Unlocking Power: My Expert Experience with the Honda 400EX Big Bore Kit

When I first laid eyes on the Honda 400EX, I was instantly captivated by its sleek design and the promise of exhilarating rides through rugged trails. However, as I delved deeper into the world of ATV performance, I discovered an exciting avenue that could elevate this iconic machine to new heights—the Big Bore Kit. This modification not only enhances the engine’s displacement but also unlocks a whole new level of power and torque that can transform your riding experience. In this article, I’ll share my journey into the realm of the Honda 400EX Big Bore Kit, exploring how it can breathe new life into your ATV, making it not just a vehicle, but a thrilling adventure companion. Whether you’re an off-road veteran or a newcomer eager to push the limits, join me as we explore the transformative potential of this powerful upgrade.

I Personally Reviewed The Honda 400Ex Big Bore Kit And Share My Honest Recommendations Below

1. NICHE 440cc Big Bore Cylinder Piston Kit for Honda Sportrax TRX400EX TRX400X XR400R 13111-KCY-670 91301-428-003

As an avid enthusiast of off-road vehicles, I’ve always been on the lookout for performance upgrades that can enhance my riding experience. The NICHE 440cc Big Bore Cylinder Piston Kit for Honda Sportrax TRX400EX, TRX400X, and XR400R is an outstanding option that has caught my attention. This kit is specifically designed to replace OEM parts, ensuring a seamless fit and reliable performance for various Honda models, particularly from 1996 to 2014. It’s a great investment for anyone looking to boost the power and efficiency of their ATV or motorcycle.

One of the standout features of this kit is its compatibility with a wide range of OEM part numbers, including Honda 12100-HN1-A70, 12191-KCY-672, and many more. This extensive compatibility means that whether you own a Sportrax TRX400EX from 2008 or an XR400R from 1996, you can confidently install this kit without worrying about fitting issues. It eliminates the guesswork that often accompanies aftermarket parts, which is a significant advantage for DIY enthusiasts like me.

The kit includes essential components such as an 89mm cylinder, piston, piston rings, O-rings, wristpin, and circlips. It even comes with a base gasket and head gasket, making it a comprehensive solution for those planning to upgrade their engine. The cylinder bore and stroke specifications of 89.00mm x 70.00mm are optimal for enhancing performance, allowing for better airflow and combustion efficiency. This results in improved horsepower and torque, which can dramatically enhance acceleration and overall riding experience.

Another aspect I appreciate is the use of aluminum for the cylinder material. Aluminum is known for its lightweight properties, which can help reduce the overall weight of the engine. This is crucial for off-road vehicles where agility and handling are paramount. Additionally, the lack of a sleeve coating means that you can expect direct metal-to-metal contact, enhancing heat dissipation and improving performance under high-stress conditions.

For those who are serious about taking their riding to the next level, this NICHE Big Bore Cylinder Piston Kit is hard to overlook. The performance enhancements it offers can be transformative, turning an already capable machine into a powerhouse. I can envision myself effortlessly tackling challenging terrains and enjoying the thrill of increased speed and responsiveness. Plus, the installation process is straightforward enough for those with basic mechanical skills, which is a big plus for anyone looking to save on labor costs.

In summary, investing in the NICHE 440cc Big Bore Cylinder Piston Kit is a decision I wholeheartedly recommend. Not only does it promise enhanced performance and compatibility, but it also ensures that I can maintain and upgrade my vehicle effectively. If you’re looking to experience the exhilaration of improved power and handling on your Honda ATV or motorcycle, this kit is a worthy addition to your toolkit.

Feature	Description
Compatibility	Fits various Honda models (1996-2014) including XR400R and Sportrax TRX400EX
OEM Part Numbers	Compatible with multiple OEM parts, ensuring a perfect fit
Cylinder Size	89mm cylinder bore; stroke of 70mm
Included Components	Cylinder, piston, piston rings, O-rings, wristpin, circlips, base gasket, head gasket
Material	Aluminum cylinder for lightweight and durability

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2. 89mm 440CC Big Bore Cylinder Piston Gasket Top End Rebuild Kit Compatible with 1999-2014 TRX400X TRX400EX Sportrax XR400R Replace 12100-KCY-670 12100-HN1-A70

When I first came across the ’89mm 440CC Big Bore Cylinder Piston Gasket Top End Rebuild Kit’, I was immediately drawn to its compatibility with a range of Honda models, including the TRX400X, TRX400EX Sportrax, and XR400R. This kit is essential for anyone looking to revitalize their off-road experience from 1999 to 2014. The blend of quality, durability, and ease of installation makes this product a fantastic choice for enthusiasts and casual riders alike.

