Honda TRX400EX / XR400R 440cc Big Bore Kit - 89mm 10:1 Piston + Complete Gasket Kit (1996-2016)
Breathe New Life Into Your Honda — 440cc of Reliable, Affordable Power
Stop leaving power on the table with a stock 400cc cylinder. This complete 440cc big bore kit from 50 Caliber Racing bolts directly onto all Honda TRX400EX, TRX400X, and XR400R models from 1996–2016. The 89mm cylinder features an improved design with a larger sleeve for longer-lasting performance, paired with a hard anodized 10:1 piston dome for improved compression and throttle response. Everything you need is in the box — no hunting for separate parts. If you can turn a wrench, you can install this kit.
What’s in the Box
Why Riders Upgrade
Big Bore Kit vs. Stock Options
✗ Less torque across the RPM range
✗ Potential for increased wear if pushed hard
✗ Requires engine rebuild for similar gains
✓ Increased torque & throttle response
✓ 10:1 Compression on Pump Gas
✓ Hard anodized piston for durability
✓ Bolt-on installation
Common Questions
What is a big bore kit and how does it work?
A big bore kit increases your engine's displacement by using a larger cylinder and piston. This allows for more air and fuel to enter the combustion chamber, resulting in more power and torque.
Do I need to machine my engine to install this kit?
No, this kit is designed as a direct bolt-on upgrade and requires no machining. It installs using basic mechanical skills.
Will this kit work with my specific Honda model and year?
This kit is compatible with all Honda TRX400EX, TRX400X, and XR400R models from 1996 to 2016.
Can I use regular pump gas with this kit?
Yes, the 10:1 compression ratio is optimized to run on standard pump gas without detonation.
What Riders Are Saying
Installed this on my TRX400EX in an afternoon. The difference in throttle response is immediately noticeable. Kit had everything I needed and the instructions were clear.
— John D., California
My XR400R had a tired top end. This kit brought it back to life and then some. Bolt-on as advertised — no machining, no surprises.
— Mark T., Texas
Ready to Unlock More Power?
In Stock Now - Join thousands of Honda owners who trust R1 Industries for reliable, affordable performance upgrades.
Stop riding a tired 400. 440cc bolt-on kit, complete with everything — more power, same reliability.
Vehicle Fitment
Honda TRX400EX — 1996-2016Honda TRX400X — 1996-2016
Honda XR400R — 1996-2003
Original: $59.49
-65%$59.49
$20.82Product Information
Product Information
Shipping & Returns
Shipping & Returns
Description
Breathe New Life Into Your Honda — 440cc of Reliable, Affordable Power
Stop leaving power on the table with a stock 400cc cylinder. This complete 440cc big bore kit from 50 Caliber Racing bolts directly onto all Honda TRX400EX, TRX400X, and XR400R models from 1996–2016. The 89mm cylinder features an improved design with a larger sleeve for longer-lasting performance, paired with a hard anodized 10:1 piston dome for improved compression and throttle response. Everything you need is in the box — no hunting for separate parts. If you can turn a wrench, you can install this kit.
What’s in the Box
Why Riders Upgrade
Big Bore Kit vs. Stock Options
✗ Less torque across the RPM range
✗ Potential for increased wear if pushed hard
✗ Requires engine rebuild for similar gains
✓ Increased torque & throttle response
✓ 10:1 Compression on Pump Gas
✓ Hard anodized piston for durability
✓ Bolt-on installation
Common Questions
What is a big bore kit and how does it work?
A big bore kit increases your engine's displacement by using a larger cylinder and piston. This allows for more air and fuel to enter the combustion chamber, resulting in more power and torque.
Do I need to machine my engine to install this kit?
No, this kit is designed as a direct bolt-on upgrade and requires no machining. It installs using basic mechanical skills.
Will this kit work with my specific Honda model and year?
This kit is compatible with all Honda TRX400EX, TRX400X, and XR400R models from 1996 to 2016.
Can I use regular pump gas with this kit?
Yes, the 10:1 compression ratio is optimized to run on standard pump gas without detonation.
What Riders Are Saying
Installed this on my TRX400EX in an afternoon. The difference in throttle response is immediately noticeable. Kit had everything I needed and the instructions were clear.
— John D., California
My XR400R had a tired top end. This kit brought it back to life and then some. Bolt-on as advertised — no machining, no surprises.
— Mark T., Texas
Ready to Unlock More Power?
In Stock Now - Join thousands of Honda owners who trust R1 Industries for reliable, affordable performance upgrades.
Stop riding a tired 400. 440cc bolt-on kit, complete with everything — more power, same reliability.
Vehicle Fitment
Honda TRX400EX — 1996-2016Honda TRX400X — 1996-2016
Honda XR400R — 1996-2003
