Torque Converter Drives: The Technology That’s Changing Drag Racing

Automatics vs. Manuals: it’s the long-standing debate that rages between drag racers with two very different schools of thought — those who object to automatic transmissions as power-robbing and less-tunable; and the others who condemn manual transmissions for their heavy clutch maintenance. But what if you could have the best of both worlds?

The Great Debate: Automatics Versus Manuals

In virtually all modern vehicles, a coupling device is used to separate the engine and transmission to allow internal-combustion engines to run continually when in use (although a few modern street cars now shut off the engine at stoplights). In manual transmissions, this coupling is accomplished via a clutch, while a torque converter handles the coupling in automatic transmissions. Without it, the engine and tires would at all times be linked, and any time the vehicle is stopped, the engine would stall or shut off as a result. Additionally, changing gears would be extremely difficult, even when the vehicle is moving already: deselecting a gear while the transmission is under load requires considerable force and risks significant damage to the drivetrain assembly.

A Bruno's converter drive mated to a Liberty Extreme 4-speed transmission in the DD/AT turbocharged Cobalt campaigned in Competition Eliminator by Bruno Massel, Jr.

A Bruno’s converter drive mated to a Liberty Extreme 4-speed transmission in the DD/AT turbocharged Cobalt campaigned in Competition Eliminator by Bruno Massel, Jr.

In drag racing, the winning transmission of choice has traditionally been the clutch and manual gear box set up. However, recent automatic transmission technology advancements over the past decade have evened the playing field of performance capabilities compared to the traditional manual transmission counterpart. While manual transmissions create minimal rotating mass and slippage compared to an automatic, the chief complaint for any drag racer lies in the amount of maintenance required round-by-round and inconsistencies in performance associated with clutch adjustment and wear in manuals.

Inversely, this is one area that automatic transmissions shine. The lack of frequent maintenance and their consistency appeal to racers who don’t have the time or crew assistance to handle burdensome clutch maintenance. Nevermind that clutch discs and related parts add up to considerable expense (one racer shared with us that they spent $15,000 annually on clutch discs — a number that’s now at $0 with their converter drive setup). What they save in convenience, their downfalls have traditionally been the power loss attributed to rotating mass and their lack of adjustments.

A new Quick Drive unit installed in Clint Satterfield's NHRA Pro Modified entry.

A new Quick Drive unit installed in Clint Satterfield’s NHRA Pro Modified entry.

Enter The Converter Drive

To capitalize on the benefits of both worlds, a component called the converter drive was developed that would allow racers the ability to use a torque converter for ease of maintenance, while still using a manual gear box for ratio selection and durability. Currently, there are a few major companies in the United States designing converter drive devices, including Brunos Automotive, Lenco, and Quick Drive. Though similar, each company has a different approach to achieving the same goal: combining the benefits of a manual with the ease of maintenance of an automatic.

Bruno Massel, Sr. is largely credited with the early development of the converter drive. Armed with a billet prototype, Massel won Super Comp at the 1989 NHRA Supernationals with the unit in his car. Massel had designed the setup for personal use at the time to allow him to get away from the broken Powerglide transmissions that had hindered his racing endeavors. After being featured in National Dragster, demand became evident and Massel put his his creation into production.

A Quick Lock in the 1970.5 Camaro of Russell Wullenwaber that will be run in the Pro Stock class of the National Hot Rod Diesel Association.

A Quick Lock in the 1970.5 Camaro of Russell Wullenwaber that will be run in the Pro Stock class of the National Hot Rod Diesel Association.

The new converter drive took the ease of automatic transmission torque converter maintenance and combined it with the durability of a manual gear box.

As many already know, a torque converter is basically a type of fluid coupling device (or pump) that is used to transfer rotating power from an engine to a rotating driven load. The torque converter, located between the engine’s flexplate and transmission input shaft, takes the place of a mechanical-style clutch in a vehicle with an automatic transmission, allowing the load to be separated from the power source. The key trait of a torque converter is its ability to multiply torque when there is a substantial difference between input and output rotational speed, thus providing the equivalent of a reduction.

Some torque converters are also equipped with a temporary locking mechanism (lock-up converter) which rigidly binds the engine to the transmission when their speeds are nearly equal, to avoid slippage and a resulting loss of efficiency. A converter drive unit allows you to mate the converter to any manual transmission on the market with various sized input shaft designs, depending on your application.


