This article will take an in-depth look at engine dynos.
The article will bring more detail on topics such as:
This chapter delves into the fundamentals of engine dynamometers, discussing their structure and the principles behind their operation.
An engine dynamometer is an essential device used for assessing the performance of an internal combustion engine that has been decoupled from its typical environment, such as a vehicle or generator. Its main function is to evaluate engine performance before reinstalling it for its intended purpose.
The use of engine dynamometers can pinpoint issues like overheating, signal faults, or performance inconsistencies, while also testing the quality of new constructions and repairs in a stable environment before practical application.
These dynamometers connect to the engine under evaluation through a drive or cardan shaft, and the engines, positioned on mobile carts, can be smoothly moved into the testing chamber. Typically, these dynos utilize a water brake, electric (EC), or alternating current (AC) system to administer loads.
Despite differences, engine dynos typically share vital elements: a driver or absorption unit, a mechanism for torque generation, and a system for gauging torque and rpm. Normally, the absorber comprises a rotor placed within a housing connected to the testing assembly.
Friction, hydraulic fluids, or electromagnetic forces are common means to create torque. A load cell or strain gauge, or perhaps a scale like a crane scale, often serves as the measuring device. Note: Load cells, also known as load sensors, translate perceived mechanical force into readable signals.
A coupling is a mechanical component used to link the ends of two shafts for power transmission. It connects rotating parts, allowing for small misalignments and movements. More generally, a coupling may refer to a device connecting adjacent components or structures.
Typically, couplings do not allow disconnection of shafts during operation. Torque-limiting couplings, however, are engineered to slip or disengage when the torque surpasses a set threshold. Proper selection, installation, and maintenance of couplings can significantly reduce maintenance time and expenses.
A tachometer is designed to measure an engine's speed in RPM. Mechanical and electronic tachometers operate differently. Within the engine or gearbox, a rotating element connects to the gauge via a flexible cable with a spinning shaft. This turning shaft adjusts a needle to display engine speed.
Electronic tachometers generate electrical pulses with frequencies proportional to engine speed, using a magnetic sensor near a moving engine part. Its circuitry translates these pulses into a digital display indicating the RPM.
The torque arm, part of car suspension, connects to the rear drive axle in rear-wheel-drive vehicles. It supports straight-line acceleration while stabilizing the rear axle.
Besides facilitating braking by transferring force to the brake system, this arm is utilized on engine dynamometers. Connected to a scale, it measures and displays reaction forces.
Absorbing dynamometers simulate loads exerted on the prime mover during testing. They must operate at any specified speed and load, providing the essential torque.
Contrarily, inertia dynamometers gauge power by assessing energy needed to accelerate a known mass drive roller, bypassing a variable load. Engine dynamometers employ absorption units, measuring torque and speed, typically.
The dynamometer's power absorption unit (PAU) captures energy from the prime mover, converting it to heat dissipated into air or cooled water. Regenerative dynamometers enable prime movers to power a DC motor acting as a generator, potentially feeding excess energy back into the grid via a DC/AC inverter.
Different testing demands dictate the use of constant force or constant speed control systems in absorption dynamometers.
In mechanical engineering, trunnion bearings form a part of a rotating connection, providing strength and precision due to their extensive surface contact. These concentric bearings facilitate smooth movement of critical steering components in airframes. The term also refers to wheels supporting rotating components.
A data acquisition system, indispensable in dynamometer setups, typically encompasses two units connected via an Ethernet cable: a commander and a workstation. The commander, a Windows-based desktop computer, instructs the workstation, which manages throttle control and load, collects data, and conveys it for processing and analysis.
The workstation's efficiency, and consequently the data's accuracy, hinge on its ability to measure inputs precisely during tests. Key elements include pressure transducers, which measure fluid pressures like intake manifold and oil pressure. The operator must actively monitor and adjust fluid pressures, demonstrating the workstation's ability to manage pressures effectively.
