The Harley-Davidson Milwaukee-8 engine, introduced in 2017, has quickly become a favorite for performance modifications. Since its release, Fuel Moto has been developing and testing big bore engine kits for this motor to meet the growing demand for increased displacement and performance. Understanding the available options and specifications is essential for anyone looking to upgrade their M-8 engine. This guide provides detailed H-D Milwaukee-8 engine and big bore displacement information to help clear up any confusion.
Understanding Stock H-D Milwaukee-8 Engine Bore and Stroke
The Milwaukee-8 engine comes in various displacements, each with unique bore and stroke combinations. These combinations affect the engine’s characteristics and performance. Here are the specifications for stock Milwaukee-8 engines:
H-D Milwaukee-8 107″: 3.937″ bore x 4.375″ stroke
H-D Milwaukee-8 114″: 4.00″ bore x 4.5″ stroke
H-D Milwaukee-8 117″: 4.075″ bore x 4.5″ stroke
These measurements define the engine’s displacement, which is a critical factor in determining horsepower and torque output.
Harley-Davidson SE Stage III and IV Kits
Harley-Davidson’s SE Stage III and IV kits offer performance upgrades by increasing displacement through new bore and stroke combinations. These kits are popular among riders seeking improved power. Below are the options available:
Milwaukee-8 Stage III/IV 114 Kits: 4.075″ bore x 4.375″ stroke
Milwaukee-8 Stage IV 117 Kit: 4.075″ bore x 4.5″ stroke
Milwaukee-8 Stage III/IV 119 Kits: 4.155″ bore x 4.375″ stroke
Milwaukee-8 Stage III 122 Kit: 4.155″ bore x 4.5″ stroke
Milwaukee-8 Stage IV 128 Kit: 4.310″ bore x 4.375″ stroke
Milwaukee-8 Stage IV 131 Kit: 4.310″ bore x 4.5″ stroke
These kits cater to different performance goals, providing riders with flexibility based on their riding style and power preferences.
Aftermarket Big Bore Kits: Expanding Performance Options
For those seeking even more power, aftermarket big bore kits offer significant displacement increases. Depending on your build objectives, you can bore OEM cylinders or replace them with aftermarket options. It’s essential to understand the limitations of factory Milwaukee-8 cylinders:
Milwaukee-8 107″ engines: Factory cylinders can be bored to a maximum of 4.125″ (117 cubic inches).
Milwaukee-8 114/117″ engines: Factory cylinders have a thicker sleeve and can be bored to 4.180″ (124 cubic inches).
Important Note: We no longer bore factory cylinders. Instead, we recommend aftermarket cylinders with thicker liners. These cylinders fit the case spigot without machining and provide the best option for big bore builds up to 131 cubic inches.
Aftermarket Cylinder Options
Here are some popular aftermarket big bore cylinder configurations:
Milwaukee-8 120″ Big Bore for 107 Engines: 4.180″ bore x 4.375″ stroke
Milwaukee-8 124″ Big Bore for 107 Engines: 4.250″ bore x 4.375″ stroke
Milwaukee-8 128″ Big Bore for 114/117 Engines: 4.250″ bore x 4.5″ stroke
These options offer substantial performance improvements, transforming your ride’s power and torque capabilities.
Why Choose Big Bore Kits for Your Milwaukee-8 Engine?
A big bore kit enhances your Milwaukee-8 engine by increasing displacement, which directly boosts power and torque. However, choosing the right setup depends on your specific performance goals. Aftermarket kits offer more flexibility and performance gains than OEM options, making them an excellent choice for those seeking maximum power.
Understanding the H-D Milwaukee-8 engine and big bore displacement ensures you make informed decisions. By selecting the right kit and following proper installation procedures, you’ll unlock impressive power gains and elevate your riding experience.