How to Make a Lawn Mower Go 40 MPH

Screenshot 395 How to Make a Lawn Mower Go 40 MPH

If you’re looking to transform your lawn mower into a speed machine, you’ve come to the right place. In this article, we’ll explore how to make a lawn mower go 40 MPH by modifying the engine, transmission, tires, and body. We’ll also discuss additional performance enhancements, safety considerations, and maintenance, so you can enjoy your high-speed lawn mowing experience without any accidents.

Understanding Lawn Mower Speeds

Before we dive into modifying your lawn mower, it’s important to understand the factors that affect its speed and what its stock speed is.

Factors Affecting Lawn Mower Speed

Several factors determine the speed of a lawn mower, including:

  • Engine power
  • Transmission type
  • Tire size and type
  • Mower body design

Stock Lawn Mower Speeds

Most lawn mowers have a top speed of around 5 to 8 MPH, depending on the model and type. With modifications, however, you can significantly increase this speed to meet your desired goal of 40 MPH.

Modifying Your Lawn Mower

Here are some ways to modify your lawn mower to achieve a top speed of 40 MPH:

Upgrading the Engine

Screenshot 397 How to Make a Lawn Mower Go 40 MPH

The first step is to increase the engine’s power. This can be done by:

  1. Swapping the stock engine with a more powerful one, such as a small motorcycle or go-kart engine
  2. Installing a turbocharger or supercharger
  3. Modifying the carburetor to allow more fuel and air to enter the engine

Performance Air Filters

Replacing your lawn mower’s stock air filter with a high-performance air filter can help improve air flow and increase engine power. Look for washable, reusable filters that are designed to allow more air to pass through while still trapping dirt and debris.

Tuning Your Engine

Properly tuning your engine can optimize its performance and help you achieve higher speeds. This might involve adjusting the carburetor, ignition timing, or valve clearances. If you’re not experienced with engine tuning, consider consulting a professional for guidance.

Tweaking the Transmission

Screenshot 396 How to Make a Lawn Mower Go 40 MPH

Adjusting the transmission can also increase your lawn mower’s speed. Consider these modifications:

  1. Swap out the stock pulleys with larger ones to increase the drive ratio
  2. Modify or replace the transmission to allow for higher gear ratios
  3. Install a CVT (continuously variable transmission) for smoother, more efficient power delivery

Transaxle Modifications

Altering the transaxle can help improve the gear ratio and increase speed. This might involve swapping out the internal gears or replacing the entire transaxle with one designed for higher speeds.

Chain Drive Systems

Converting your lawn mower’s drive system to a chain drive can help improve efficiency and increase top speed. A chain drive system can be more durable and handle higher speeds better than a belt-driven system.

Altering the Tires and Wheels

Changing the tires and wheels can help you achieve higher speeds by reducing rolling resistance and improving traction. Try these modifications:

  • Use larger, wider tires for better grip
  • Opt for low-profile tires to reduce rolling resistance
  • Install lightweight wheels to decrease unsprung weight

Tire Pressure Adjustments

Proper tire pressure can affect the rolling resistance and overall performance of your lawn mower. Experiment with different tire pressures to find the optimal balance between grip and rolling resistance for your specific setup.

Wheel Spacers

Adding wheel spacers can help improve stability and handling at high speeds by increasing the track width of your lawn mower. This can lead to better cornering ability and more stable straight-line performance.

Streamlining the Mower Body

To minimize air resistance and increase speed, consider these changes to your mower’s body:

  1. Remove any unnecessary parts or accessories
  2. Install a custom aerodynamic body kit
  3. Lower the mower’s ride height to reduce its center of gravity and improve handling

Front Spoilers

Adding a front spoiler can help reduce air resistance by directing airflow around the mower and reducing lift at high speeds. This can lead to better stability and handling.

Rear Wings

Installing a rear wing can help create downforce, which can improve traction and handling at high speeds. The wing should be adjustable, allowing you to fine-tune the downforce level to suit your specific setup and driving conditions.

Additional Performance Enhancements

Screenshot 398 How to Make a Lawn Mower Go 40 MPHIn addition to the modifications listed above, consider these additional performance enhancements to further improve your lawn mower’s speed and handling:

Upgraded Fuel System

Upgrading your fuel system can help ensure that your engine receives the optimal amount of fuel for maximum performance. This might involve installing a high-flow fuel pump, performance fuel injectors, or a custom fuel management system.

High-Performance Exhaust

A high-performance exhaust system can help improve engine power by reducing back pressure and improving exhaust gas flow. Look for an exhaust system designed specifically for your mower’s engine, or consider having a custom system fabricated.

Advanced Suspension Systems

Upgrading your lawn mower’s suspension system can improve handling and stability at high speeds. This might involve installing stiffer springs, performance shock absorbers, or adjustable coilovers to fine-tune your mower’s suspension characteristics.

Safety Considerations

When making modifications to achieve a 40 MPH lawn mower, it’s crucial to keep safety in mind.

Braking and Handling

Ensure that your lawn mower has adequate brakes and can handle the increased speed. You may need to upgrade the brakes to a more robust system, such as disc brakes, and improve the suspension for better stability.

Protective Gear

With the increased speed, it’s important to wear appropriate protective gear, such as a helmet, gloves, and goggles, to ensure your safety while operating your high-speed lawn mower.

Regular Maintenance

Maintaining your lawn mower is crucial, especially when it’s modified for high-speed operation. Regularly inspect and maintain all critical components, such as the engine, transmission, brakes, and suspension, to ensure they are in optimal condition and functioning properly. Keep an eye out for any signs of wear or potential failure, and address them promptly.


Transforming your lawn mower into a 40 MPH machine is an exciting project, but it requires careful planning, attention to safety, and ongoing maintenance. By upgrading the engine, tweaking the transmission, altering the tires and wheels, streamlining the mower body, and incorporating additional performance enhancements, you can create a lawn mower that goes 40 MPH. Always consider the safety implications of these modifications, wear the necessary protective gear, and perform regular maintenance to keep your high-speed mower running smoothly and safely.


How fast can a modified lawn mower go?

With the right modifications, a lawn mower can reach speeds of up to 40 MPH or even higher. However, it’s essential to consider safety and handling when making these modifications.

Can I use a modified lawn mower for racing?

Yes, lawn mower racing is a popular sport, and many racers modify their mowers to achieve high speeds. Make sure to follow the rules and safety regulations of the racing organization you participate in.

Is it legal to modify a lawn mower for increased speed?

Laws and regulations regarding lawn mower modifications vary by location. Always check your local laws and consult with a professional before making any modifications.

Do I need a special license to operate a modified, high-speed lawn mower?

In most cases, you don’t need a special license to operate a modified lawn mower. However, if you plan to use it on public roads or participate in lawn mower races, you may need to obtain a permit or license, depending on your location.

Can I still use my modified lawn mower for regular lawn mowing tasks?

It’s possible to use a modified lawn mower for regular lawn mowing tasks, but it may not be practical due to the increased speed and handling capabilities. Always operate your lawn mower at a safe speed for the task at hand.

How much will it cost to modify my lawn mower to reach 40 MPH?

The cost of modifying a lawn mower to reach 40 MPH can vary widely, depending on the specific modifications you choose and whether you perform the work yourself or hire a professional. It could range from a few hundred to several thousand dollars.

Are there any pre-built lawn mowers available that can reach 40 MPH?

There may be some custom-built or specialty lawn mowers available that can reach 40 MPH, but they are likely to be expensive and not as common as standard lawn mowers. Most people interested in high-speed lawn mowers opt to modify their existing mowers.

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