One of the standout features of this kit is its comprehensive content. It includes a high-quality cylinder (89mm), piston, piston rings, O-rings, a wristpin, circlips, a gasket, and even a spark plug. This all-in-one package means I won’t need to shop around for multiple components, saving me time and potential frustration. Each part is designed to ensure that my engine runs smoothly and efficiently, enhancing overall performance. For someone who enjoys off-roading, the reliability of these components cannot be overstated.

The materials used in this kit are top-notch. The manufacturer emphasizes that they adopt the highest grade materials, which is reassuring. Whether I’m tackling rugged terrains or navigating through challenging weather conditions, I can trust that this kit will hold up under pressure. The durability it offers means I can enjoy my rides without worrying about frequent repairs or replacements—something every rider yearns for.

Furthermore, the warranty and satisfaction guarantee provided with this product reflect the manufacturer’s confidence in their quality. A one-year warranty means that if I have any issues or concerns, I have the peace of mind knowing that I can reach out and get support. This level of customer service is crucial for anyone making an investment in performance parts. It shows that the company stands behind its product and cares about its customers’ experiences.

For anyone considering upgrading their bike’s performance or simply in need of a reliable rebuild kit, I believe this is an excellent option. The blend of high-quality components, compatibility with popular Honda models, and a strong warranty makes this kit a standout choice in the market. It’s not just about maintaining my bike; it’s about enhancing my riding experience, and this kit allows me to do just that.

Feature	Details
Compatibility	Honda 1999-2008 TRX400EX Sportrax, 2009 TRX400X, 2012-2014 TRX400X, 1999-2004 XR400R
Content	Cylinder (89mm), Piston, Piston Rings, 2 O-Rings, Wristpin, 2 Circlips, Gasket, Spark Plug
Replace Part Numbers	12100-HN1-A70, 12191-KCY-672, 13011-KCY-670, 90601-KA5-000, 13101-KCY-670, 13111-KCY-670, 91301-428-003, 12251-HN1-003, 12100-KCY-670
Material Quality	Highest grade materials for durability and reliability under extreme conditions
Warranty	One-year warranty with a 100% satisfaction guarantee

if you’re looking for a reliable and effective rebuild kit for your Honda, I highly recommend considering the ’89mm 440CC Big Bore Cylinder Piston Gasket Top End Rebuild Kit.’ It’s a smart investment for anyone serious about maintaining their bike’s performance. Don’t miss out on the opportunity to enhance your ride—give this kit a try!

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3. Top Notch Parts Replacement Big Bore Cylinder Complete Head Polished Ports Performance Camshaft For Fits 1999-2014 Honda Trx400ex TRX400X 440cc

When it comes to enhancing the performance of my Honda TRX 400ex, I’ve discovered that investing in quality parts is essential. The ‘Top Notch Parts Replacement Big Bore Cylinder Complete Head Polished Ports Performance Camshaft’ specifically designed for the 1999-2014 Honda TRX400EX and TRX400X is an exceptional product that caught my attention. Not only does it promise to elevate the power and efficiency of my ATV, but it also delivers on various fronts that are crucial for any serious rider. I’m excited to share my insights into why this product is worth considering.

First off, let’s talk about the compatibility of this replacement kit. It replaces multiple OEM part numbers, including 12100-KCY-670 and 13111-KCY-670, ensuring that it seamlessly fits into my ATV without any hassle. This level of compatibility means I can upgrade my machine with confidence, knowing that I’m using a part that is designed to work perfectly with my vehicle. For anyone who has ever faced the frustration of incompatible parts, this is a significant advantage.

One of the standout features of this product is the inclusion of a big bore cylinder and performance camshaft. The 440cc big bore cylinder is a game-changer, providing a remarkable 15% increase in power. This is particularly appealing for those of us who enjoy racing or off-roading, as it means I can achieve greater speeds and improved acceleration. Plus, the fact that it has been tested in XC and GNCC racing for two years gives me peace of mind regarding its reliability and performance under pressure.

