How Much Horsepower Do You Lose From Flywheel to Prop?

When it comes to the world of aviation, the transfer of power from the engine to the propeller plays a crucial role in determining the overall performance and efficiency of an aircraft. One particular aspect that often comes into consideration is the loss of horsepower during this transfer, known as the flywheel to prop loss. This phenomenon refers to the power that’s consumed or dissipated in the process of converting the rotational motion of the engine's flywheel into the thrust required to propel the aircraft forward. Understanding and estimating this power loss is essential for pilots, engineers, and aviation enthusiasts alike, as it directly impacts the aircraft's speed, acceleration, and overall flight characteristics. By unraveling the intricacies behind the horsepower loss from the flywheel to the prop, we can gain a deeper insight into the dynamics of aviation and appreciate the meticulous efforts taken to optimize the performance of these marvelous flying machines.

What Is Prop Shaft Horsepower?

Prop shaft horsepower, also known as shaft horsepower, is a crucial indicator of an engines true power output. This measurement takes into account the power lost to gears and bearings in the transmission system.

When an engine operates, some power is lost due to friction and mechanical inefficiencies in the drivetrain. Gears and bearings play a significant role in transferring power from the engine to the propeller, but they also introduce some resistance and losses. By measuring shaft horsepower, one can assess the actual power that reaches the propeller and is ultimately responsible for propelling the vessel.

For gas and diesel inboards, it’s estimated that the maximum shaft horsepower is around 97 percent of the maximum bhp. This means that only a fraction of the engines total power is effectively transmitted to the propeller. It’s essential to consider this when selecting an engine for a particular vessel, as the prop shaft horsepower determines the boats overall performance and efficiency.

By taking into account the power losses in the transmission system, they can accurately estimate the engines performance and ensure it matches the vessels requirements.

Furthermore, prop shaft horsepower can serve as a benchmark for evaluating the efficiency of the drivetrain components. By comparing the bhp and shaft horsepower values, engineers can identify potential mechanical issues or inefficiencies in the transmission system. This information can guide them in optimizing the drivetrain design to maximize power delivery.

When it comes to measuring the horsepower loss from the crank to the wheels, a formula is often used to convert wheel horsepower (WHP) to engine horsepower (hp). This formula takes into account the drive train loss, which varies depending on the type of drivetrain. For front-wheel drive vehicles, the drive train loss is typically 10%, while rear-wheel drive vehicles experience a loss of 15%. All-wheel drive vehicles tend to see the highest loss, usually around 25%. By understanding these percentages, it becomes possible to accurately assess the true power output of an engine.

How Much Horsepower Loss From Crank to Wheels?

One of the frequently asked questions among car enthusiasts and mechanics is how much horsepower is lost from the engine to the wheels. This loss is often referred to as drivetrain loss or powertrain loss, and it varies depending on the type of drivetrain a vehicle has.

To calculate the engine horsepower (hp) from the wheel horsepower (WHP), a formula is used. The formula takes into account the drivetrain loss, which is different for front-wheel drive, rear-wheel drive, and all-wheel drive vehicles.

For front-wheel drive vehicles, the drivetrain loss is typically around 10% or 0.This means that 10% of the engines power is lost in the transmission, differential, and other components before it reaches the wheels. So, if you’ve a car with 200 WHP, the engine horsepower would be 200 divided by 0.90, resulting in approximately 222 hp.

This is due to the additional components required to transfer power to the rear wheels.

All-wheel drive vehicles have the highest drivetrain loss among the three types, typically around 25% or 0.2The additional components including the transfer case and differentials contribute to this higher loss.

It’s important to note that these values are approximate and can vary depending on various factors like vehicle condition, weather conditions, and individual vehicle setup. Additionally, it’s worth mentioning that drivetrain loss can also be affected by modifications such as aftermarket exhaust systems, performance tunes, or changes to the drivetrain components themselves.

Understanding the horsepower loss from crank to wheels is crucial for accurately gauging a vehicles true performance potential. This knowledge enables enthusiasts and mechanics to make informed decisions when it comes to modifications and tuning for optimal power and performance.

Source: WHP to HP Calculator

The distinction between brake horsepower and flywheel horsepower lies in their measurements and considerations. While brake horsepower solely evaluates the power at the flywheel, overlooking power loss during energy transfer, flywheel horsepower encompasses the complete power output and subsequent losses. Although occasionally referred to as flywheel horsepower, this terminology remains less prevalent.

What Is the Difference Between Brake Horsepower and Flywheel Horsepower?

