The McLaren Add-On Pack is a modification for Grand Theft Auto 5 that introduces multiple McLaren models into the game for players to use. This pack could include a variety of McLaren models, such as the McLaren P1, 720S, 650S, and F1. The exact specifications of each car can vary, but generally, McLaren vehicles are known for their high-powered engines, impressive acceleration, and high top speeds.

For instance, the McLaren P1, known for its hybrid powertrain, can reach from 0-60 mph in just 2.8 seconds, as well as achieve a top speed of 217 mph. The 720S is also a show stealer with its 4.0 L M840T twin-turbocharged V8 engine, maximum output power of 710 horsepower, and impressive top speed of 212 mph. Each model is added with meticulous attention to detail and provides a highly immersive and realistic gameplay experience in the world of Grand Theft Auto 5.
 
Please note that the actual models included and their specifications can vary depending on the exact details of the mod pack.

Credits:
EliteSamOfficial, Zen-Imogen, EvertW & Maxim_aka_Pianist (Maxim Gorbanev)