Choosing the right torque converter...

[BigWheelinBubba]

Choosing The Right Torque Converter


"If your car or truck has been modified to enhance performance, you probably need a [torque] converter with a higher stall speed," says B&M Racing & Performance Products (Dept. ETD, 9142 Independence Ave., Chatsworth, CA 91311, 818-882-6422, www.bmracing.com). "Most stock converters have a stall speed in the 1500 to 1800 rpm range.

"When you make performance modifications, you generally shift the engine's torque curve upward into a higher rpm range. Therefore, you need a converter with a higher stall speed so that you can launch the car in the fat part of the powerband.

"If the stall speed isn't high enough, the car won't be making power when you launch and you'll bog off the line. If your setup is really mismatched, the motor may even want to stall whenever you attempt to shift into gear at idle.

"So, a higher-stall converter will improve acceleration by allowing the car to launch at an rpm where it is making power."

How high a stall speed is too high? B&M says, "Obviously, you don't want to launch the car at an rpm that is past your peak power output. There's no point in bypassing the engine's powerband.

"You also have to consider the car's weight, braking system, engine displacement and engine combination when deciding which torque converter to use. Some converters are designed for high-revving lightweight cars. Some are designed for heavy cars that make a lot of bottom-end torque. And there are converters designed for virtually everything in between.

"The key is to match the converter to the motor and to the entire vehicle in question. This is where technical support staff can help. They'll ask you the right questions about your combination, including where your car makes power and how much it weighs, in order to help you find the right converter for your overall combination.

"A quick warning: You definitely don't want to get a higher stall speed than you need. That's because the higher stall speed creates more slippage, which generates more heat, which is hard on the converter and the transmission. If you are going to run a converter with a higher-than-stock stall speed, you'll want to install a transmission cooler to extend the lifetime of your components. (Amazingly enough, 85 percent of transmission failures are due to excessive heat.)

"Higher-stall-speed converters also generally are not available with a lockup clutch. Again, this means more slippage, more heat and less fuel economy. But the tradeoff may be more than worthwhile for high-torque applications, since a higher stall speed can substantially improve a vehicle's responsiveness."