Throwback Thursday: Choosing The Correct Torque Converter

Wow, how time flies. Not only is it once again time for another Throwback Thursday, but let’s do everything we can to make this a great day. The arrival of the day after Hump day means another week is almost over. For this week’s look back, I thought we would check out an article published in February of 2016. Yes, I’m going back a few years, but the information is still relevant.

When we first published, Torque Converter Basics: Do You Know How To Choose Correctly, we reached out to a few industry professionals at ATI Performance Products and TCI Auto. Both of these transmission specialists have been building torque converters for a long time, so getting the correct information from them was simple.

One of the first things we discussed was stall speed. There are many factors that determine at what RPM the converter will flash stall after it is installed in your car. When discussing converters that are race car specific, they are not built with such a wide range of stall speeds. According to Dallas Moss of TCI Automotive, “In most cases, manufacturers will rate the stall of a converter at flash-stall, which is slightly different than footbrake stall.

torque converter

When using an automatic transmission, it’s the torque converter’s job to transmit and multiply the engine torque and deliver it to the transmission. If you cut open a torque converter, inside you will find the turbine, stator with sprag, and impeller pump. The converter’s turbine is attached to the drivetrain via the input shaft of the transmission. When the turbine moves, the car moves.

In essence, a torque converter will never be able to footbrake stall up to where it is actually flash stalling. It’s very difficult to tell customers what they can look for as a footbrake stall, simply because of the variables that can cause it to either hit the mark or way undershoot it.” Moss continued, “There are basic factors and variables that can dramatically sway the amount of footbrake stall someone can see from a converter.”

Beattie told us, “The only true way to determine a converter’s stall speed is at the racetrack with the car in low gear when you launch. But another safe way to get a reading that will be within 100 to 200 rpm, is to have a manually shifted automatic transmission or a way to hold it in high gear (1:1 ratio). With your car rolling at 10 to 15 mph, mash the throttle pedal to the floor, look at the tachometer, and then lift your foot from the throttle. Some cars will spin the tires, but you should have a moment just before tire spin, to see where the converter spins the tachometer. Testing a two-step with the car on jack stands, in the pits, or anywhere you don’t let go of the button or footbrake and accelerate, is very hard on the internal parts of the converter.”

torque converter

To an extent, the overall diameter and the internal construction of a converter can cause a substantial change in footbrake stall. Typically, an 8-inch converter (depending on internal fin angle and the style of stator), will most likely flash stall at a much higher RPM than the 10-inch unit.

In the original article, we asked Beattie, about the single biggest mistake users make when selecting a torque converter. “Thinking one-size converter fits all and buying something that says it is a ‘X,000’ stall converter, just because it is advertised that way.” While that sounds logical, we wanted to know how to avoid making that mistake. Beattie continued, “Just knowing a few basic facts can go a long way, and always call the manufacture and ask questions. At a minimum, if talking about a street-driven car that has some power, is on the heavy side, and has a decent gear for cruising, you should know the rearend gear ratio, tire size, engine size, and what transmission is in the car.”

There is a lot more interesting and what might seem surprising information in the original article, and to learn more, you really need to check out Torque Converter Basics: Do You Know How To Choose Correctly?. Check back with us often, as we’ll be sure to bring you more great tech you can use.

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About the author

Randy Bolig

Randy Bolig has been working on cars and has been involved in the hobby ever since he bought his first car when he was only 14 years old. His passion for performance got him noticed by many locals, and he began helping them modify their vehicles.
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