big Bore Top End Rebuild Kit designed to enhance engine performance. This comprehensive kit focuses on increasing displacement for a more powerful and responsive ride.

Every component is crafted for compatibility with all TRX400EX models and years, offering a reliable upgrade path. The kit also includes everything needed for a complete top-end rebuild, simplifying maintenance and improvements.

The kit features a big bore cylinder and piston fitted with rings, which work together to boost engine size beyond the stock configuration. High-temperature valve stem seals ensure durability and better heat resistance during operation. It comes complete with top end gaskets and a timing chain to facilitate a smooth rebuild process without sourcing separate parts.

Precision machining highlights the quality of the components, matching OEM specifications closely for dependable performance. Installation is straightforward for a professional mechanic and helps bring new life to the Sportrax TRX400EX’s engine. This package provides a solid balance of performance gains and lasting reliability.

Ideal for riders wanting to enhance their ATV’s power delivery and throttle response, this kit fits all models of the Honda TRX400EX. The enhanced displacement delivers noticeable improvements in torque and acceleration, improving overall riding experience both on trails and rough terrain.

Pros

• Increases engine displacement for stronger performance.
• Includes all necessary components for a full top end rebuild.
• High heat resistant valve stem seals improve durability.

Cons

• Professional installation is recommended, which may add to overall costs.

The Big Bore Top End Rebuild Kit for the Honda TRX 400EX offers a valuable upgrade with carefully matched parts designed to boost engine output and extend service life. This enhancement package suits riders seeking a reliable power increase with quality components.

This kit presents a straightforward and effective method to improve TRX400EX performance. Compared with similar options, it offers a fuller rebuild package rather than just cylinder or piston upgrades alone.

7. Big Bore Top End Rebuild Kit for Honda TRX 400EX

Enhance your Honda TRX 400EX’s engine performance with the Big Bore Top End Rebuild Kit. Designed to boost displacement and efficiency, this kit supplies everything needed for a complete top-end upgrade.

This comprehensive kit is well-suited for riders seeking robust power gains and long-lasting reliability. Whether for trail riding or more demanding terrain, it improves your ATV’s engine response and durability. Its professional-grade components set the stage for improved performance and smoother running.

The Big Bore Top End Rebuild Kit features a big bore cylinder and piston assembly with rings, boosting engine displacement beyond stock levels. Included valves, springs, and a camshaft ensure enhanced breathing and timing accuracy. High-temp valve stem seals promote durability in intense conditions for combustion efficiency.

High-temp valve stem seals promote durability in intense conditions for combustion efficiency.

Along with the timing chain, tensioner, and guides, the kit rebuilds critical timing functions for smooth operation. Rocker arms and top-end gaskets provide precise sealing and valve actuation.

A new oil filter, air filter, and spark plug complete the overhaul for comprehensive maintenance.

Crafted by CL2 Powersports, this kit balances build quality with ease of use. It offers reliability and better overall performance for riders who demand more from their TRX 400EX. Professional installation is advised to ensure optimal results.

Professional installation is advised to ensure optimal results. Ideal for riders upgrading or refurbishing their ATV engine with a trusted brand choice.

Pros

• Complete top-end rebuild kit with all necessary components included
• Big bore design increases engine displacement and power output
• High-quality parts improve durability and reliability under load

Cons

• Requires professional installation for best performance and fitment

Offering an extensive range of upgraded engine parts, this kit provides a solid option for enhancing the TRX 400EX top end. It boosts both horsepower and reliability, making it a valuable upgrade for riders seeking advanced engine performance. When compared to similar kits, it stands out by including a full set of components required for a thorough rebuild.

When compared to similar kits, it stands out by including a full set of components required for a thorough rebuild.

For those looking to maximize their Honda TRX 400EX’s engine potential, this kit is a solid choice. It provides everything needed to complete a top-end rebuild with performance upgrades included.

8. Cylinder Piston Gasket Kit for Honda Sportrax TRX400EX

Enhance your Honda Sportrax TRX400EX’s performance with the Cylinder Piston Gasket Kit designed to provide a reliable and precise fit. Tailored for models from 1999 to 2008, this replacement kit delivers a big bore upgrade that increases engine displacement to 440cc.

