Never add "X" amount quarts and let it rip. You could be underfilling or overfilling. BOTH are bad. An overfilled pan will rob power and put more strain on the motor. And underfilled will yield low pressure.
I'm sure you all know this, but the proper way to fill the oil is to add it until it reaches the correct level on your dip stick. Ford simply states for our vehicle it will be approximately 6qts. When the engine is cold, the oil should read halfway up the measuring area on the stick.
If you aren't measuring the oil level, you are doing it wrong.