One of the most exciting things about a performance street/strip vehicle is its launching power. And with an automatic transmission, much of the take-off is determined by the stall rpm of the torque converter. In this section, engineers at TCI® answer a few commonly asked questions about torque converter stall. What are the differences between flash stall and brake stall?
Flash stall is the true stall of a torque converter. Brake stall, or “foot brake stall,” is the rpm that occurs when the engine overrides the brake system and the car begins to “push” forward. You simply hold the brake and slowly accelerate until the car bogs the engine down and then begins to move forward. Which one is the more effective measurement of the two?
Brake stall is NOT an accurate way to properly check the stall because there are too many variables that affect it. Some of these variables include the type of brake system (drum or disc) and brake adjustment. Therefore, when measuring the stall of your torque converter, the flash stall will always be the more effective option of the two.
Note: Using the flash stall to launch from idle is also the more efficient way to “leave the line”, as it doesn’t have any effect on the engine during take-off.How do you check the stall in your torque converter? What variables factor in, etc?
For the typical street/strip application, the easiest way to check torque converter stall, as TCI® rates it, is by “flash stall”. This can be measured by pressing the accelerator all the way to the floor (full throttle) when the vehicle is in high gear at the lowest speed before it downshifts, and watching the tachometer. The rpm to which it instantly “jumps” is a pretty accurate measurement of the stall rpm of the torque converter. This method works even better if you have a full manual shift transmission.
The second way to measure flash stall in a street/strip vehicle is to floor the throttle from a dead stop off of idle. Look at the tachometer and whatever the rpm jumps to when the car starts to move is the stall rpm. If the cam is too big for the converter or if the rear end gear is too low, it will dramatically affect the stall rpm by decreasing it. In other words, a car with a 3.73 gear will flash stall a converter at a higher rpm than an identical car with a 4.10 gear.
For more information about torque converters or any other drivetrain questions, please call our toll free TRANS HELP® line at 1-888-776-9824, or visit our website at www.tciauto.com