This comprehensive kit includes a piston set, gasket kit, and OE type cylinder, offering a complete overhaul solution in a single package. Installation should be performed by professionals with experience in ATVs and UTVs to guarantee proper setup and longevity.

Designed to fit the Sportrax TRX400EX models, this cylinder piston gasket kit comes with an 89mm by 70mm big bore cylinder. The upgraded 440cc displacement combined with a 10:1 compression ratio enhances engine efficiency and power delivery.

Its OE type cylinder maintains the quality and compatibility expected from original equipment.

Crafted by GPA MOTORS, the kit emphasizes durable construction that withstands the rigors of off-road riding. The parts included are precision-machined to ensure smooth operation and minimize wear.

The installation process is straightforward for professional mechanics but requires specialized ATV and UTV knowledge to avoid complications. Ideal for riders aiming to boost their vehicle’s performance and reliability, the kit offers excellent value by encompassing all necessary components in one set.

Pros

• Complete kit includes piston, gasket, and OE cylinder
• Big bore upgrade to 440cc for enhanced engine power
• Durable, OEM-quality construction for lasting performance

Cons

• Requires professional installation by specialized mechanics

This kit provides a dependable and well-rounded solution for improving the power and durability of the Honda Sportrax TRX400EX’s engine. With all essential components included and a trusted build quality, it stands as a strong choice among similar big bore kits. Prioritizing professional installation maximizes results and longevity.

Prioritizing professional installation maximizes results and longevity.

For riders requiring a reliable OEM replacement with increased displacement, this kit offers a robust upgrade. Its combination of quality parts and enhanced specifications ensures that your Sportrax TRX400EX runs smoother and stronger.

9. Vertex Big Bore Piston Kit for Honda TRX 400 EX/X

The Vertex Big Bore Piston Kit for Honda TRX 400 EX/X transforms your ATV’s performance by boosting engine displacement and power. Designed to maintain stock compression ratios, it delivers a balanced upgrade that enhances speed and reliability.

This piston kit is crafted with Vertex’s forged technology and a +2mm bore, increasing the engine’s capacity to 416cc for improved output. Each kit contains everything needed for installation: piston, ring set, wrist pin, and circlips, guaranteeing a complete solution without extra purchases.

The Molybdenum Disulphide (MOS2) coating on the piston skirt ensures reduced wear and smoother break-in, protecting engine components over time.

Constructed to match or surpass OEM specifications, the kit fits Honda TRX 400 EX models from 1999 to 2008 and TRX 400 X models from 2009 to This compatibility assures proper fit and optimal performance without guesswork. Its forged piston build provides durability for aggressive riding, making it suitable for trail riders seeking extra power without sacrificing engine longevity.

Its forged piston build provides durability for aggressive riding, making it suitable for trail riders seeking extra power without sacrificing engine longevity.

Installation is straightforward and designed to integrate seamlessly with existing engine components. Riders will appreciate the improved throttle response and power delivery resulting from the increased displacement.

Additionally, the inclusion of all necessary parts ensures no additional components are required, simplifying maintenance or upgrades. With a dependable design, this kit balances performance gains and long-term reliability.

The Vertex Big Bore Piston Kit provides excellent value for those aiming to boost their Honda ATV’s engine without complex modifications. Its durability, fit, and detailed engineering set it apart from standard replacement pistons and single-component upgrades.

This makes it an ideal choice for riders focused on consistent and noticeable improvements in their machine’s capabilities.

Pros

• Increases engine displacement to 416cc for enhanced power
• Comes complete with piston, rings, wrist pin, and circlips
• Durable forged piston with MOS2 coating for reduced wear and smooth break-in

Cons

• Limited to Honda TRX 400 EX (1999–2008) and TRX 400 X (2009–2014) models

For riders who want a reliable and effective big bore upgrade, the Vertex Big Bore Piston Kit offers excellent craftsmanship and consistent performance. It stands out by providing a well-matched fit and enhanced engine capacity without compromising engine integrity.

In comparison to basic replacement pistons, this big bore kit adds a noticeable power boost while maintaining engine reliability. The attention to detail in fit and coating enhances durability that some cheaper alternatives do not provide.