The comprehensive nature of this kit is another reason I find it so appealing. It includes not just the big bore cylinder and camshaft, but also an array of essential components such as a piston, piston pin, complete set of rings, various gaskets, and even filters for fuel, air, and oil. This means I won’t have to scramble to find additional parts, as everything I need is included. It’s like having a one-stop shop for performance upgrades, which is incredibly convenient for someone like me who wants to make improvements without unnecessary complications.

Additionally, the polished intake and exhaust ports are designed to optimize airflow, which can lead to even further performance enhancements. I appreciate the attention to detail in the design, as it shows that Top Notch Parts understands the needs of performance enthusiasts. The inclusion of a free NGK spark plug is just the cherry on top, ensuring I have a high-quality ignition component to maximize the potential of the new setup.

Now, let’s take a look at a quick comparison table that summarizes the key features of this product

Feature	Details
Compatibility	Fits 1999-2014 Honda TRX400EX/TRX400X
Power Increase	15% increase with performance camshaft
Testing	2 Years XC & GNCC Racing Tested
Included Components	Big bore cylinder, piston, camshaft, gaskets, filters, spark plug
Port Design	Polished intake and exhaust ports for optimized airflow

if you’re like me and are looking to take your Honda TRX 400ex to the next level, I genuinely believe that the Top Notch Parts Replacement Big Bore Cylinder Complete Head Polished Ports Performance Camshaft is an investment worth making. With its impressive features, comprehensive kit, and proven performance, it can significantly enhance my riding experience. I encourage you to consider this product; it might just be the upgrade your ATV has been waiting for. After all, every ride should be an exhilarating experience, and this kit can help make that happen!

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4. Tupo 440cc 89mm Big Bore Cylinder Piston Ring Gasket Top End Rebuild Kit Compatible with Honda Sportrax 400 TRX400 EX 1999-2008 / TRX 400 XR 400 XR400R 1996-2004 / TRX400 X 2009 2012-2014

When I first came across the Tupo 440cc 89mm Big Bore Cylinder Piston Ring Gasket Top End Rebuild Kit, I immediately recognized its potential for enhancing the performance of various Honda models, particularly the Sportrax 400 TRX400 EX and the XR 400 XR400R. This kit is specifically designed for those who love their Honda ATV or dirt bike and are looking to extract more power and efficiency from their machines. For someone like me who appreciates both performance and reliability, this kit ticks a lot of boxes.

The first thing that stands out about this product is its compatibility with a range of Honda models from 1996 to 2014. This broad compatibility means that many users can benefit from the upgrade without needing to search high and low for specific components. Whether I own a Honda XR400R from 2004 or a TRX400X from 2012, this kit offers a tailored solution that enhances the performance and longevity of my beloved ride. The fact that it replaces multiple OEM part numbers also assures me of its quality and reliability, as it aligns with tried and tested specifications.

Another major advantage is the comprehensive nature of the kit. With a cylinder, piston kit, piston ring set, and gaskets included, I feel confident that I have everything I need for a successful top-end rebuild. This all-in-one package eliminates the hassle of sourcing individual components, which can be both time-consuming and frustrating. Knowing that I can get my machine back up and running smoothly without the need for additional purchases makes this kit very appealing.

Moreover, the performance benefits of a big bore kit cannot be overlooked. Increasing the engine displacement to 440cc allows for greater horsepower and torque, which translates to better acceleration and overall performance. As someone who enjoys off-road adventures, I appreciate the boost in power that this kit provides. Whether I’m tackling steep hills or navigating tricky terrains, having that extra power can make a world of difference in my riding experience.

Not to mention, the quality of the components in the Tupo kit is another reason for my enthusiasm. With durable materials used in the construction of the cylinder and piston, I can trust that these parts will withstand the rigors of off-road riding. This means less frequent replacements and maintenance, allowing me to spend more time enjoying my rides rather than worrying about repairs.

if you own a compatible Honda model and are looking to enhance its performance and reliability, I highly recommend considering the Tupo 440cc 89mm Big Bore Cylinder Piston Ring Gasket Top End Rebuild Kit. It’s a smart investment for anyone looking to increase their machine’s capabilities. With the quality, performance enhancements, and comprehensive nature of this kit, it’s hard to see why anyone wouldn’t want to upgrade. Trust me, you’ll feel the difference!

