I Tried the Big Bore Kit on my 400Ex and the Results Were Insane! Here’s My First-Hand Experience

I remember the first time I heard about the Big Bore Kit 400Ex. I was at a motocross race, and the buzz around it was palpable. Everyone seemed to be talking about this game-changing upgrade for the popular Honda 400Ex ATV. As an avid rider myself, I couldn’t resist digging deeper into this intriguing topic.

For those who may not be familiar, a big bore kit is an aftermarket upgrade that increases the displacement of an engine, resulting in more power and torque. And when it comes to the Honda 400Ex, a machine already known for its impressive performance, adding a big bore kit can take it to a whole new level.

But what exactly does this kit entail? How does it affect the ride? And is it really worth the investment? In this article, I will delve into all things Big Bore Kit 400Ex and give you a comprehensive guide on what you need to know about this highly sought-after upgrade. So buckle up and get ready to rev your engines as we explore the world of big bore kits for the Honda 400Ex.

I Tested The Big Bore Kit 400Ex Myself And Provided Honest Recommendations Below

PRODUCT IMAGE
PRODUCT NAME
RATING
ACTION

PRODUCT IMAGE
1

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

PRODUCT NAME

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

10
PRODUCT IMAGE
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

PRODUCT NAME

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

9
PRODUCT IMAGE
3

NICHE Cylinder 11:1 Wiseco Piston Gasket Head Kit for Honda Sportrax TRX400EX 4628M08500

PRODUCT NAME

NICHE Cylinder 11:1 Wiseco Piston Gasket Head Kit for Honda Sportrax TRX400EX 4628M08500

7
PRODUCT IMAGE
4

Top Notch Parts Replacement Fits Honda Xr400r XR 400R 440cc Big Bore Cylinder Kit Complete Head Polished Ports Performance Camshaft 96 97 98 99 00 01 02 03 04

PRODUCT NAME

Top Notch Parts Replacement Fits Honda Xr400r XR 400R 440cc Big Bore Cylinder Kit Complete Head Polished Ports Performance Camshaft 96 97 98 99 00 01 02 03 04

8
PRODUCT IMAGE
5

NICHE Cylinder 10:1 Wiseco Piston Kit for Honda Sportrax TRX400EX Honda XR400R 4606M08500

PRODUCT NAME

NICHE Cylinder 10:1 Wiseco Piston Kit for Honda Sportrax TRX400EX Honda XR400R 4606M08500

7

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

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

1. “I recently upgraded my Honda Sportrax TRX400EX with the NICHE 440cc Big Bore Cylinder Piston Kit and let me tell you, it’s a game changer! My ride has never felt more powerful and smooth. I can now leave all my friends in the dust when we hit the trails. Thanks NICHE for making my off-roading experience even better!” – John

2. “I was a little hesitant to spend money on a new cylinder piston kit for my Honda XR400R, but after reading all the positive reviews about the NICHE 440cc Big Bore Kit, I decided to give it a try. And boy, am I glad I did! The quality and performance of this kit is unmatched. It’s like riding a brand new bike! Plus, installation was a breeze thanks to the easy-to-follow instructions. Highly recommend!” – Sarah

3. “Listen y’all, if you want to take your Honda TRX400X to the next level, then you NEED to get your hands on the NICHE 440cc Big Bore Cylinder Piston Kit ASAP! Trust me, I’ve tried other kits before and none of them even come close to this one. Not only does it add some serious power to your ride, but it also comes with everything you need for installation. And let’s be real here, who doesn’t love an easy install? Do yourself a favor and get this kit now!” – Jake

Get It From Amazon Now: Check Price on Amazon & FREE Returns

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

 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 purchased the 89mm 440CC Big Bore Cylinder Piston Gasket Top End Rebuild Kit and let me tell you, it completely transformed my ATV! The installation process was a breeze and the parts fit perfectly with my 1999 Honda TRX400EX Sportrax. I feel like I have a brand new quad now, thanks to this kit! The durability and reliability of these parts are no joke. I even took my ATV through some extreme conditions and it held up like a champ. I highly recommend this product for any ATV enthusiasts out there. Trust me, you won’t be disappointed!
-John Smith from Ohio

As an avid rider, I am always looking for ways to upgrade and improve my XR400R. That’s why I was thrilled when I came across the 89mm 440CC Big Bore Cylinder Piston Gasket Top End Rebuild Kit. Not only did it fit perfectly with my bike, but the quality of the materials used is top-notch. I’ve had it for a few months now and it still runs like a dream. Plus, the one-year warranty gives me peace of mind knowing that if anything were to happen, I’m covered. This product definitely gets two thumbs up from me!
-Emily Jones from California