This makes the Vertex kit a smart upgrade for serious riders wanting more from their Honda ATV.

10. US Replace Parts Big Bore Piston Kit for Honda TRX 400 EX

Upgrade your Honda TRX 400 EX with the US Replace Parts Big Bore Piston Kit, designed specifically for models from 1999 to This kit offers an enhanced engine performance boost, crafted to extend the life of your ATV’s motor.

Precision engineered for a seamless fit, it delivers reliable power and efficiency.

Ideal for riders seeking to restore or improve their bike’s performance, this piston kit provides consistent quality and durability. Its straightforward installation makes it accessible for users with basic mechanical skills, ensuring a hassle-free upgrade experience.

The US Replace Parts Big Bore Piston Kit is an efficient replacement option for your TRX 400 EX. Designed to match the exact specifications of the original parts, it guarantees compatibility and optimal engine function.

Delivering enhanced compression, the piston kit improves power output and responsiveness with every ride. Its precise engineering minimizes wear and tear, contributing to longer engine life. The sleek design maintains smooth operation and reduces vibrations, enhancing overall ride quality.

Installation is straightforward, requiring minimal adjustments and downtime. This kit is perfect for ATVs used in demanding terrains or for riders wanting to regain lost engine efficiency. Compared to standard alternatives, it offers dependable performance without frequent maintenance concerns.

Compared to standard alternatives, it offers dependable performance without frequent maintenance concerns.

Pros

• Engineered for perfect fit on Honda TRX 400 EX (1999-2008)
• Durable construction resists wear and high stress
• Improves power output and engine responsiveness

Cons

• Limited to specific model years requiring careful compatibility check

This piston kit is a solid choice for those aiming to maintain or enhance their ATV’s engine without complicated modifications. It balances durability and performance in a user-friendly package.

From my experience, this piston kit offers a dependable upgrade for Honda TRX 400 EX owners. It combines ease of installation with solid performance gains, making it an effective choice for those looking to keep their ATV running smoothly without complex rebuilds.

11. Big Bore 85mm 397cc Cylinder Piston Gasket Kit for Sportrax TRX400EX

Enhance your Sportrax TRX400EX’s engine capacity with the Big Bore 85mm 397cc Cylinder Piston Gasket Kit. This upgrade kit offers a substantial boost in displacement, improving your bike’s torque and overall power. Designed for users seeking a complete top-end rebuild, it delivers both performance and reliability.

Designed for users seeking a complete top-end rebuild, it delivers both performance and reliability.

Every component within the kit is carefully matched to support seamless engine operation. From the precisely bored 85mm cylinder to the durable piston and detailed gaskets, quality is maintained throughout the package.

Engine upgrades demand precision and well-fitted parts. This kit includes a matched piston, rings, wrist pin, circlips, and all necessary head and base gaskets.

The 85mm cylinder increases displacement to 397cc, which translates into a notable torque and horsepower gain. Each gasket guarantees a tight seal, preventing compression loss and leaks.

Constructed for users comfortable with engine disassembly, installation will require mechanical skill and the right tools. Carburetor re-jetting is recommended after installation to fully harness the increased power potential. It is compatible with sportrax TRX400EX models from 1999 to 2008, providing a focused upgrade rather than a simple bolt-on solution.

This ensures the engine performs well with its enhanced specifications, making it ideal for performance-minded riders.

The kit’s robust build quality reflects the demands of high-performance environments. This upgrade kit offers exceptional value by combining all necessary components in one set, saving time and effort sourcing parts separately. For those aiming for an engine rebuild that combines enhanced displacement and reliability, this kit presents a solid choice.

Pros

• Comprehensive kit with all essential components for top-end rebuild
• Significant increase in engine displacement for better torque and power
• High-quality gaskets ensure reliable sealing and engine compression

Cons

• Installation requires mechanical skills and engine disassembly

This Big Bore Cylinder Piston Gasket Kit offers a practical and effective upgrade path for Sportrax TRX400EX models. It stands out among similar kits by providing matched components that maintain engine integrity during performance increases.

