When it comes time to get engine power to the ground, if running an automatic transmission, it has to pass through the torque converter. Selecting one of these hydraulic couplers can be a daunting task if your hot rod has more power than when it came from the factory. While many have a firm grasp on the technical aspects of a converter’s function, and how to select a good stall speed, some are still not comfortable making that decision.
In October 2017, we teamed up with ATI Performance to assemble an article that clears the air about the subject. The article was titled, Stall Speed Basics: What Goes Into Stall Speed In A Torque Converter, and with the help of Dave Caine of ATI Performance, we explained more about what goes into making the proper selection. For that reason, I thought we would focus this week’s Throwback Thursday on this great article.
In a nutshell, A torque converter’s function is to take the engine’s mechanical force and convert it into hydraulic pressure. Its impeller turns at engine speed, and the more torque the engine makes, the higher in the RPM range the converter will “stall,” or lock up. The stall speed is the level at which the engine’s force can’t overcome the hydraulic pressure and varies for a number of reasons. The action of the converter’s stall is what helps the car accelerate at a peak level once the driver applies the power to the driveline.
In the original article, Dave offers some great insight. “The overall size of the torque converter has to do with its efficiency and holding power,” he says. “In general, the larger the converter, typically, the tighter and more efficient it will be. The more torque your engine makes, the more holding capacity you need from your torque converter. You also have to be aware of that capacity because you can’t have too much, or it will hinder performance at the track. If you have too little holding capacity, you will start to blow through your converter and experience slippage. The RPM range of the torque and horsepower curves are most important in configuring a converter correctly for a given engine combination.”
Before you start making phone calls to order the correct convertor, you’ll first need to figure out the primary purpose of the car. If you’re looking for something that’s going to be used at the track only, the process of selecting a converter is simpler for the manufacturer. However, when you start creeping into the realm of street/strip use or daily driving, that’s where things get tricky. Knowing the combination and its use is the best way for a torque converter company to build a converter to fit your needs.
There is a lot more vital information in the original article, and that is why I selected, Stall Speed Basics: What Goes Into Stall Speed In A Torque Converter as this week’s Throwback Thursday showcase article.