Dynamometer Readings With High Stall Converters

There is a misconception and a lot of misinformation about the poor vehicle performance numbers that are generated by testing a car with a high stall torque converter on a dynamometer. Most people that are not familiar with how a torque converter operates will automatically think that the torque converter is inefficient. This is totally false and the following facts are why you should not believe the dynamometer numbers while using an unlocked high stall torque converter. All late model dynamometers have a software program that commands the loading and speed of the vehicle over a certain period of time while making a test pull. The software used in these dynamometers is setup to be used with a locked 1:1 connection between the engine and the rear wheels, such as using a standard shift transmission in 3rd gear or when an automatic transmission has the torque converter clutch locked. When an unlocked high stall torque converter is used to make the pull and the dynamometer software has not been changed to allow for the fluid coupling differences the dynamometer readings will all be bogus. For instance, the low rpm torque readings will be high due to the torque multiplication of the torque converter being run in partial stall. Likewise, the high rpm torque readings will be low due to the long period of time the dynamometer takes to allow the torque converter to transition from partial torque multiplication to a hydraulic locked condition. The only cure for this phenomenon is to rewrite the dynamometer software to prevent this from happening. Torque converters with a low STR or low stall are not as adversely affected by this phenomenon. The high rpm transition problems never occur when the vehicle is being driven or raced normally. Therefore, worrying about what the dynamometer numbers are is a total waste of time.

Things to consider when putting an auto with a high stall on the dyno.

(1.) lock the torque converter clutch and do the testing,

(2.) use the readings you get with an unlocked torque converter as a baseline and continue to tune the car like normal until you get the best numbers remembering these are just numbers and not the actual horsepower and torque or

(3.) use a dynamometer shop that gives you the service you deserve for your hard earned money.

The only really true test of the performance of a vehicle is to take it to the track and see what ET and MPH the car will run.