Engine dynamometers quantify an engine's RPM or flywheel torque to determine horsepower, converting the torque into electrical signals for easy interpretation. These tools facilitate independent engine and vehicle tests, widely employed in engine diagnostics, rebuilding, design, and auto manufacturing.
Select an appropriate dynamometer based on your requirements, ensuring its correct setup before beginning horsepower evaluations. Start with a well-maintained, reliable engine operating at peak capability.
Initially, warm the engine incrementally by applying light loads. Upon adequate warming, apply a full load, adjusting the RPM with the control valve as required.
With the throttle fully open, navigate between RPM test points using the brake’s load valve, documenting results. After measurements, gradually ease the throttle and brake load, returning the engine to idle, completing the initial testing.
Repeating tests is vital for refining accuracy and validating data reliability, ultimately enhancing engine performance and data assurance.
Test data can be saved for later review and adjustment considerations to optimize engine horsepower. Repeated testing may be needed for precise performance tuning.
Several aspects should influence your choice of an engine dynamometer:
Determine if you're assessing stand-alone engines or entire vehicles. For vehicles, consider whether you're working with cars, motorcycles, trucks, or varied types. Consider four-wheel or two-wheel drive dynamometers, and whether an independent or coupled axle setup suits your needs.
Decide if focusing solely on power absorption or addition of motor capability is essential. Selection should be based on horsepower range, budget, and intended test type.
Horsepower reflects torque and RPM correlations over an engine's range. Dynos are evaluated based on torque and RPM as well. Ascertain peak torque and RPM for each engine, along with maximum RPM. Consider engine type (gasoline, diesel) and application (vehicle, industrial, racing) for horsepower predictions.
Develop a testing plan or profile indicating typical horsepower at expected RPMs, plotting a "Horsepower and Torque vs RPM" power curve to identify suitable dynamometer models, each with distinct power curves.
Dynamic testing includes three primary types:
Acceleration tests push engines from lower starting to upper finishing RPM, with deceleration tests reversing the process. Sweep testing, often used to refine performance curves, manages acceleration-deceleration rates.
Steady-state tests hold engines or vehicles at fixed speeds, torques, or power levels, such as step and break-in tests.
Transient or cyclical tests vary speed and load throughout a cycle, with the dynamometer modifying loads to meet goals. Water brake systems adapt these methods but offer slower responses to load shifts, while AC dynamometers, despite inertia, efficiently model coast-down effects.
Cost consideration in dynamometers involves power absorption units besides consistent prices for data acquisition and control systems. AC types, while versatile, are costly, yet enable both energy absorption and engine propulsion for realistic assessments. Costs tie to motor size and ancillary equipment.
Eddy current units, usually water-cooled, function with limited chilled water but their power capability and size directly impact price. Typically spanning 100-500 HP, larger models exist for high-power needs.
More affordable than AC models, water brake dynamometers provide capable power management but necessitate substantial water supplies. Low-power intermittent tests only require moderate water, yet for intense sessions, advanced cooling and water extension increase total costs, aligning water brake pricing with eddy current counterparts.
While water brake absorbers may start at 500 HP, long-duration and high-power tests require factoring the cost of water supply, equaling eddy current systems in overall expenses.
This chapter will explore the different types of engine dynamometers used for automotive testing, engine development, performance tuning, and research within the motorsports and industrial sectors. Understanding each type of engine dyno, their function, and their ideal applications is crucial for selecting the most effective solution, whether you're a performance tuner, automotive engineer, or engine builder.
Eddy current engine dynamometers use an advanced electromagnetic brake to apply a highly controllable load to the test engine, making them popular for precision engine diagnostics and high-performance testing. The core mechanism involves generating a magnetic field in a rotating disc, which creates resistance against the engine's output. This resistance is converted to heat, which is dissipated either into the air or managed through water cooling systems. For lower-power applications (commonly up to 250 horsepower), electromagnetic brakes provide reliable power absorption and are also widely used in chassis dynamometers to test both engines and full vehicles.
