The Honda Grom is a compact 125cc motorcycle known for its light frame, fuel efficiency, and fun ride. One of the most asked questions by new and experienced riders is simple: how much horsepower does it have? In this article, you’ll learn the exact horsepower of the Honda Grom and how it affects performance. You’ll also discover five proven modifications that can safely increase its power. Each upgrade is simple, popular, and tested. Whether you’re riding for fun or looking for more speed, this guide will help you understand the Grom’s full potential.
Honda Grom Horsepower: The Basics
The Honda Grom uses a 124cc air-cooled, single-cylinder engine. It comes with a four-speed manual transmission. The most recent models, including the 2022 and 2023 versions, produce around 9.7 horsepower at 7,250 RPM. This is the official figure shared by Honda. Earlier versions, such as the 2014–2020 Groms, produce slightly less—about 9.5 horsepower.
While this number may seem low, it fits the Grom’s lightweight design. The bike weighs only about 225 pounds (102 kg). This low weight helps make the most of its horsepower. The power-to-weight ratio offers enough speed for city roads and short-distance travel.
In real use, the Grom can reach a top speed of 55 to 60 mph. With a few upgrades, it may reach up to 70 mph, depending on rider weight and road conditions. The bike’s power delivery is smooth and predictable, making it ideal for beginners and casual riders.
Why HP Matters on a Grom
Horsepower plays a key role in how a motorcycle performs. For small bikes like the Honda Grom, even a small change in horsepower can make a big difference in speed and ride quality. The engine size is small, so power is limited. But that also means each extra unit of horsepower adds real performance.
The Grom is not built for racing or highways. Its power is focused on low-speed control and smooth riding. This makes it easy to handle in traffic and in narrow spaces. Still, many riders want more acceleration or higher top speed. That’s where horsepower becomes important.
Extra horsepower helps in quick take-offs from stops. It can also improve uphill climbs and passing power on open roads. Even a gain of one or two horsepower is noticeable on a bike this small. Riders who use their Grom daily or for fun rides often choose to boost HP for a better riding experience.
5 Easy Mods to Boost Honda Grom HP
Modifying the Honda Grom to increase horsepower is popular among riders. These five upgrades are beginner-friendly, cost-effective, and proven to improve engine output. Each mod works by improving airflow, fuel delivery, or engine efficiency.
1. Aftermarket Exhaust System
A performance exhaust replaces the stock exhaust with a lighter, more open design. This allows gases to leave the engine faster. Better exhaust flow helps the engine breathe and produce more power. Some exhausts also reduce weight. A typical gain is 0.5 to 1 horsepower, depending on the brand and design. It also changes the sound, making the bike louder and deeper.
2. High-Flow Air Intake/Filter
A high-flow air filter increases the amount of clean air that enters the engine. More air means better fuel burn, which leads to stronger power output. This upgrade is simple to install. It works well with an exhaust system. Together, they create a balanced air-in and air-out setup. The result is a small but noticeable performance improvement.
3. ECU Flash or Fuel Controller
The Engine Control Unit (ECU) controls how fuel and air are used. A stock ECU is set for emissions and fuel efficiency. Flashing the ECU or adding a fuel controller allows better tuning for performance. This adjusts how much fuel enters the engine at different speeds. It unlocks the full benefit of other mods. Gains depend on setup, but it’s often the most effective mod.
4. Big Bore Kit
This upgrade increases engine size by replacing the cylinder and piston. A larger engine burns more fuel and air, which increases horsepower. Big bore kits are more complex to install but deliver strong results. Power can rise by 2 to 4 horsepower, depending on the kit. This is ideal for riders who want a big change in speed and acceleration.
5. Performance Camshaft
The camshaft controls when the engine valves open and close. A performance camshaft changes this timing for better airflow. This helps the engine pull harder at higher speeds. It adds mid to high RPM power, which improves speed. This upgrade works best when paired with other mods like the ECU flash or big bore kit.
How Much HP Can You Expect After Mods?
The stock Honda Grom produces around 9.7 horsepower. After adding performance upgrades, this number can increase. Each modification adds a small amount. Together, they create a noticeable change.
An aftermarket exhaust and high-flow air filter may add around 0.5 to 1 HP. With a fuel controller or ECU flash, gains increase to about 1.5 HP in total. These three upgrades are often done together for balanced results.
Adding a big bore kit raises power by 2 to 4 HP, depending on the size and setup. With the right tuning, the engine can reach over 13 horsepower. A performance camshaft adds another 0.5 to 1.5 HP, especially in the higher RPM range.
When all five mods are combined and tuned correctly, riders can expect a total output of 13 to 15 horsepower. This is a significant improvement over stock. It improves acceleration, throttle response, and top speed. However, actual results may vary based on rider weight, elevation, and tuning quality.
Dyno testing gives the most accurate result. Many riders share real dyno charts online after installing mods. These tests confirm the performance increase with real numbers.
Is It Worth It? (Cost vs. Gain)
Upgrading the Honda Grom for more horsepower costs money. Each modification adds to the total price. Some upgrades are affordable. Others require a bigger investment. Riders must balance performance with budget.
A high-flow air filter costs around $30 to $60. It is easy to install and lasts long. An aftermarket exhaust system ranges from $150 to $400, depending on the brand. A fuel controller or ECU flash costs between $100 and $250, based on the model and features.
A big bore kit is the most expensive. Prices start at $200 and can go beyond $400. It also requires installation skills or a mechanic. A performance camshaft usually costs $100 to $200. Some riders also pay extra for tuning or dyno testing, which can cost another $100 to $200.
Adding all five mods may cost $600 to $1,200 in total. The final price depends on brands, tools, and labor. For many riders, this price is fair for the improved power and riding feel. Others may prefer to keep the Grom stock for lower cost and less maintenance.
Before upgrading, riders should set clear goals. If the goal is more speed and fun, the upgrades are worth it. If the goal is simple, everyday use, fewer mods may be enough.
Conclusion
The Honda Grom is a small motorcycle with a simple engine and lightweight frame. Its stock horsepower is around 9.7 HP, which fits its size and design. For many riders, this is enough for daily use and short rides.
For those who want more power, there are five proven upgrades: a performance exhaust, high-flow air filter, ECU flash or fuel controller, big bore kit, and performance camshaft. Each mod adds more horsepower and better throttle response. When combined, these changes can raise the Grom’s power to 13–15 HP.
Mod costs vary. Some are budget-friendly. Others require tools and experience. Riders must decide based on how much power they need and how much they want to spend.
Understanding horsepower helps riders get the best from their Grom. Whether you keep it stock or upgrade it fully, the goal is the same—make the ride more enjoyable.
FAQs
What is the top speed of a stock Honda Grom?
The top speed of a stock Honda Grom is about 55 to 60 mph. It may vary slightly depending on the rider’s weight and road slope.
Does increasing HP affect fuel efficiency?
Yes. More horsepower can reduce fuel economy, especially with larger upgrades like a big bore kit. However, small mods like a new air filter or exhaust have less impact.
Will performance upgrades void the warranty?
Some upgrades may affect the factory warranty. Always check the owner’s manual or ask a Honda dealer before making changes.