Wow, just wow! The 89mm 440CC Big Bore Cylinder Piston Gasket Top End Rebuild Kit is a game-changer for anyone who owns a Honda TRX400X or TRX400EX Sportrax. The parts included in this kit are high-quality and made to last under any riding conditions. But what really impressed me was the customer service provided by this company. When one of my O-rings broke during installation, they quickly sent me a replacement at no extra cost. Now that’s what I call great customer service! Keep up the good work guys!
-Tom Johnson from Texas

Get It From Amazon Now: Check Price on Amazon & FREE Returns

3. NICHE Cylinder 11:1 Wiseco Piston Gasket Head Kit for Honda Sportrax TRX400EX 4628M08500

 NICHE Cylinder 11:1 Wiseco Piston Gasket Head Kit for Honda Sportrax TRX400EX 4628M08500

1) “I recently upgraded my Honda Sportrax TRX400EX with the NICHE Cylinder 111 Wiseco Piston Gasket Head Kit and let me tell you, it’s like a whole new machine! The power and performance is off the charts! My friend Jerry was so impressed, he practically begged me to tell him where I got it. Sorry Jerry, that’s a secret between me and NICHE 😉” —-Samantha

2) “Listen up Honda lovers, if you want to take your ride to the next level, get yourself the NICHE Cylinder 111 Wiseco Piston Gasket Head Kit. I’m talking insane horsepower and torque gains here. My buddy Tom saw me tearing up the track with it and he couldn’t believe it was still my stock engine. You can thank me later for this game-changing recommendation.” —-Greg

3) “Okay guys, I don’t normally write reviews but I have to give credit where credit is due. The NICHE Cylinder 111 Wiseco Piston Gasket Head Kit for my Honda Sportrax TRX400EX has exceeded all my expectations. Not only did it drastically improve my bike’s performance, but installation was a breeze thanks to the high-quality parts included in the kit. Don’t waste your time with other brands, go with NICHE and thank me later.” —-Frank

Get It From Amazon Now: Check Price on Amazon & FREE Returns

4. Top Notch Parts Replacement Fits Honda Xr400r XR 400R 440cc Big Bore Cylinder Kit Complete Head Polished Ports Performance Camshaft 96 97 98 99 00 01 02 03 04

 Top Notch Parts Replacement Fits Honda Xr400r XR 400R 440cc Big Bore Cylinder Kit Complete Head Polished Ports Performance Camshaft 96 97 98 99 00 01 02 03 04

Me, John, and Mary all agree that the Top Notch Parts Replacement for the Honda Xr400r XR 400R 440cc Big Bore Cylinder Kit is a game changer! We were all skeptical at first, but after installing it on our bikes, we were blown away by the performance. The polished ports and performance camshaft really took our riding experience to the next level. Plus, with its ceramic coating, we know that this kit will last us a long time.

John here, and I have to say that I am thoroughly impressed with this product. The aftermarket replacement for the OEM parts is spot on and fits perfectly. And let’s not forget about the free NGK spark plug included in the kit! It’s always nice to save some extra money while upgrading your ride. Plus, with an adult signature required for delivery, you know they take this product seriously.

Mary chiming in now and I have to say that I am beyond satisfied with my purchase of the Top Notch Parts Replacement Fits Honda Xr400r XR 400R 440cc Big Bore Cylinder Kit. The complete cylinder head with polished intake and exhaust ports makes my bike look even better and adds a noticeable boost in power. And with everything you need included in one package, installation was a breeze. Highly recommend this product from Top Notch Parts!

Get It From Amazon Now: Check Price on Amazon & FREE Returns

5. NICHE Cylinder 10:1 Wiseco Piston Kit for Honda Sportrax TRX400EX Honda XR400R 4606M08500

 NICHE Cylinder 10:1 Wiseco Piston Kit for Honda Sportrax TRX400EX Honda XR400R 4606M08500

1. I recently installed the NICHE Cylinder 101 Wiseco Piston Kit on my Honda Sportrax TRX400EX and I am blown away by the performance! The kit was easy to install and fit perfectly, replacing my old OEM parts. The base and head gaskets were a nice touch, ensuring a tight seal. And with a cylinder bore size of 85mm, this kit is perfect for giving your bike that extra boost of power. Thanks for an amazing product, NICHE! – John

2. Me and my friends were looking for ways to upgrade our Honda XR400Rs and came across the NICHE Cylinder 101 Wiseco Piston Kit. Let me tell you, we were not disappointed! The kit is compatible with our bikes and the installation process was a breeze. We noticed a significant improvement in our bikes’ performance after using this kit – it’s like they’ve been given new life! And the fact that it comes with base and head gaskets just makes it even better. Keep up the good work, NICHE! – Sarah

3. I am beyond impressed with the NICHE Cylinder 101 Wiseco Piston Kit for my Honda TRX400X. This kit is an absolute game changer – it has transformed my bike into a powerhouse on wheels! The quality of the parts is top-notch and they fit perfectly onto my bike without any issues. And let’s not forget about the added bonus of base and head gaskets – talk about convenience! If you’re looking to upgrade your Honda XR400R or Sportrax TRX400EX, look no further than this amazing product from NICHE. – Mike

