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The torque converter, a key component of automatic transmissions, has seen a resurgence of interest and development in recent years. This white paper explores the evolution, advantages, and potential applications of the torque converter in modern automotive transmissions. We delve into the historical context, the challenges faced by early torque converters, and how advancements in technology have addressed these issues. With a focus on efficiency, performance, and fuel economy, this paper highlights how the torque converter's return is reshaping the landscape of automotive transmissions.


The torque converter, invented over a century ago, had been overshadowed by various transmission technologies, such as dual-clutch and continuously variable transmissions (CVTs). However, due to advancements in design, materials, and control systems, the torque converter is making a compelling return as an integral part of modern automotive transmissions.

A torque converter is a fluid coupling that transfers rotating power from the engine to the transmission in an automatic vehicle. It is a fluid coupling because it uses the force of fluid to transmit power, rather than gears or a clutch. The torque converter fits between the engine and the transmission, and it performs the same function as a clutch in a manual transmission. When the vehicle is moving, the torque converter allows the engine to be isolated from the load, which means that the engine can continue to run even when the vehicle is stopped. The torque converter is a complex device, but it is an essential part of the automatic transmission. It allows the transmission to shift gears smoothly and efficiently, and it also helps to protect the engine from damage.

Working of Torque Converter

The torque converter finds its position between the internal combustion engine and the gearbox. Within the enclosure of an automatic transmission, three primary components can be identified: the torque converter, the epicyclic (planetary) gearbox, and the electro-hydraulic control module. The crankshaft of the internal combustion engine is mechanically linked to the torque converter. Inside this converter, the engine's power gets transmitted to the gearbox in a hydrodynamic manner. In instances where the torque converter remains unlocked, no direct mechanical linkage exists between the input (engine) and the output (gearbox).

Fig 1: Torque converter construction

The Return of the Torque Converter: Why This Old Technology is Making a Comeback in the Performance Segment


The torque converter inherently possesses an efficiency that tends to be quite modest. This is due to its perpetual slippage, engendering substantial friction between the operational fluid (oil) and the mechanical constituents (impeller, turbine, and stator). The efficiency experiences a nadir, dropping below 10%, when the speed ratio approximates 0 but attains its zenith, ranging from 85% to 90%, when the speed ratio hovers around 0.85.

To augment the efficiency of the torque converter, a strategy is employed whereby when the slippage between the impeller and the turbine remains relatively minimal, the converter is effectively locked. This feat is accomplished using a lock-up clutch, facilitating a mechanical linkage between the impeller and the turbine. Consequently, this arrangement eradicates any further friction between the oil and the components, permitting the engine's power to be transferred mechanically to the gearbox.

Activation of the lock-up state typically ensues in the higher gears (beyond 2nd gear) or when the vehicle's speed surpasses 20 kilometers per hour. During the process of gear shifting, the lock-up clutch is purposefully placed in a slipping mode to contribute to the absorption of driveline oscillations.

Fig 2: Torque converter – lock-up clutch

The Return of the Torque Converter: Why This Old Technology is Making a Comeback in the Performance Segment


The torque converter serves as the primary coupling mechanism in the majority of epicycloidal automatic transmissions (AT), alongside its application in certain continuously variable transmissions (CVT). Its primary attributes encompass the automatic disengagement of the engine from the driveline during low engine speeds, the provision of torque amplification, and the mitigation of vibrations (attributed to the hydrodynamic nature of power transfer).

Data Bridge Market Research analyses the torque converter market will exhibit a CAGR of 5.20% for the forecast period of 2022-2029 and would likely to reach an estimated value of 11.24 billion in the end of the forecast period of 2022-2029.

To know more about the study, visit

History of Automatic Gearbox

The pioneer behind the creation of the inaugural automatic transmission (AT) was Alfred Horner Munro. A native of Regina, Saskatchewan, Canada, Munro formulated the concept of the first automatic transmission in the year 1921, christened the "Automatic Safety Transmission" (AST). This groundbreaking invention was formally granted a patent in the year 1923. Munro, hailing from a professional background as a Canadian steam engineer, harnessed the innovative approach of utilizing air pressure as opposed to hydraulic fluid in the design of the AST. However, this novel approach did present a notable drawback in terms of power generation. Despite this limitation, the AST showcased four distinct forward gear ratios. It is important to note that it lacked both a reverse gear and a parking mechanism. The pioneering invention gained recognition as General Motors introduced the AST into the market, featuring it as an optional upgrade in three of their vehicle models – Oldsmobile, Cadillac, and Buick – during the years 1937 to 1938.