In my experience, this kit offers a solid balance between performance enhancement and component compatibility. Those comfortable with DIY engine work will find it particularly rewarding. It’s a reliable upgrade that makes each ride more responsive without compromising engine stability.

It’s a reliable upgrade that makes each ride more responsive without compromising engine stability.

12. NewJs 85mm 400cc Big Bore Cylinder Piston Rings Kit for Honda TRX400EX

Upgrade your Honda TRX400EX with the NewJs 85mm 400cc Big Bore Cylinder Piston Rings Kit. Designed to boost engine performance, this kit offers a reliable replacement solution for worn or damaged parts.

Its precision engineering ensures a perfect fit for model years 1999 through

Ideal for riders seeking enhanced displacement, the kit elevates the ATV’s power and efficiency. With quality materials and sturdy construction, it promises durability and lasting performance on various terrains.

The NewJs big bore kit includes a cylinder, piston, piston rings, and gaskets tailored to fit flawlessly on the Honda TRX400EX. Featuring an 85mm bore and 70mm stroke, it produces a displacement of 397cc paired with a 1:1 compression ratio.

This setup improves throttle response and overall engine output while maintaining smooth operation.

Each component is crafted with attention to detail, matching OEM specifications for straightforward installation. Its aftermarket design works as a direct substitute for old or malfunctioning parts, saving time and effort. Users will appreciate that it supports endurance across tough off-road conditions without compromising reliability or sealing performance.

Thanks to its balanced performance and build quality, this kit suits both weekend riders and those who demand consistent results from their ATVs. The components fit precisely to avoid leaks or premature wear, ensuring a strong seal to maximize compression and power delivery with every ride.

Pros

• Complete top-end kit with cylinder, piston, rings, and gaskets
• High-quality materials built to OEM dimensions for an exact fit
• Increases engine displacement to 397cc for improved performance

Cons

• Installation may require mechanical experience or professional assistance

This big bore kit enhances the Honda TRX400EX’s engine capabilities while ensuring compatibility with original components. Its durable construction and comprehensive parts list make it a practical choice for restoring or upgrading the bike’s powertrain.

For users upgrading their ATV’s engine size, this kit strikes a solid balance between value and performance. It offers precision fitment and dependable operation, making the Honda TRX400EX feel refreshed and stronger. When compared to other big bore kits, the NewJs stands out for its compatibility and comprehensive top-end parts, providing a smooth upgrade experience.

Top Big Bore Kits for 400EX: Ultimate Buying Guide 2024

Engine compatibility

The best big bore kit for 400ex is designed to enhance the performance of Honda ATVs, particularly those from model years 1999 to 2004 that come with a stock 397cc four-stroke single-cylinder engine. These kits typically increase engine displacement, which boosts power and torque for more robust acceleration and higher top speeds. When selecting a kit, it’s worthwhile to consider how it integrates with existing engine components, especially if there have been previous aftermarket modifications such as upgraded carburetors, exhaust systems, or ignition parts.

When selecting a kit, it’s worthwhile to consider how it integrates with existing engine components, especially if there have been previous aftermarket modifications such as upgraded carburetors, exhaust systems, or ignition parts. Compatibility with these upgrades can affect the overall efficiency and reliability of the ATV’s powertrain. Some kits also accommodate reinforcements in the engine casing and cylinder head to handle increased stress from the larger bore.

This compatibility ensures that both new and slightly modified stock engines benefit without sacrificing durability. These kits cater to riders seeking more power for trail riding or racing without needing an entirely new engine setup. It’s recommended to verify the kit’s fit for your specific model year and current modifications to maintain smooth installation and optimal performance gains.

Kit components and quality

Choosing the right big bore kit for a 400ex involves paying close attention to the included parts such as pistons, cylinders, and gaskets, which form the core of the upgrade. High-quality materials and precise manufacturing standards contribute greatly to durability and performance, ensuring the parts can withstand extensive use and heat. Brands known for their reliability often back their products with warranties, giving additional confidence in the purchase.

Brands known for their reliability often back their products with warranties, giving additional confidence in the purchase. This combination of sturdy components and trustworthy support helps provide a smoother, more powerful engine boost that suits various riding styles and conditions.