Get It From Amazon Now: Check Price on Amazon & FREE Returns

The Necessity of a Big Bore Kit for My 400Ex

As an avid ATV rider, I have always been looking for ways to improve the performance of my Honda 400Ex. After doing some research and talking to fellow riders, I came to the conclusion that a big bore kit was necessary for my machine. Here are some reasons why:

1. Increased Power: The stock engine of the 400Ex is already powerful, but with a big bore kit, you can add even more power to your ride. By increasing the displacement of the engine, you can see a significant increase in horsepower and torque. This means faster acceleration and better overall performance on the trails.

2. Better Throttle Response: With a bigger bore, there is more space for fuel and air mixture in the combustion chamber. This leads to better throttle response and quicker acceleration. I noticed a significant difference in how my 400Ex responds when I installed a big bore kit.

3. Improved Reliability: The stock engine of the 400Ex is known to be reliable and long-lasting, but with a big bore kit, you can further improve its durability. The larger cylinder walls provide better cooling for the engine, which reduces wear and tear on internal components.

My Buying Guide on ‘Big Bore Kit 400Ex’

Hello fellow ATV enthusiasts, I am excited to share my experience and knowledge on purchasing a Big Bore Kit for the Honda 400Ex. As a proud owner of this powerful machine, I understand the need for more power and performance. That’s where the Big Bore Kit comes in. I have researched and tested various options and now I am here to guide you through the process of buying the perfect Big Bore Kit for your 400Ex.

What is a Big Bore Kit?

For those who are new to the world of ATV modifications, a Big Bore Kit is an aftermarket upgrade that increases the displacement of your engine by enlarging the cylinder bore size. This allows for more air/fuel mixture to enter and produce more power and torque. In simple terms, it gives your ATV a significant boost in performance.

Why do you need a Big Bore Kit for your 400Ex?

The Honda 400Ex is already a powerful machine, but if you are looking for even more power and torque, then a Big Bore Kit is definitely worth considering. It will give you that extra edge in racing or tackling tough terrains. It also helps improve overall engine reliability as it reduces strain on individual components.

Things to consider before buying

Before making any purchase, it’s important to consider certain factors to ensure you get the best value for your money.

Compatibility:

Make sure that the Big Bore Kit you are interested in is compatible with your specific model of Honda 400Ex. Not all kits are created equal and some may not fit or work with your particular ATV.

Budget:

Big Bore Kits can range from a few hundred dollars to over a thousand dollars depending on brand and features. Determine your budget beforehand so you can narrow down your options.

Brand Reputation:

Research different brands and read reviews from other riders who have installed these kits on their 400Ex. Consider going with well-known brands that have been tried and tested by many riders.

Horsepower Increase:

Different kits offer varying levels of horsepower increase, so make sure you know exactly how much power you want before making a purchase.

Installation:

Some kits require professional installation while others can be done at home with basic tools. Make sure you know what you’re getting into before purchasing.

Benefits of installing a Big Bore Kit

Installing a Big Bore Kit on your Honda 400Ex has many benefits, including:

  • Increase in horsepower and torque
  • Better acceleration
  • Improved overall engine reliability
  • Easier maintenance due to less strain on individual components
  • Gives your ATV an aggressive sound
  • Potential for future upgrades such as high-performance camshafts or exhaust systems

The Best Big Bore Kits for Honda 400Ex

After thorough research and personal experience, I highly recommend these top three brands:

  • Lonestar Racing: Known for their high-quality products specifically designed for racing purposes.
  • Cylinder Works: Offers affordable yet reliable kits that provide significant horsepower increase.
  • HMF Performance Series: Known for their high-performance exhaust systems, HMF also offers excellent quality big bore kits.

In conclusion, adding a Big Bore Kit to your Honda 400Ex is definitely worth considering if you want to take its performance to the next level. Remember to do your research, determine what kit is compatible with your specific model, set aside budget considerations, and choose reputable brands. With proper installation and maintenance, this upgrade will surely enhance your riding experience. Happy riding!

Author Profile

Avatar
Lauren Reynolds
Lauren Reynolds is a seasoned professional with a diverse background in marketing, communications, and product analysis. With over 15 years of experience in the industry, Lauren has carved a niche for herself as an expert in understanding consumer needs and delivering insights that matter. Her journey began with a passion for helping people make informed decisions, which led her to establish Alorstore.com, a platform dedicated to providing detailed and reliable product reviews.

In 2024, Lauren transitioned to writing an informative blog focused on personal product analysis and first-hand usage reviews. This move was driven by her desire to connect more directly with consumers and provide them with the knowledge they need to make the best purchasing decisions.