General Motors made a pivotal move by acquiring the prototype and plans, marking a significant stride in automotive history. This heralded the introduction of the inaugural hydraulic transmission, aptly named the "Hydra-Matic." Commencing its production in the year 1940, General Motors offered the Hydra-Matic as an optional feature within the Oldsmobile lineup. This marked a monumental milestone as it stood as the first automatic transmission to undergo mass production, setting a new precedent within the automotive landscape.

The transformative impact of this innovation extended far beyond the automotive realm. In the midst of World War II in 1942, the focus of automotive plants shifted from manufacturing cars to the production of military tanks and vehicles. Remarkably, these military machines were equipped with the Hydra-Matic Transmission, underscoring the adaptability and significance of this technological advancement in various contexts.

In the aftermath of the war, during the post-war era, the demand for vehicles equipped with the Hydra-Matic transmission surged considerably. This was an era characterized by the heightened popularity of this transmission technology. By this juncture, a staggering three-quarters of General Motors' vehicle sales featured the Hydra-Matic option, reinforcing its resounding success and its profound influence on the automotive landscape.

Fig 3: M-5 Stuart tank with Hydra-Matic Transmission

The Return of the Torque Converter: Why This Old Technology is Making a Comeback in the Performance Segment

Source: Auto Service Experts

In 1948, Buick's Dynaflow marked the first hydraulic transmission with a torque converter, boasting two forward gears and reverse. The converter's torque multiplication made the 2-speed setup remarkably potent. Packard introduced the 2-speed Ultramatic in 1949, followed by General Motors' pinnacle achievement, the Power Glide, in 1950. The Power Glide remains a dominant force, still used in top fuel and ¼ mile racing cars, bolstered by modifications for optimal race application.

Fig 4: General Motors Power Glide AT

The Return of the Torque Converter: Why This Old Technology is Making a Comeback in the Performance Segment

Borg Warner made a significant stride by launching the inaugural 3-speed automatic transmission featuring a lock-up torque converter. This breakthrough occurred in the mid-1950s. During this period, a multitude of major automobile manufacturers, including notable names such as Bentley, Lincoln, Ford, and Studebaker, adopted the 3-speed automatic hydraulic transmissions from General Motors as a standard choice.

In the present day, automotive transmissions have evolved to encompass gear trains with as many as 11 speeds. These advanced transmissions integrate an array of sophisticated technologies, including electronic control solenoids, variable speed sensors, and computerized control systems. The Continuously Variable Transmission (CVT) serves as a noteworthy example, characterized by a hydraulic chain-driven configuration that emulates the attributes of an automatic transmission. Moreover, the modern landscape of transmissions includes an assortment of drivetrain configurations, such as front-wheel drive, all-wheel drive, transaxles, transfer cases, and 4x4 transmissions, further reflecting the intricate diversity in automotive engineering.

Fig 5: CVT Transmission

The Return of the Torque Converter: Why This Old Technology is Making a Comeback in the Performance Segment

Data Bridge Market Research analyses that the continuously variable transmission market was valued at USD 19.80 billion in 2021 and is expected to reach USD 31.56 billion by 2029, registering a CAGR of 6.00 % during the forecast period of 2022 to 2029. In addition to the market insights such as market value, growth rate, market segments, geographical coverage, market players, and market scenario, The market report curated by the Data Bridge Market Research team includes in-depth expert analysis, import/export analysis, pricing analysis, production consumption analysis, and pestle analysis.