A Bruno’s Automotive lock-up converter drive unit. The reservoir seen at left contains pressurized oil for operation of the lock-up feature of the converter, while the solenoid activates the reservoir. The black solenoid on the right side of the unit is for activating the transbrake. Bruno’s utilizes an air-operated transbrake system, as it has more holding power and a quicker, more consistent release than a hydraulic transbrake.

 Converter Drive Installation Basics

The unit input shaft (male spline), the inner-most shaft, slips into the converter through the stator hub and mates into the spline (female) on the turbine. The Stator shaft, also part of the drive unit, is hollow and has a male spline on the outside. This is around the input shaft with clearance to allow return fluid to flow from the converter back into the drive unit. This stator shaft mates into the stator of the converter.

The last component that creates the coupling between drive unit and converter is the converter snout — it’s affixed to the converter and is larger than the stator shaft and input shaft. It seals into the drive unit and mates into the drive unit pump gear. This entire coupling is held in place when the drive unit is bolted to the bellhousing. The bellhousing is, of course, bolted to the back of the engine. The converter is bolted to the flexplate, which is bolted to the end of the crankshaft.

It sounds much more complicated when explained in this fashion, but it’s simply three shafts that are slid inside each other between the converter and drive unit.


A Quick Drive Converter Drive unit inside John Stanleys’ PDRA Pro Extreme Cadillac CTS-V. The Stanley & Weiss team made the switch from a clutch to the converter drive combination this season and cut their between-round driveline maintenance down to virtually nothing.

Weight Variances

Quick Drive’s non-lockup unit weighs 45 pounds with no fluid in it. You will also need to take into consideration the weight of the converter, as well. A converter is about 28-38 pounds empty and, on average, a unit with a converter takes about eight quarts of fluid. The standard Bruno’s units weigh about 17 pounds more than the Quick Drive, with the larger pan and the additional fluid. Typically, if you were already running an automatic, then a converter drive would add a little weight.

Racers say with the design of the unit, you’ll never notice any added friction from the rotating assembly. Quick Drive shares that many racers have told them that typically a clutch-style transmission setup weighs a little more than its automatic counterpart, but the weight was not noticeable enough to make a switch back.

A Quick Drive unit and a B&J transmission that are being paired to go in the nitro-burning, front engine A/Fuel Dragster of Wayne Ramay.

Ease of Maintenance

Maintenance? Well, there isn’t much. As far as maintenance goes, fluid is the only thing that needs changed. The converter setup has a lot to do with the maintenance schedule. A looser set-up tends to create fluid shear, more temperature, and requires more frequent fluid change, according to Quick Drive.

Converter Drive System Operation – Bruno

During development and in the years since, Bruno’s designed the now-commonplace 1.25-inch Marage input shaft, working extensively with torque converter manufacturers to develop the standard. Their drives were also the first to implement converter pressure manipulation to assist turbocharged customers in spooling up on the starting line.

non lockup brt

A Bruno non-lock-up converter drive. The pan under the units contains only a filter. “The reason all of our components are on the outside is so that it can be repaired or checked if there is ever an issue, without working in hot oil or removing the transmission from the car,” Bruno Massel, Jr. explains.

Bruno’s converter drive system allows pressures in the converter drive unit to be easily adjusted with a simple turn of a set screw located on the outside of the unit. An optional dual stage pressure valve can also be added to change pressure settings during the course of a run. Low pressure settings at the starting line allow turbocharged and supercharged drivers to build boost, while a higher pressure setting is applied after launch to allow for converter “lockup” down track. This option is ideal because of the increased power being built in the latter part of the run. Bruno also states that by running a converter drive, you will reduce the transmission operating temperature by at least 100 degrees over conventional setups.

Operation with a Bruno converter drive system is typical of any transmission: the transbrake is used just as a clutch pedal would be, stopping the input shaft so you can select any forward or reverse gear. Shifts downtrack are executed manually, electronically, or even air-assisted, depending on your style of racing and the rules of your sanctioning body.

Brandon Booher TAD

A Quick Drive and B&J transmission combination in the 5.3-second, 270 mph supercharged Top Alcohol Dragster of Brandon Booher.

As a side note, Bruno’s Automotive offers a converter drive cast from magnesium that is 7.5 pounds lighter than a standard drive unit, weighing in at 42 pounds including the bellhousing.