Water-cooled electromagnetic (EC) engine dynamometers offer unmatched responsiveness and precise load control, with the ability to vary load from zero to 100% within milliseconds. This makes eddy current dynos a top choice for transient testing, including emissions test cycles and rapid calibration scenarios. However, eddy current systems are typically 40 to 60% more expensive than water brake dynos and offer a more limited dynamic range, which makes them best-suited for specialized engine testing, research and development, and applications where repeatability and fine control outweigh cost considerations.
AC dynamometers are advanced engine and chassis dynos that use variable-frequency AC motors to generate load and, with regenerative power electronics, can return excess electrical power to the grid. This unique regenerative capacity may allow the operator to receive compensation from the local electric utility, depending on grid management policies. AC dynos represent the cutting edge of engine dynamometer technology and are favored for their flexibility, energy efficiency, and ability to replicate real-world driving conditions.
AC dynos excel in dynamic and transient testing due to their rapid response and precision control capabilities. They simulate rapidly changing load conditions an engine would experience in on-road or racing scenarios, including downhill runs, stop-and-go driving, or start-stop city cycles. This technology is available for power ranges from 10 HP to 5,000 HP, fitting both engine dynos and chassis dynos requiring sophisticated transient or road load simulation.
Water brake engine dynamometers utilize water momentum transfer to create resistive load on the test engine. As the engine operates, energy from the engine heats the water by spinning a rotor that forces water through internal passages. Water brake dynos are the preferred choice for high-power engine dyno testing, handling power levels from 350 to an impressive 10,000 HP. Their heavy-duty design is ideal for both internal combustion engines and high-capacity electric motors used in industrial and marine applications. The hydraulic brake system efficiently converts engine output into heat, which is then safely transferred to the circulating water supply.
The assembly consists of a stationary component (stator) and a rotating component (rotor), each with cup-shaped pockets or vanes to maximize water transfer and load absorption. An automated control valve regulates water flow according to specific test parameters, providing dynamic load adjustments and ensuring precise, repeatable measurement of engine torque and horsepower.
Water brake dynos offer the broadest dynamic range, enabling accurate testing across a variety of engine speeds and torque outputs, from low-speed idle to high-rev performance. As the most cost-effective dynamometer technology for high output engines, water brake dynos are widely used in commercial engine shops, OEM powertrain test facilities, and heavy equipment manufacturing. Their durable construction and consistent results make them a staple for engine break-in, validation, and performance benchmarking.
This section will compare engine dynamometers with chassis dynamometers to help users select the right tool for optimizing vehicle and engine performance, meeting regulatory requirements, or improving powertrain efficiency.
An engine dynamometer is a dedicated power measurement tool that assesses engine output by calculating the precise amount of torque needed to maintain a constant rotational speed (RPM). Using sophisticated dynamometer software, it determines engine horsepower with the formula: horsepower = (torque x engine speed) / 5.252. Engine dynos monitor multiple engine health metrics such as water and oil temperature, oil pressure, RPM, exhaust temperature, and air/fuel ratio through linked sensors for accurate, real-time analysis.
Operators benefit from comprehensive control interfaces—ranging from manual cable levers to sophisticated electronic systems—allowing efficient activation and precise management of test procedures. Engines are usually isolated from their accessory drives and may be equipped with custom headers or exhaust systems to facilitate controlled, repeatable testing conditions tailored to specific requirements.
Since engine dynamometers measure torque directly and precisely, they offer the most accurate representation of raw engine performance, making them indispensable for detailed component comparison, fuel mapping, troubleshooting, and maximizing engine output. Other advantages include consistent repeatability, easier parts access, and isolated tuning without influence from drivetrain variables.
Unlike engine dynos, a chassis dynamometer measures the complete drivetrain output as delivered to the vehicle’s drive wheels, providing a holistic measure of vehicle performance “at the wheels.” A typical chassis dyno consists of a platform with rollers, a power absorption (or braking) system, and analytical software for calculating wheel horsepower and torque. In addition to power figures, many modern chassis dynos provide real-time analysis of air/fuel ratios, engine diagnostics, and emissions data, supporting compliance and performance optimization.