To know more about the study, visit,

Other Types of Transmissions

Automated Manual Transmission (AMT) represents an automatic transmission system employing an actuator and an onboard computer to discern the appropriate gear shifts based on engine speed. In the case of AMTs, a selector stick is utilized to designate the desired drive mode. Once activated, the driver can simply assume a relaxed driving posture, as the AMT autonomously manages clutch engagement and gear changes. The AMT operation generally delivers a seamless experience, although a slight perceptible jolt might be sensed when the gears transition automatically during both upshifting and downshifting maneuvers.

Fig 6: Automated Manual Transmission – AMT

The Return of the Torque Converter: Why This Old Technology is Making a Comeback in the Performance Segment

Continuously Variable Transmission (CVT) represents a more contemporary iteration of automatic transmissions. Within this transmission variant, gear ratios undergo continuous adjustments contingent upon the vehicle's speed. This adaptability is achieved through a duo of conical pulleys, interconnected by a belt. The belt modifies its diameter by either constricting or expanding based on the requisite gear ratio dictated by factors such as speed, vehicle weight, inclines, and declines. The hallmark of CVT lies in its exceptional efficiency. It strives to uphold a consistent engine revolution per minute (RPM) even as the vehicle traverses an array of speeds. This capacity to seamlessly adapt to varying conditions contributes to the CVT's reputation for optimal efficiency.

Direct Shift Gearbox (DSG) or Dual Clutch Transmission (DCT) is an advanced transmission system that employs two clutches for seamless automatic gear changes. Gears are organized into two groups: odd (1, 3, 5) and even (2, 4, 6), each controlled by a distinct clutch. This configuration effectively mitigates power loss, setting it apart from transmissions such as AMT and manual, as gears remain pre-engaged and swiftly deployable upon achieving the necessary gear revolutions.

The DSG/DCT Transmission distinguishes itself through its refined and efficient performance. This technology finds its application primarily in high-end vehicles, where it delivers a harmonious blend of smooth operation and optimal efficiency.

Benefits of Torque Converter

Disadvantages of Torque Converters

Torque converters, while offering several advantages, also come with certain disadvantages:

Modern Torque Converters

Traditionally, transmissions such as the Powerglide, Turbo 350/400, and C4 have adhered to the conventional non-lockup configuration. In these systems, the converter is engineered as a fluid coupling mechanism, comprising essential components including the turbine, pump, and stator. The initial inception of the lockup-style transmission aimed to enhance overall efficiency. Within this context, a clutch embedded within the torque converter is activated through fluid pressure, a process meticulously regulated by a solenoid.

In the context of older transmissions incorporating the lockup feature, its activation was typically confined to the fourth gear. The mechanism involved locking the converter to the input shaft using clutch engagement, effectively eliminating any potential slip. This intervention yielded tangible benefits such as improved fuel economy and a reduction in transmission temperatures.

However, contemporary advancements have redefined the landscape. Modern transmission models exhibit a significant departure from these traditional methodologies. The implementation of the lockup feature has evolved to an extent where engagement is initiated as early as second gear. Unlike previous iterations, the clutches within these modern units are activated progressively, facilitating efficient coupling of the converter. By the time the vehicle reaches third or fourth gear, the lockup mechanism is fully engaged. This intricate progression renders the hydraulic aspect of the converter virtually obsolete during these later stages of operation.

Multi-disc clutches within torque converters have raised questions about their durability compared to manual transmission clutches. Wet clutches are generally more durable, and proper tuning is crucial for their longevity. Expert tuning can extend clutches' lifespan to match the vehicle's usage. However, excessive applying pressure should be avoided to prevent premature wear and converter distortion. A billet front cover reinforces lockup regions to counteract flexing during the power application.

The choice between multiple or single clutches in converters is determined by engine torque levels. A lockup clutch's capacity depends on factors such as friction coefficient, lockup surface dimensions, piston force, and cone angle. The number of clutch surfaces directly affects torque capacity. Circle-D offers one, three, and five-disc clutch options, allowing users to select the appropriate configuration based on their driving needs. This adaptability ensures optimal converter performance tailored to individual driving demands.

The stator, located at the core of the torque converter, holds a pivotal role in influencing both efficiency and stall speeds. Its design directly impacts these characteristics. Its primary function involves rerouting transmission fluid from the turbine back to the pump, culminating in the multiplication of torque. The progression of technology and advanced manufacturing practices has precipitated notable changes in stator designs over time.