Converter Drive System Operation – Quick Drive

The Quick Drive converter drive unit operates similar to the Bruno, allowing coupling of torque converter setups to B&J, Lenco or Liberty transmissions. Quick Drive, LLC is based out of Parker, Colorado. Originally started by Top Fuel racer, Mike Strasburg at B&J Transmissions, it is now run by Steve Graves and family. The modular design of the Quick Drive converter drive unit allows racers the ability to change transmission ratios and service the gear box separately without removing the Quick Drive converter drive unit, the torque converter bolts, or the bellhousing assemblies from the vehicle.

The Quick Drive also employs a CO2-operated, quick-releasing transbrake that utilizes a nine-disc brake clutch configuration for increased holding capabilities unaffected by fluid temperatures. High-level fine tuning adjustment control over converter charge pressure and flow can change the characteristics of the torque converter for more stable, consistent and predictable results.

Leo Tavarez Rotary Mazda

Even import racers are getting in on the benefits of converter drive setups. Leo Tavarez has paired a Liberty transmission and a Browell bellhousing with his Quick Drive.

An optional input shaft speed sensor allows for monitoring of torque converter changes and efficiency. An available “Safety Sprag” clutch option eliminates engine braking by returning to idle when the throttle closes to reduce stress on the engine and rotating assembly (for vehicles up to 1,600 horsepower).

Steve Graves, owner of Quick Drive, says the future is looking bright for his converter drive units. “More and more, different styles of race cars are utilizing them due to their quality of products, service, and ease of use.  The blown alcohol set up is currently the most popular combination running converter drives in drag racing, with great success.”

Converter drive units are frequently found in the Top Alcohol, Pro Mod, Top Sportsman, and Competition Eliminator categories, but racers are beginning to utilize the converter drive technology even down to the local bracket racing level for their consistency, dependability and ease of maintenance.

Quick Drive “Quick Lock”

Quick Lock New Install Russell Wullenwaber

The lock-up version of the Quick Drive, the Quick Lock, in Russell Wullenwaber’s diesel-powered Camaro.

Expanding on the capabilities of the converter drive, Quick Drive has also developed another innovative device aimed at evening the playing field between torque converters and clutches.    This technology focuses on the way power is applied at different areas of the track between torque converters and clutches. While torque converter-equipped drag racing vehicles typically are quicker in the early part of the race track, they’re at a disadvantage to their clutch-driven counterparts in the back end of the race track and in ultimate mile-per-hour capabilities.

Through racing torque converter technology advancements and design over the last decade, Quick Drive introduced their Quick Lock system to combine the advantages of their converter drive system on ease of maintenance with a torque converter, while addressing the lock-up capabilities of a clutch-driven system. Using the same basic principal of non-lock up torque converters (impeller, stator and turbine), a lock-up converter adds a mechanical component that “locks” the turbine to the housing, thereby locking the input shaft of the transmission directly to the flywheel on the engine. This provides the same or better efficiency as a conventional clutch at the later points on the track, while retaining the torque multiplication benefits of a non-lock up converter in the early stage of the run.


The Quick Drive Quick Lock system utilizes a hydraulic control activating a multiple disc clutch pack to lock the converter, while still maintaining the tuning capabilities in pressure and converter charge/flow rates. Unlike other lock-up systems, the Quick Lock’s unique pneumatic controlled spool valve controls pressure and flow rate for tuning control and adjustment of the lock-up clutch. Modulation of lock-up pressure and rate of flow can be controlled via time based or RPM based schedules from a variety of popular external products available on the market, and does not require a dedicated control unit.  This allows tuners to incorporate lock-up control rate and quick-release modulation to prevent loss of traction and engine bogging, and allow slippage during gear changes. Currently, lock-up style converters are not legal for many drag racing sanctioning bodies, but the technology is proven in truck and tractor pulling, monster truck performance, and many other arenas.


A side view of a Quick Drive mated to a two-speed Liberty transmission. While the pan appears radically deep, Quick Drive confirms the lowest point of the pan is 7.5-inches below the centerline of the crankshaft.

From The Engineers

The most successful combination thus far using a converter drive has been the blown alcohol setup. Steve from Quick Drive believes it’s how the supercharger is able to apply power down-track and the ability to adjust the drive to the ever-changing track conditions that gives this combination a nod in benefitting racers. With its ability to be adjusted to any track condition, run cooler and thus create less wear and tear on parts, and the greatly reduced need for maintenance, converter drive setups seem like a no-brainer for those with the resources and the need to chart that direction.

