Top 7 Harley 103 Engine Performance Upgrades To Get More Power Out Of 103 Harley Davidson

One of the commonly asked questions among Harley owners is “what are the top Harley 103 engine performance upgrades.”

If you are looking for how to squeeze out more power from your Harley, there are several techniques or methods that you can adopt. However, most of these methods are expensive, which a lot of people can’t afford.

Here is the good news. There are affordable and effective methods that you can consider, ensuring you find a way around enhancing your engine’s performance without spending heavily or being in debt.

As you read along, you will find out about the various modifications or adjustments that can be made on your bike without the need for an expert skillset. Also, you won’t have to break the bank.

Basically, these modifications ensure essential parts and components function efficiently and optimally on your motorcycle, thereby guaranteeing a performance upgrade.

Harley 103 Engine Features

  • Electronic Sequential Port Fuel Injection
  • Four-Point Engine Isolation System
  • Compression Ratio 9.6:1
  • Displacement 103 cu. in. (1690 cc)
  • Valves Pushrod-operated
  • Overhead valves with hydraulic
  • Self-adjusting lifters
  • 2 (two) valves per cylinder
  • Lively throttle reaction
  • Air cleaner trim ring
  • Automatic compression release
  • Black powder-coated heads and cylinders
  • Powerful torque
  • Lower cruising rpm
  • Improved highway fuel economy
  • Reduced engine vibration
  • Lightweight piston design
  • Six-Speed Cruise Drive®

HP of Harley 103 Engine

The factory horsepower rating of the Harley 103 engine is about 64hp, and it is measured at about 5000 RPM.

When you ride your motorcycle on lower RPMs, which is the common practice, the HP falls between 45 and 55 Horsepower.

If the Harley 103 engine is modified using the stage 1 kit. This adjustment increases the horsepower to about 75 HP and 90 ft torque.

How fast can the Harley 103 engine go?

On average, Harley motorcycles have a top speed of about 115 mph. This is quite impressive when you consider the average time it takes (4.3 seconds) to move from 0 mph to 60 mph.

While the Harley 103 engine is built to supply enough power your bike needs, modifications increase the horsepower and ensure you get more power out of your motorcycle.

Why do you need to upgrade 103 Engine?

An individual may upgrade the 103 engine whenever they desire more from their motorcycle.

Basically, an upgrade optimizes the engine, ensuring it meets a rider’s performance expectations or requirements.

For instance, If you like to get your heart pumping by riding or touring on the highway.

You may need to enhance your bike’s ability to deliver on your riding needs if you feel that the engine isn’t giving enough power.

If you own or drive a Harley, especially if you are a customization enthusiast, upgrades or modifications are inevitable.

The desire to enhance performance and get additional power out of your motorcycle is always irresistible.


  • Oil filter wrench
  • Oil catch pan
  • Hex keys
  • Torque wrench
  • Socket wrench set
  • O-ring and oil seal puller
  • Oil fluid extractor
  • Oil filter removal
  • Flat and Phillips head screwdrivers
  • Snap-on torque wrench

How to Do Harley 103 Engine Performance Upgrades in a Less Expensive Way

Are you looking for the easiest and less costly way to get more power from your engine? The following methods explain some of the techniques or methods you can adopt or try out.

01. Consider increasing your Harley’s air intake

Your motorcycle’s air intake system is somewhat restricted or suppressed from the factory.

So, an attempt to lower or lift the restriction can be very helpful in enhancing the engine’s combustion.

A simple installation of high-flow air filters plus an increase in the air intake’s surface area improves air intake to a great volume.

The reduction of restriction in the air intake is the easiest and least expensive technique you can adopt to increase your bike’s power and performance.

Usually, an increase or improvement in airflow may result in a rise in fuel consumption. Hence, the need to find the right balance in the air-fuel mixture ratio.

A good consideration is to tune your bike’s carburetor accordingly.

While adjusting or upgrading your air filters with necessary add-ons, especially if you decide to use a complete air box removal kit.

Ensure you choose a kit that doesn’t leave the filters exposed.

On average, filters cost about $80, and complete airbox removal kits cost about $400. Nevertheless, this is still an easy and quite affordable method.

02. Exhaust system upgrade

This modification complements the first method on our list (air filter upgrade). For a better outcome, ensure you adjust/modify both the intake and exhaust systems.

Since manufacturers have to meet up or adhere to emission requirements at low costs.

The ability of the stock exhaust manifold to move air efficiently is somewhat compromised, thereby restricting performance.

This is where the aftermarket exhaust systems come in. They are designed to provide additional power and torque for increased performance in your bike’s engine almost immediately.

Thanks to their lighter weight and ability to expel/release trapped exhaust gases more efficiently.

The exhaust system upgrade is a very popular and widely adopted bolt-on modification technique.

Asides from increasing your engine’s torque and power, a new exhaust system improves your bike’s appearance and sound.

While the sip-on exhausts are great, investing in a full exhaust system is a better and advanced option.

Although a slip-on exhaust gets the job done by adding extra power to your engine. Usually, the change or modification is experienced only at the lower end.

If you decide to invest in a full exhaust system. Ensure you choose a design that is specifically designed for your motorcycle.

Also, do not forget to install a new aftermarket tuner for improved fuel mapping.

On average, a slip-on exhaust may cost between $250 and $400. If you are considering a full system exhaust, this costs between $600 and $1000 on average.