Testing involves positioning the driven wheels on the dyno’s drums or rollers. Measurement methodologies vary: some chassis dynos infer torque by assessing the acceleration of rollers (inertia-type), while others use load cells to gauge the force absorbed directly by the braking system (brake-type). The result is an accurate engine power output with drivetrain losses—including transmission, differential, and wheel drag—factored in. For motorsports teams, this enables practical performance tuning that mirrors real-world conditions.
The main advantage of chassis dynamometers is their ability to replicate real-world conditions by measuring horsepower and torque at the wheels—critical for vehicle tuning, drivetrain diagnostics, and validating modifications under actual load. While tuning and part swapping are not as straightforward as on engine dynos due to drivetrain complexity, chassis dynos excel at assessing overall system efficiency and road-ready performance.
To summarize, understanding the differences between engine and chassis dynamometers, as well as the available dyno technologies—eddy current, AC motor, and water brake—empowers users to make informed decisions for their engine testing, tuning, or development needs. The right dynamometer can maximize test accuracy, reduce development time, and ensure compliance with modern vehicle standards.
This chapter will explore the applications, advantages, and maintenance considerations of engine dynos.
The applications of engine dynos are:
Engine dynos provide numerous advantages to users. Primarily, they enable manufacturers to assess the power and performance of their engines and electric motors before these products are launched to the market. By using engine dynos, manufacturers can identify potential inefficiencies or performance problems, such as slow power acceleration or faulty brakes, that could lead to costly issues or operational problems.
By identifying and addressing these issues, manufacturers can make the necessary fine-tuning adjustments to ensure optimal performance and safety. This not only enhances the reliability of their products but also reduces the risk of costly repairs and recalls. Additionally, it allows manufacturers to assure customers of the safety and quality of their engines.
Engine dynos also contribute to the efficiency of engines, leading to better fuel economy and reduced emissions, which benefits the environment. Manufacturers can use engine dynos to ensure their engines meet EPA standards and to promote their environmental credentials.
As engine dynos continue to evolve, they are becoming increasingly automated and advanced. This ongoing development reduces human error and enhances measurement speed and accuracy. The future of engine dynamometers promises further improvements in power, safety, efficiency, and performance for many years to come.
Considerations in engine dynos maintenance are:
To boost productivity, it is essential to service the dyno according to the recommended intervals. Following the manual guide for preventive maintenance is crucial. Additionally, key personnel should receive proper training on both the use and upkeep of the equipment. For on-site support, calibration, evaluation, maintenance, and repairs, Power Test’s technical service staff should be engaged.
Maintaining high water quality is essential for extending the lifespan of a dyno.
Engine dynos can consume over 100 gallons of water per minute. Cool incoming water helps keep the dynamometer cool, allowing it to operate efficiently for longer periods. If recirculated water is used, it should be cooled via a cooling tower before being circulated through the dyno.
Engine dynos have two types of lubrication points: high-speed bearings and trunnion bearings. The lubrication system may use grease or oil depending on the dyno's age. Refer to the owner's manual for proper lubrication procedures.
Vibration sounds may be due to a loose bolt, but they can also signal more significant issues. For example, improper phasing and alignment of a driveshaft can cause vibrations that may damage the driveshaft, dyno, engine, or even pose safety risks if the driveshaft fails.
Engine dynos, also referred to as engine dynamometers, are devices that are used to test an engine’s internal combustion. They calculate the power output by measuring the magnitude of the force (torque) required to hold a spinning engine at a set speed (rpm) directly. There are different types of engine dynos offering different benefits. For example, the water brake dynamometers which provide a wide dynamic range meaning one dyno can test a wide range of engine speeds and engine torques. However, for maximum performance, the engine dyno must be regularly maintained.
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