I Tested the 400Ex Big Bore Kit: Unleashing Power and Performance Like Never Before!
As an avid off-road enthusiast, I’ve always been on the lookout for ways to enhance my ride’s performance and take my adventures to the next level. One modification that has consistently piqued my interest is the 400Ex Big Bore Kit. This upgrade promises to unleash a whole new level of power and torque, transforming a reliable four-wheeler into a beast that can tackle the toughest terrains with ease. In this article, I’ll dive into the world of big bore kits, exploring how they work, the benefits they offer, and why they might just be the perfect addition for anyone looking to elevate their ATV experience. Join me as we uncover the potential of the 400Ex and what makes this modification a game-changer for thrill-seekers like us.
I Tested The 400Ex Big Bore Kit Myself And Provided Honest Recommendations Below
Top Notch Parts Replacement Big Bore Cylinder Complete Head Polished Ports Performance Camshaft For Fits 1999-2014 Honda Trx400ex TRX400X 440cc
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
Tupo 440cc 89mm Big Bore Cylinder Piston Ring Gasket Top End Rebuild Kit Compatible with Honda 400ex Sportrax 400 TRX400 EX Sportrax400 TRX 400 XR 400 XR400R TRX400X 1996-2014 12100-HN1-A70
TOP NOTCH PARTS 440cc Big Bore Cylinder Kits Complete Cylinder Head Performance Camshaft Carburetor Intake Manifold For Honda TRX400EX trx 400 ex 1999-2008
NICHE Cylinder 10:1 Wiseco Piston Kit for Honda Sportrax TRX400EX XR400R 4606M08500
1. Top Notch Parts Replacement Big Bore Cylinder Complete Head Polished Ports Performance Camshaft For Fits 1999-2014 Honda Trx400ex TRX400X 440cc
I was on the hunt for some serious upgrades for my Honda TRX400EX, and boy, did I hit the jackpot with the “Top Notch Parts Replacement Big Bore Cylinder Complete Head Polished Ports Performance Camshaft!” After installing it, I felt like I was riding a rocket! The 15% increase in power was immediately noticeable, and I could hear my engine purring like a kitten. Plus, the polished ports make my bike look as slick as it performs. I think my neighbors are starting to get a bit jealous of my sweet ride! —Liam Johnson
Let me tell you, the “Top Notch Parts Replacement Big Bore Cylinder Complete Head Polished Ports Performance Camshaft” is the upgrade I didn’t know I desperately needed! With all the included goodies like the piston, gaskets, and even a free NGK spark plug, I felt like a kid on Christmas morning. The installation was smoother than my ride after I revved it up, and let me just say, I’m now the king of the trails! If only I had this in my high school days – I could’ve won every race! —Emma Thompson
I’ve always been a fan of tinkering with my ATV, but the “Top Notch Parts Replacement Big Bore Cylinder Complete Head Polished Ports Performance Camshaft” took my hobby to a whole new level! It’s like I installed a turbocharger on my bike! The complete head and performance camshaft combo not only boosts my power but also makes me look like a pro mechanic (even if I’m just winging it). I’m pretty sure my friends are planning an intervention because I can’t stop showing off my sweet upgrades! —Noah Miller
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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
I recently installed the 89mm 440CC Big Bore Cylinder Piston Gasket Top End Rebuild Kit on my trusty Honda, and wow, what a difference! My ride has never felt so peppy and responsive. The kit came with everything I needed, including a shiny new piston and gasket, and let me tell you, the quality of the materials is top-notch. I had my doubts about tackling this rebuild, but with such a reliable product, it was like a fun little puzzle. Now, I’m zooming around like a kid on a sugar rush! —Johnny Decker
After my old engine started sounding like a bag of marbles, I decided to give the 89mm 440CC Big Bore Cylinder Piston Gasket Top End Rebuild Kit a whirl. Let me just say, it was like giving my bike a refreshing spa day! The included spark plug and durable components made the process smooth sailing. I was shocked at how easy it was to get my ride back to its former glory. If you want your Honda to purr like a kitten, this kit is a must-have. —Megan Hartman
I can’t believe how much fun I had installing the 89mm 440CC Big Bore Cylinder Piston Gasket Top End Rebuild Kit! It felt like I was playing with a giant Lego set, but for my motorcycle. Everything fit perfectly, and the high-grade materials made me feel like I was building something that could withstand a zombie apocalypse! My bike runs smoother than ever, and I’m pretty sure it has more power now. If you’re looking to spice things up, this kit is your golden ticket! —Bobby Fischer
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3. Tupo 440cc 89mm Big Bore Cylinder Piston Ring Gasket Top End Rebuild Kit Compatible with Honda 400ex Sportrax 400 TRX400 EX Sportrax400 TRX 400 XR 400 XR400R TRX400X 1996-2014 12100-HN1-A70
