Choose the Right Torque Converter

If you’re a part of the car racing scene, you’re definitely no stranger to the tune-up process between each race. As the connection between your car’s engine and transmission, a good torque converter can really make a difference in your car’s performance. However, finding the perfect torque converter is no easy task—it can depend on multiple factors, like your car’s weight, rear-end gear ratio, tire size, engine size exhaust, camshaft duration, and other technical factors. It’s always best to consult a professional mechanic before replacing your car’s torque converter—however, this guide will help walk you through some common questions you might run into along the way.

Steps

What is a torque converter?

1. A torque converter connects your engine to the rest of your vehicle. Think of your vehicle like a horse attached to a cart—the horse represents your engine, while the cart represents the weight, or “load” of your vehicle. The torque converter is like the hitch that connects the horse to the cart, allowing it to move forward. In your own vehicle, a torque converter translates the rotating engine into an effective power source.

What is stall speed on a torque converter?

1. Stall speed is the total RPM your car reaches before stalling. Within your car, a torque converter acts like a clutch, automatically converting the engine power to your car’s transmission. As your engine creates more power, its total RPM increases—the stall speed is just the specific RPM when your engine stalls.
   • Stall speed also depends on your engine. If you reuse a torque converter with a different engine, the stall speed will also be different.
2. A torque converter’s parts can affect the stall speed. The diameter of the converter, the total number of blades, and the amount of space between each individual component all play a part in your converter’s total stall speed.
   • For instance, a torque converter with plenty of clearance between its inner components will have a higher stall speed than a converter without much clearance.

How do I choose a torque converter stall speed?

1. Pick a stall speed that’s 500 RPM higher than the start of your camshaft’s powerband. A camshaft is a long rod that helps open and close the valves in your car’s engine. As a part of your engine, camshafts operate within a certain RPM range. Add 500 RPM to the starting number of this range—this is the ideal stall speed for your torque converter.
   • For instance, if your camshaft operates between 1,600 and 5,200 RPM, a good torque converter stall speed would be 2,100 RPM.

What is a good street stall converter?

1. A 2,000- or 2,400-stall converter works well for cam durations under 248 degrees. Consult the “cam card” for your camshaft—this is an informational card made by the manufacturer, and describes your “cam duration,” or how far the engine valves are rotated. If your cam duration is under 248 degrees, experts recommend going for 2,000- or 2,400-stall converter.
   • If your cam duration goes up to 268 degrees, a 2,400-3,000-stall converter is better.

What size torque converter should I choose?

1. Get a larger torque converter for a faster brake response. With larger torque converters, like a {{safesubst:#invoke:convert|convert}} model, your car will quickly respond to your footbrake, even if the engine is at a high RPM. A smaller-sized converter, like an {{safesubst:#invoke:convert|convert}} model, won’t react to the brakes as quickly.

What other factors should I consider?

1. Choose a larger torque converter for heavier vehicles. If your car is on the heavier side, it will put more strain on your torque converter. Similarly, lighter cars are easier for your torque converter to handle. Heavier vehicles tend to push your converter’s stall speed to the limit, while lighter vehicles don’t create nearly as much strain.
   • Drop by a nearby truck stop or weighing station to see how heavy your car is. According to the U.S. Department of Energy, “light-duty” vehicles are less than {{safesubst:#invoke:convert|convert}}, while “medium-duty” vehicles are between {{safesubst:#invoke:convert|convert}}.
2. Factor in your car’s rear gear ratio. Heavier cars tend to have rear gears with a low gear value, like 2.73 or 3.08. Since you need extra force to move a heavy car, the torque converter will end up stalling at a higher RPM. On the other hand, a lighter car has a higher gear value, and won’t need to reach such a high RPM.
   • If you have a heavier car, you’d need a torque converter that can handle the increased RPM.
3. Inspect your tires. Typically, cars with wider tires are a lot sturdier and reliable. Wide tires help you maximize your RPM, as opposed to a car with both large and small tires.

Who makes the best torque converter?

1. BorgWarner, EXEDY, and Schaeffler are well-respected vendors. BorgWarner gears their products toward all-wheel-drive vehicles, while EXEDY expands its market to both CVTs and regular cars with automatic transmissions. Additionally, Schaeffler specializes in torque converters for hybrid vehicles.
   • Yutaka Giken and ZF Friedrichshafen are also well-respected manufacturers.

Warnings

• Shuddering, overheating, and vibrating are all signs of a damaged torque converter. Take your car to a repair professional right away if you notice any of these symptoms.

References

See also

• Clean an Automatic Transmission
• Change a Saab 900 Clutch
• Replace a Serpentine Belt
• Test a Fan Clutch
• Measure the Torque (Twisting Power) of Your Favourite Car
• Improve Automatic Transmission Performance and Reliability
• Fit a Clutch Plate
• Replace the Reverse Light Switch on a 1999 Ford Ranger Manual Transmission
• Replace Universal Joints
• Change Transmission Fluid in a Ford F‐150 Pickup Truck

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