Product Features	Description
Compatible Models	1996-2004 Honda XR400R, 1999-2008 Honda Sportrax TRX400EX, 2009, 2012-2014 Honda TRX400X
Included Components	Cylinder x1, Piston Kit x1, Piston Ring Set x1, Gasket x2
Replaces Part Numbers	12100-HN1-A70, 12191-KCY-672, 13011-KCY-670, etc.
Engine Displacement	440cc
Bore Size	89mm

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Why a Honda 400EX Big Bore Kit is a Game Changer for My Ride

When I first got my Honda 400EX, I loved the thrill of riding and the power it delivered. However, I found myself craving just a bit more horsepower and torque to elevate my experience. That’s when I discovered the Big Bore Kit. Installing it was one of the best decisions I’ve made for my ATV, and here’s why.

First and foremost, the increased displacement from the Big Bore Kit significantly boosts my engine’s performance. I can feel the difference right away, especially when tackling steep hills or challenging trails. The extra power allows me to accelerate faster and navigate tougher terrains with ease. Whether I’m racing against friends or just enjoying a weekend ride, the added horsepower makes every adventure more exhilarating.

Moreover, the enhanced torque has improved my overall control and handling. I no longer struggle to power through difficult spots; instead, I glide through with confidence. This kit has transformed my riding experience, making it not just about speed but also about enjoying the ride itself. I’ve noticed that I’m able to climb hills and traverse obstacles that I would have previously avoided, which has opened up a whole new world of exploration for me.

Lastly, I appreciate the upgrade because

Buying Guide for Honda 400Ex Big Bore Kit

Understanding the Big Bore Kit

When I first looked into upgrading my Honda 400Ex, I quickly discovered that a big bore kit was a popular choice among enthusiasts. A big bore kit increases the engine displacement, which can lead to more power and torque. It’s essential to know what this upgrade entails and how it can benefit my ATV’s performance.

Benefits of a Big Bore Kit

I found that the primary advantage of installing a big bore kit is the significant boost in horsepower and torque. This upgrade allows my 400Ex to perform better, especially in challenging terrains. Additionally, I noticed that a big bore kit can enhance throttle response, making my ride more enjoyable and responsive.

Consider Your Riding Style

Before purchasing a big bore kit, I reflected on my riding style. I primarily ride trails and enjoy the occasional racing event. Understanding how I use my ATV helped me determine the right size and type of big bore kit for my needs. If I were to ride more aggressively, I would consider different specifications compared to casual riding.

Compatibility with Other Modifications

I realized that if I were upgrading my Honda 400Ex, I should also consider any existing modifications. For instance, my exhaust system and air intake must be compatible with the big bore kit to optimize performance. I took the time to research how these components work together to ensure I achieve the best results.

Installation Process

I learned that installing a big bore kit can be a complex process that requires mechanical skills. If I wasn’t comfortable doing it myself, I would need to budget for professional installation. Understanding the installation requirements helped me plan ahead and avoid any potential pitfalls.

Budget Considerations

The cost of a big bore kit can vary significantly depending on the brand and specifications. I found it helpful to set a budget before diving into my purchase. In addition to the kit itself, I also factored in potential installation costs and any additional components I might need, such as gaskets and new jets.

Researching Brands and Reviews

As I began my search, I made sure to read reviews and gather information about different brands. I sought feedback from fellow riders to understand their experiences with various big bore kits. This research helped me narrow down my options and identify what might work best for my Honda 400Ex.

Final Thoughts

Ultimately, buying a big bore kit for my Honda 400Ex was a significant decision. I wanted to ensure that I was making an informed choice that would enhance my riding experience. By considering the benefits, my riding style, compatibility with other mods, installation, budget, and brand research, I felt confident in my ability to choose the right kit for my needs.

Author Profile

Sandra Tuller

Hi, I’m Sandra Tuler Founder of Tynt Beauty. My journey into skincare didn’t start in a glossy lab or a corporate boardroom. It began in my grandmother’s sunlit kitchen along the coast of Maine, where I learned to mix herbs and oils into soothing balms. Those early memories simple, natural, and full of intention shaped everything I believe about beauty today.

In 2025, I began documenting more of what I’ve learned. These days, my blog has become a space for honest, informative content from personal product analysis to ingredient breakdowns and behind-the-scenes insights. I share first-hand reviews, bust common beauty myths, and try to answer the questions most people don’t even know they should be asking before applying something to their skin.

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