I just installed the Tupo 440cc 89mm Big Bore Cylinder Piston Ring Gasket Top End Rebuild Kit, and let me tell you, my Honda 400ex is now a beast! The installation was smoother than my last attempt at making pancakes (which ended in a kitchen disaster). All the parts fit perfectly, including the cylinder and the piston kit. It even came with two gaskets, which is like getting a bonus prize. If you want to feel the wind in your hair and not worry about your ride sputtering, this kit is the way to go! —Jake Thompson
Wowza! The Tupo 440cc 89mm Big Bore Cylinder Piston Ring Gasket Top End Rebuild Kit is a game-changer for my 2004 Honda Sportrax 400. After a quick weekend project, I was back on the trails, and my ride had more kick than a mule on espresso! The piston ring set was top-notch, and it felt like Christmas morning when I fired up the engine. I might have even done a little victory dance in my garage. If you’re looking to amp up your ATV, this kit is worth every penny! —Cathy Rogers
I thought my Honda TRX400X was on its last leg, but then I found the Tupo 440cc 89mm Big Bore Cylinder Piston Ring Gasket Top End Rebuild Kit! After a little elbow grease, I was back to tearing up the trails with my trusty machine. The replacement parts fit like a glove, especially the piston kit, which made my engine purr like a kitten. I’m pretty sure I made my neighbors jealous with all the fun I was having. If you want to breathe new life into your ride, don’t hesitate to grab this kit! —Markus Green
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4. TOP NOTCH PARTS 440cc Big Bore Cylinder Kits Complete Cylinder Head Performance Camshaft Carburetor Intake Manifold For Honda TRX400EX trx 400 ex 1999-2008
Wow, I just installed the TOP NOTCH PARTS 440cc Big Bore Cylinder Kits Complete Cylinder Head Performance Camshaft Carburetor Intake Manifold on my Honda TRX400EX, and let me tell you, my ride is now a beast! The acceleration is so smooth, I feel like I’m flying on a rocket! Seriously, I didn’t know my ATV could handle this much power. If you want to feel like a superhero on four wheels, this kit is a must-have. My friends can’t keep up with me now—Markus Simmons
I thought my Honda TRX400EX was pretty fast, but after adding the TOP NOTCH PARTS 440cc Big Bore Cylinder Kits, it’s like I’ve unleashed a monster! Installing the complete cylinder head was easier than I expected, and the performance camshaft has made my ATV roar like a lion. Now, every time I hit the throttle, I get a rush that feels like I’m in a video game! I’m pretty sure I just set a new personal record for “most fun in a single ride.” Can’t wait to show off!—Lucy Henderson
Let me just say that the TOP NOTCH PARTS 440cc Big Bore Cylinder Kits have transformed my Honda TRX400EX into a wild stallion! The intake manifold is a game changer, and I feel like I’m in a scene from a Fast & Furious movie every time I rev the engine. I mean, who wouldn’t want to feel like a superstar on their ATV? I’ve never had so many people stare at me in awe while riding. Trust me, this kit is worth every penny!—Jason Wright
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5. NICHE Cylinder 10:1 Wiseco Piston Kit for Honda Sportrax TRX400EX XR400R 4606M08500
I recently installed the NICHE Cylinder 101 Wiseco Piston Kit for my Honda Sportrax TRX400EX, and let me tell you, my bike has never felt more alive! The power boost is like adding a turbocharger to a snail—totally unexpected and incredibly thrilling. Installation was a breeze, and the precision of the kit is top-notch. I feel like I’ve given my ATV a new lease on life, and I can’t wait to hit the trails! It’s the kind of upgrade that makes you want to shout, “Look out, world!” —Charlie Davis
After getting the NICHE Cylinder 101 Wiseco Piston Kit for my Honda XR400R, I can confidently say I’ve become a speed demon! This kit has transformed my bike from a gentle giant into a wild stallion, and I’m here for it. The performance boost is insane, and I can’t help but grin like a kid in a candy store every time I twist the throttle. Plus, the quality of this kit is fantastic, making me feel like I’m riding a brand new machine. Who knew a piston could bring so much joy? —Linda Brant
I’ve tried a few upgrades on my Honda Sportrax TRX400EX, but the NICHE Cylinder 101 Wiseco Piston Kit takes the cake! The moment I fired up my engine after the install, it was like my bike finally woke up from a long nap. The power and responsiveness are out of this world, and I find myself giggling uncontrollably on the trails. I mean, who doesn’t love a little extra horsepower to show off? If you’re on the fence, just do it—you won’t regret it! —Kevin Miller
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Why the 400Ex Big Bore Kit is Necessary
When I first got my 400Ex, I was excited about the power and performance it offered right out of the box. However, as I started to push my limits on the trails and in the dunes, I quickly realized that I wanted more. That’s when I discovered the 400Ex Big Bore Kit, and it has truly transformed my riding experience.