With anything, however, there are tradeoffs to take into account. And as Bruno Massel, Jr. shares, the principle points are the initial cost of entry, and the physical weight of adding the converter drive to the car.

“The only thing that we’ve ever encountered racers being concerned about is the weight. By the time you pair a converter drive with a Lenco transmission, it’s heavier than a Turbo 400 would be.” Bruno’s has been able to combat this by working to develop the aforementioned lighter-weight magnesium case and components, having shaved off seven pounds with their latest converter drive unit. In working with Liberty on their Extreme transmission, Bruno’s has been able to get the combination down to the weight of a Turbo 400, thereby eliminating this previous disadvantage, if you truly want to call it that.

Beyond that is the initial cost; while a steep price tag for some of your more mid-level drag racers, for those competing in Pro Modified, Top Alcohol Dragster/Funny Car, and similar categories who prefer the freedom of the manual transmission, that cost can be easily weighed against the continuing price of consumables involved in a clutch combination (discs, floaters, and associated tools).

Jay Payne's supercharged Pro Modified Camaro with a Bruno's BRT converter drive unit.

Jay Payne’s supercharged Pro Modified Camaro with a Bruno’s BRT converter drive unit. (Bruno’s Automotive photo)

“A big part of it is the initial investment. For Pro Modified racers, they’re spending an exorbitant amount of money already, and so that cost isn’t an issue. But a lot of racers in X275 and similar classes, when they’re stepping up in horsepower, it’s an incremental change and they can get a Turbo 400 or a Powerglide to hold, because they’re running on a smaller size tire and don’t want to hit the tires hard. So, they can get away with running a Glide or a 400 without making that investment in an $8,000-9,000 Lenco transmission and the cost of a converter drive. It’s a more significant investment for these racers.”

Operationally, Massel, Jr. says there are no parasitic losses over and above a pure automatic to take into consideration with a converter drive, and in fact, there are functional advantages to how the unit works.

…with a Lenco behind it, you can spin the output shaft with your two fingers — try doing that with a Turbo 400. – Bruno Massel, Jr.

“Our pump only has one function, to service the converter. As a result we’re able to run more converter charge pressure which makes the converter more efficient,” Massel, Jr. explains. “A regular automatic has 200-220 pounds of line pressure, but the converter only sees 50 to 60 pounds of that, which is the bleed off from what goes to the clutches. In our unit we can run as much as 250 pounds of converter pressure, because we don’t have a clutch pack or valve body to feed, so you will get better coupling and more efficient use of your converter.”

Illustrating this, Massel, Jr. shares that “with a Liberty behind it, you can spin the output shaft with your two fingers — try doing that with a Turbo 400.”

What The Racers Say

Many top-caliber teams are utilizing both the Bruno and Quick Drive style converter drives, and many championships have been won utilizing the technology. Racers like Jirka Kaplan in NHRA Top Alcohol Funny car, and Bruno Massel in NHRA Competition Eliminator have proven the performance of the converter drive system, and far more have utilized the technology in a wide variety of combinations and racing divisions and classes imaginable.

Clint and Jim Hairston, who won the Pro Modified class at last year’s Street Car Super Nationals’ race at Las Vegas Motor Speedway, have posted an elapsed time of 5.759 at 255.24 mph using the new converter drive unit from Quick Drive. They’re one of several turbocharged racers reaping the benefits. Bobby Cottrell, a west coast Heritage series racer, has switched from a traditional automatic to one with a converter drive. He stated that he’s able to be more consistent at any racetrack he runs his blown alcohol front engine dragster at, with virtually no maintenance between rounds.

Some other big names include Don Walsh Jr., Doug Winters, Mike Knowles, Mike Janis, Don Wooten, and Todd Tutterow, just to name a few, who have made the switch to converter drive combinations. More recently, Extreme Pro Mod racer John Stanley has switched to using a converter drive to maintain some consistency in his program. John has run every combination from clutch to full automatics and states that the converter drive is the only way to go. The common theme amongst all the customers utilizing the converter drive system is its ease of use. Maintenance, reliability, consistency have helped all these teams with nailing down their setups. Simply stated, they love it.

Article Sources

About the author

Eddie Maloney

A resident of Las Vegas, Eddie has been involved in drag racing most of his life. Currently an NHRA tech and photographer, he has served 17 years in the military.
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