All converters have a certain stall speed. Aftermarket high stall converters will obviously have a higher stall speed that a stock converter. Some people check stall speed by the foot brake method. This isn't the correct procedure to check the true stall of a converter, but it will give you the idea of what stall speed is. In order to do this, press and hold your brake pedal and gas pedal at the same time. Look at your tach and see what the maximum rpm is that you can attain before the tires begin to spin. For safety's sake, you may also want to set your parking brake. This will be your footbrake stall speed. If your car happens to have a transbrake, then you can test the true stall of the converter.