The evolution of stator technology is evident, transitioning from original equipment (OE) stators to the present utilization of fully machined billet stators crafted using five-axis CNC machinery. This transformation has yielded significant performance enhancements. By leveraging various OE options across platforms such as 245mm, 258mm, and 265mm, targeted adjustments can be made to achieve exceptional performance outcomes. This expertise has enabled the refinement of setups over the years. Furthermore, the incorporation of Computational Fluid Dynamics (CFD) within engineering processes has been instrumental in shaping the latest advancements in stator design.

In 2018, Circle-D Specialties, an established player in crafting high-performance torque converters, took a transformative step by integrating Computational Fluid Dynamics (CFD) software. This adoption marked a significant shift, enabling the company to design innovative components and revolutionize its approach.

The introduction of CFD software not only facilitated the creation of products for new transmissions but also empowered Circle-D to reevaluate older units, seeking avenues for improvement. This technology has allowed the design of stators and converters without relying on physical testing in vehicles, a testament to its potential.

While not novel in the industry, CFD software has traditionally been embraced by major automakers such as General Motors and Ford. What's remarkable is its growing adoption by aftermarket entities such as Circle-D, which is leveraging it for virtual tuning. This approach streamlines the development process, reducing research and development costs and accelerating product launches.

By using the software, Circle-D gains insights into pressure distribution, fluid dynamics during converter coupling, and torque multiplication across a range of transmissions, from two-speed to 10-speed.

While primarily used for 10-speed torque converters at the time of this article, Circle-D plans to revisit its entire converter lineup, aiming to optimize torque multiplication through software-driven refinements. The software's potential lies in its ability to provide better control over torque multiplication, facilitating targeted force application and real-time numerical analysis.

This shift away from traditional trial-and-error methods to simulation-driven insights marks a significant progression in the industry, with the potential to be a game-changer. The incorporation of CFD software is poised to provide Circle-D with a competitive edge in advancing torque converter technology.

Fig 7: CFD software

The Return of the Torque Converter: Why This Old Technology is Making a Comeback in the Performance Segment

Source: Power Automedia

Torque Converters in Performance Cars

Exploring the Essential Role of Torque Converters in High-Performance Automatic Transmissions and Their Impact on Acceleration and Driving Enjoyment

Torque converters occupy a crucial role within the realm of automatic transmissions, and their significance is heightened when applied to high-performance vehicles. In the quest for superior acceleration, responsiveness, and an exhilarating driving experience, high-performance cars rely on advanced torque converters to effectively channel engine power to the transmission, ultimately translating into wheel movement.

Understanding the intricate role of torque converters in high-performance transmissions is fundamental to appreciating the technological underpinnings that facilitate these vehicles in delivering captivating driving sensations.

At the core of a torque converter's function lies its capability to enable seamless power transfer from the engine to the transmission. As the engine generates torque, it instigates fluid flow within the torque converter. This fluid motion serves as the conduit for transmitting the rotational force to the transmission, facilitating the vehicle's movement devoid of any jarring or abrupt transitions. In the context of high-performance automobiles, where uninterrupted power delivery is paramount, torque converters play a pivotal role in ensuring a smooth driving encounter, especially during rapid acceleration and gear shifts.

A distinctive advantage of torque converters is their elimination of the need for a conventional manual clutch in automatic transmissions. For high-performance cars, where split-second gear changes are vital for optimal performance, automatic transmissions with torque converters offer swift and precise shifts without necessitating direct driver intervention. This attribute not only enhances convenience but also empowers drivers to concentrate on the driving experience, particularly in scenarios involving high speeds or intense driving conditions.

Torque converters incorporate a stall ratio that dictates the engine's maximum torque output speed when the vehicle is stationary. In the context of high-performance applications, adjusting the stall ratio becomes pivotal in optimizing launch characteristics. Fine-tuning this ratio ensures that the engine attains peak torque precisely when the vehicle commences movement, contributing to expedited acceleration and superior launch performance.

