"High Performance" VIN ID

What does HIGH PERFORMANCE mean for the 5th VIN letter of "N" or "P" in the 2 different VIN tags? What is the difference in the motors?

1976 Dodge Charger VIN Decoder:
N - 400 1 - 4BBL 8 cylinder "B" engine
P - 400 1 - 4BBL 8 cylinder "B" engine (high performance)