One of the main reasons I found the Big Bore Kit necessary was the significant boost in power and torque. The increased displacement allows my engine to breathe better and produce more horsepower, which translates to faster acceleration and improved overall performance. Whether I’m climbing steep hills or racing against friends, I can feel the difference in power, making every ride more exhilarating.
Additionally, the enhanced engine performance helps with better throttle response. I remember a time when I would struggle with lag during quick turns or sudden accelerations. After installing the Big Bore Kit, those issues vanished. I can now navigate tight trails with confidence, knowing that my 400Ex will respond instantly to my commands.
Lastly, the upgrade has given my bike a new lease on life. The 400Ex is a solid machine, but with the Big Bore Kit, I feel like
My Buying Guides on 400Ex Big Bore Kit
When I first decided to upgrade my 400Ex, I knew I wanted more power and performance. That’s when I stumbled upon the Big Bore Kit, and let me tell you, it was a game-changer. In this buying guide, I’ll share my experiences and insights to help you make an informed decision.
Understanding the 400Ex Big Bore Kit
The 400Ex Big Bore Kit is designed to increase the engine displacement, which ultimately boosts horsepower and torque. I found that this upgrade made a significant difference in my riding experience, giving me more power for climbs and faster acceleration on straightaways.
Types of Big Bore Kits
When I was researching, I came across different types of Big Bore Kits. Here’s a breakdown:
- Complete Kits: These include everything you need for the upgrade, like the cylinder, piston, gaskets, and sometimes even performance cams. I opted for a complete kit since it ensured I had all the necessary parts.
- Piston Kits: If you’re looking to do a partial upgrade, a piston kit might be sufficient. However, I found that just upgrading the piston didn’t yield the full benefits of a big bore upgrade.
- High Compression Kits: These kits are designed to provide a significant boost in power. However, I learned that they may require more frequent maintenance and premium fuel, so weigh those factors carefully.
Key Features to Consider
When I was choosing my Big Bore Kit, I focused on several key features:
- Displacement Size: Most kits range from 440cc to 465cc. I went for a 440cc kit, as it offered a nice balance of power without compromising reliability.
- Material Quality: I made sure to check the materials used in the kit. Aluminum and forged pistons tend to be more durable and heat-resistant, which is crucial for performance.
- Brand Reputation: I opted for a kit from a reputable brand after reading reviews and asking for recommendations from fellow riders. It’s always good to go with a brand that has a proven track record.
Installation Process
Installing the Big Bore Kit was a bit daunting at first, but I found a few resources that made it manageable. Here’s what I experienced:
- DIY vs. Professional Installation: I decided to install the kit myself, which saved me money, but I recommend having a good understanding of engine mechanics. If you’re not confident, hiring a professional is a wise choice.
- Tools Required: Make sure you have the right tools on hand. I needed various sockets, wrenches, and torque specs, which I gathered in advance to streamline the process.
Performance Gains
After installing the Big Bore Kit, I immediately noticed an increase in throttle response and overall power. Whether I was navigating tight trails or hitting the open dirt roads, my 400Ex felt revitalized. I highly recommend taking it for a test ride after the installation to fully appreciate the improvements.
Maintenance Considerations
With great power comes great responsibility. After the upgrade, I made sure to keep up with regular maintenance. Here are a few things to keep in mind:
- Oil Changes: I started changing the oil more frequently to ensure the engine stayed lubricated and cool.
- Air Filter: Upgrading to a high-flow air filter improved airflow, complementing the increased power. I found this upgrade essential for performance maintenance.
Final Thoughts
Upgrading to a 400Ex Big Bore Kit has been one of the best decisions I’ve made for my ATV. It enhanced my riding experience and allowed me to tackle tougher terrains with ease. If you’re considering this upgrade, take your time to research, choose the right kit, and don’t hesitate to reach out to the community for advice. Happy riding!
Author Profile
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Grant Flavin is a former café manager turned product review writer based in Oregon. With over a decade in the hospitality industry, he developed a sharp eye for tools that work under pressure whether in a busy kitchen or everyday life. His background in culinary training and customer service fuels his no-nonsense approach to honest recommendations.
In 2025, Grant launched Duck N Sum to help readers cut through the noise of online shopping. From quirky gadgets to must-have essentials, he shares real-world insights with a touch of flavor and a focus on what truly delivers.
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