03. Cylinders upgrade

There are two common techniques that you can adopt to boost or enhance your engine’s cylinders.

This includes boring out existing or installed cylinders or replacing the cylinders and pistons with larger designs.

Once the cylinders are modified or adjusted, the engine’s displacement is enhanced, thereby providing major power and performance boost to your engine.

The process of boring engine cylinders is a bit technical. If you know nothing about engine building or do not have the skills and experience required to rebuild an engine, this is not something you should attempt on your own.

You will need to consult an expert to get the job done for you.

On average, cylinder boring may cost between $60 and $80 per hole.

04. Electronic Control Module (ECU) upgrade or re-flash

The ECU controls several aspects of your motorcycle’s performance. This computer chip is programmed from the factory to comply or meet the industry’s emissions and fuel requirements, restricting the engine from attaining its maximum potential.

The good news is that the ECU can be re-flashed or reset for performance upgrades.

The process of re-flashing the Electronic Control Model involves replacing the stock onboard programming using an improved and more efficient tune.

This modification enhances power gains by unlocking the maximum potential of your Harley’s engine, thereby increasing the ride experience.

If the ECU re-flash is done incorrectly, it will affect your bike’s overall performance. So, consult a qualified mechanic to perform this modification.

The cost of modifying or re-flashing the ECU varies widely. On average, you may spend between $300 and $600 to get the job done.

05. Tuning your carburetor

This is another easy and efficient technique that you can adopt to upgrade your engine’s performance.

Considering the constant change in emission laws and how stringent these laws are, manufacturers faced continuous pressure to comply with the set standards.

As a result, the carburetor is restricted from operating at its maximum potential from the factory. Installing a simple jet kit is all you need to put things right.

For best performance and power output, go for a jet kit compatible with your exhaust and airbox adjustments or upgrades.

The jet kit can be added or installed on both stock and modified motorcycles. When a jet skit is added to a stock motorcycle, the power gains will be minimal. However, the fuel delivery is improved greatly.

The installation on a modified motorcycle gives the best result, and it makes tuning easier.

The cost of a jet kit varies. It depends majorly on the application. On average, the price of a jet kit is between $100 and $300.

06. Using performance headers

Performance headers are definitely one of the easiest bolt-on components that you can install on your bike.

They deliver a modest amount of power, thereby enhancing your engine’s performance.

Performance headers allow your motorcycle’s engine to eliminate exhaust gases from the cylinders easily.

The installation of performance headers is easy, and no special tools are needed.

The price of performance headers varies. It depends mainly on factors such as the number of cylinders in the engine and the style & design of the headers.

Performance headers could cost as low as $200 and as high as $1000.

07. Ignition modification

While looking for an inexpensive, easier, and efficient method of improving engine performance, the ignition is often ignored.

Clearly, the ignition system is a possible source of additional power.

Before you modify your ignition system, you need to conduct the necessary research and findings to make the right decision.

You need to confirm if your engine set up and ignition condition can support the essential changes required to uncork additional power.

Take your time and read through your motorcycle manufacturer’s instructions and recommendations

When successfully done, ignition modification guarantees an improved ignition response time and enhances throttle response.

Benefits of Upgrading 103 engine

  • Combustion becomes more efficient
  • Guarantees consistent performance and increase in mileage
  • Increases motorcycle power and torque
  • Improves sound quality
  • Exhaust gases are expelled more efficiently
  • Smooth riding experience

The problems of upgrade

  • When not done correctly, the bike’s overall performance is affected
  • Increased consumption of fuel

FAQ’s Harley 103 Engine Performance Upgrades

How can I get the best from my motorcycle?

First, you need to understand your preferred riding style. To get the best from your bike, make sure it matches your riding style. Also, have a clear understanding of your performance expectations.

This allows you to make the appropriate modifications or adjustments on the bike to get your desired results.

How do fuel filters improve engine performance?

Just as the name implies, this component filters the fuel and makes it cleaner before entering the engine.

When you use high-quality filters on your bike and replace them regularly, this guarantees efficient and consistent combustion, power, and performance.

How long will a 103 Harley engine last?

The 103 Harley engine is very reliable. Just like every mechanical component or part, the 103 engine is not free from issues.

The good part is that these issues are minor and can be fixed quickly with the appropriate tools, skills, and experience.

When properly used, serviced, and maintained. The Harley 103 engine can last over 150,000 miles.

In between this period, you may have to get the compensator replaced once or twice.

How hard is it to upgrade a Harley engine?

With the right tools, skills, and experience, the process of upgrading your Harley engine is easy.

Before you begin the project, wear your safety gear. Also, ensure you have your bike and space properly cleaned.

What are the least expensive engine performance upgrade methods?

If you are looking for an easier and affordable way of achieving improved or additional power and performance in your engine.

Choose any of the methods that allow a large volume of air-fuel mixture through your bike’s engine.

What amount of increase is attainable after an engine upgrade?

After the adjustments and modifications to the intake and exhaust systems, jet kit, carburetor, and ECU, an increase between 15% and 20% in horsepower are achievable.

This is a really impressive result for individuals who seek easy, affordable, and efficient methods.


When you look at the methods or techniques discussed in this guide. It is evident that the Harley 103 engine performance upgrades are what Harley riders and owners can perform using simple tools and with basic mechanical skills.

When rightly done, your engine achieves an impressive increase in power (20%) and torque (10%) for less than $1000.