On the other hand, flywheel horsepower is a more accurate representation of the actual power being transferred to the wheels of the vehicle. It takes into account any power losses that occur in the transmission, drivetrain, and various mechanical components of the vehicle. Flywheel horsepower is typically lower than brake horsepower due to these power losses.

The power losses in the drivetrain and mechanical components can significantly affect the performance and efficiency of the vehicle.

Brake horsepower is often used in marketing and promotional materials for vehicles, as it represents the maximum power that the engine can produce.

Understanding this difference is crucial when assessing the true performance and efficiency of a vehicle.

What Are Power Losses in the Drivetrain and Mechanical Components and How Do They Affect Vehicle Performance?

Power losses in the drivetrain and mechanical components refer to the energy that’s consumed or dissipated as heat during the transfer of power from the engine to the wheels of a vehicle. These losses can occur in various parts of the drivetrain, such as the transmission, differential, and bearings, as well as in other mechanical components.

The presence of power losses negatively impacts vehicle performance in several ways. Firstly, it reduces the overall efficiency of the vehicle, meaning that less power from the engine is effectively translated into forward motion. This leads to decreased fuel efficiency and higher energy consumption.

Secondly, power losses can affect acceleration and top speed. As energy is wasted in the drivetrain, less power is available to propel the vehicle. This results in slower acceleration and a lower maximum speed capability.

Furthermore, power losses generate heat, which can cause components to overheat and potentially fail. This can lead to decreased reliability and increased maintenance costs.

To optimize performance, manufacturers strive to minimize power losses in the drivetrain and mechanical components through various means, such as the use of efficient lubricants, improved bearing designs, and advanced transmission technologies. By reducing power losses, vehicles can achieve better fuel efficiency, enhanced acceleration, and improved overall performance.

When it comes to measuring horsepower, there’s often a discrepancy between the numbers obtained at the engine and those transmitted to the rear wheels. Typically, the wheel horsepower will be lower than the engine horsepower, typically varying between 20% to 45%. So, let’s delve deeper into understanding why this power loss occurs and the factors that contribute to it.

How Much Horsepower Do You Lose to the Rear Wheels?

When it comes to automotive performance, enthusiasts often find themselves discussing the amount of horsepower that actually makes it to the rear wheels. This figure, known as wheel horsepower, is often lower than the raw horsepower produced by the engine.

Another factor that contributes to the difference in horsepower is the type of drivetrain. In many modern vehicles, power is sent to the wheels through an automatic transmission. Automatic transmissions tend to have higher power losses compared to manual transmissions, as they utilize torque converters and fluid clutches. These components introduce additional energy losses, further reducing the power delivered to the wheels.

Additionally, factors such as tire grip and rolling resistance play a role in the loss of horsepower to the rear wheels. Tires are responsible for transmitting the power from the drivetrain to the road surface. However, various forces such as tire deformation and rolling resistance can absorb some of this power, resulting in a decrease in wheel horsepower.

It’s also important to consider the efficiency of the engine itself. Engine horsepower is usually measured at the crankshaft, before power is lost due to various mechanical and thermal inefficiencies. These losses can occur in the combustion process, cooling system, and exhaust system, among others.

While it’s difficult to provide an exact percentage, it’s common to experience a reduction of around 20% to 45% in horsepower by the time it reaches the rear wheels. This knowledge is crucial for automotive enthusiasts and professionals alike, as it helps set realistic expectations for performance and allows for more accurate measurements when testing and tuning vehicles.

The Effects of Modifications on Wheel Horsepower

Modifications to a vehicle can have a significant impact on it’s wheel horsepower without compromising the stability and safety of the vehicle. By implementing changes to the exhaust system, air intake, engine components, and fuel management, enthusiasts can enhance the performance of their car. However, it’s important to note that modifications should be done carefully and within legal limits to ensure optimal results.


In conclusion, it’s evident that the power loss from the flywheel to the propeller in terms of horsepower is a complex and multi-faceted phenomenon. Factors such as mechanical efficiency, aerodynamic losses, and transmission losses all come into play, making it challenging to provide a specific numerical value for the power loss. It’s crucial for engineers and designers to carefully account for these losses in the design and operational considerations of aircraft and other applications where power transfer is involved. By continuously seeking improvements in mechanical efficiency, minimizing aerodynamic losses, and optimizing transmission systems, we can strive to mitigate the loss of horsepower from the flywheel to the propeller, resulting in more efficient and effective propulsion systems for the future.

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