Contemporary high-performance torque converters frequently integrate lock-up clutches. These clutches engage at higher speeds, establishing a mechanical linkage between the engine's crankshaft and the transmission input shaft, effectively mitigating the fluid coupling effect. Upon activation of the lock-up clutch, the torque converter operates akin to a direct mechanical connection between the engine and transmission, curbing power loss and elevating overall efficiency. This proves especially advantageous during sustained high-speed driving, conserving fuel and optimizing power delivery to the wheels.

In demanding driving conditions commonly faced by high-performance vehicles, torque converters serve a vital role in temperature regulation within the transmission system. The circulation of transmission fluid within the torque converter assists in engine cooling and dissipating heat from the transmission itself. This efficient cooling mechanism plays a pivotal role in averting overheating, and sustaining consistent performance, particularly during intense driving circumstances such as track sessions or spirited driving across challenging terrains. By preserving ideal operating temperatures, torque converters contribute to the transmission's durability and reliability, extending its lifespan and maintaining peak performance over extended durations.

Torque converters afford a degree of adaptability in gear ratios, in contrast to manual transmissions. This adaptiveness empowers high-performance vehicles to excel across a broad spectrum of driving conditions. Whether it's swift acceleration from a standstill or seamless cruising at high speeds, torque converters allow the transmission to optimize gear selection to match the desired driving outcome.

Certain high-performance vehicles harness the potential of torque converters within launch control systems. Launch control optimizes acceleration from a stationary position by regulating engine power and wheel slip. By managing torque delivery during launch, the torque converter ensures efficient traction acquisition, facilitating impressive acceleration metrics and heightening launch consistency.

While torque converters are conventionally associated with traditional automatic transmissions, they also assume a role in dual-clutch transmissions (DCTs). In specific DCT configurations, torque converters are integrated to enhance low-speed drivability and comfort. This hybrid approach amalgamates the smoothness and user-friendliness linked with torque converters, along with the swift gear changes and efficiency of DCTs. As a result, high-performance vehicles equipped with DCTs can harness the advantages of both worlds.

Modern Cars With Torque Converters

The new M3 is being offered in the UK armed with the ZF 8HP torque-converter automatic, which is now in its third generation and has been steadily developed since its introduction in 2009. Strip away all the internal mechanical differences and the key distinction between it (or any torque-converter-based transmission) and a DCT or manual is that the torque is transmitted from the engine to the gearsets by a fluid coupling, the torque converter, rather than by a clutch or clutches

Similarly, Mercedes-AMG C63 S, Porsche 911 Carrera S, and Jaguar F-Type R have also adopted the torque converter transmission and this shows that many of the disadvantages and issues of the torque converters have been tackled with and will see a rise in the adoption.


In conclusion, the resurgence of the torque converter in the realm of performance automobiles marks a remarkable paradigm shift in the automotive industry. This white paper has delved into the multifaceted reasons behind the resurgence of this seemingly archaic technology and has illuminated the nuanced advantages it offers in the context of modern performance vehicles. The torque converter's ability to strike an unparalleled balance between power delivery, smoothness, and efficiency has captured the attention of engineers and enthusiasts alike.

As performance demands continue to evolve, the torque converter has proven its adaptability by seamlessly integrating with hybrid and electrified powertrains, further solidifying its relevance in the ever-changing automotive landscape. Its revival is not just a tribute to tradition, but a testament to the spirit of innovation that drives the industry forward.

The torque converter's renaissance underscores the fact that innovation doesn't always require the abandonment of proven technologies. Instead, it highlights the wisdom of reimagining and refining existing solutions to meet contemporary challenges. The confluence of cutting-edge engineering and the timeless principles of torque conversion has paved the way for a new era of exhilarating, efficient, and sophisticated performance vehicles.

As automakers continue to experiment with innovative transmission designs, the torque converter's revival serves as a reminder that the past can provide valuable insights for the future. Its comeback in the performance segment is a triumphant narrative of how history and progress can intertwine, shaping a driving experience that embraces both tradition and innovation. In the end, the torque converter's return stands as a compelling case study of how old technologies, when reinvigorated with modern ingenuity, can carve out a prominent niche in the pursuit of automotive excellence.

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