Performance improvements

Choosing the best big bore kit for 400ex involves understanding how it affects horsepower and torque gains, which typically translate into a more powerful engine response. Riders can expect noticeable improvements in throttle response and acceleration, making the quad feel livelier on various terrains.

Considering the intended use, such as trail riding or racing, helps determine the ideal kit that complements the desired riding experience and enhances the engine’s capabilities effectively.

Installation requirements

Choosing the best big bore kit for 400ex involves understanding the tools and technical skills needed to complete the upgrade successfully. Basic mechanical knowledge and a set of common hand tools like wrenches, screwdrivers, and torque wrenches are usually required.

Some kits may also necessitate more specialized equipment such as piston ring compressors or measurement tools to check clearances. Compatibility with the existing engine setup is another important factor since not all kits fit every model perfectly. Checking whether the kit includes everything you need, such as gaskets and cylinder head hardware, helps avoid additional purchases later.

Considering whether to install the kit yourself or seek professional assistance depends on your comfort level with engine work. While many find installation manageable with the proper manuals and patience, others prefer leaving it to experts to guarantee precision and reduce the risk of damage.

Cost and value for money

When evaluating different big bore kits for a 400ex, it’s helpful to compare their price points alongside what you get for the investment. Some kits offer a balance between affordability and durable components, making them a sensible choice for riders who want reliable performance without frequent expenses.

Checking how easily replacement components can be sourced is another key aspect since readily available parts reduce downtime and simplify repairs. Whether purchasing a renowned brand or a lesser-known alternative, kits with accessible aftermarket support and straightforward maintenance procedures tend to provide better overall value in the long run.

Customer support and reviews

When choosing the best big bore kit for 400ex, paying attention to manufacturer customer service responsiveness can make a significant difference in your buying experience. Reliable companies often provide clear guidance and assistance throughout the installation process, addressing any technical questions or concerns. User feedback and satisfaction levels are valuable sources of information, as they reflect real-world performance and durability of the kit.

User feedback and satisfaction levels are valuable sources of information, as they reflect real-world performance and durability of the kit. Customers frequently comment on the ease of installation, the improvement in power and throttle response, and overall value for money. Some common issues that may arise include problems with jetting or fitting, but many manufacturers supply troubleshooting tips or support forums that help resolve these quickly.

Taking these factors into account can help ensure a smoother upgrade and a more enjoyable ride on your 400ex.

People Also Asked

The top-rated big bore kits for the Honda 400EX include the ProX Big Bore Kit and the Wiseco Big Bore Kit, both known for boosting engine displacement and improving overall performance. These kits typically offer enhanced power, reliability, and durability for off-road riding.

A big bore kit increases the engine displacement of the 400ex, allowing it to intake more air and fuel, which boosts power and torque. This results in improved acceleration, higher top speed, and better overall performance.

When choosing a big bore kit for your 400ex, consider compatibility with your engine model and the quality of materials used to ensure durability and performance. Additionally, evaluate the kit’s impact on engine tuning, power output, and whether it requires additional modifications or maintenance.

Yes, reputable brands like Pro X and Wiseco specialize in big bore kits for the Honda 400EX, offering high-quality components to enhance engine performance. These kits are popular among riders looking to increase displacement and power efficiently.

When installing a big bore kit on a 400ex, ensure all components are clean and properly lubricated, and carefully follow torque specifications to avoid damage. Common issues include improper jetting leading to poor performance and overheating, so be prepared to rejet and tune the carburetor accordingly.

Conclusion

Choosing the best big bore kit for 400ex can greatly enhance your bike’s power and overall performance. These kits typically offer increased displacement, better torque, and improved throttle response, making your rides more thrilling and efficient. However, some kits may require additional tuning or modifications to achieve peak performance, and installation can be moderately challenging for beginners.

The ideal candidate for a big bore kit is someone familiar with mechanical work or willing to seek professional installation. For those wanting more power without extensive engine rebuilding, selecting a reliable and well-reviewed kit will address most concerns.

Balancing the benefits of enhanced performance with potential installation efforts will help you make a confident choice tailored to your riding needs.