FYI: A low-temp thermostat improves performance in two ways: first by increasing the mass flow rate of intake air, and second by reducing the engine's tendency to detonate.
From the laws of physics, cooler air is denser than warmer air. Since horsepower increases as the amount of air and fuel burned increases, cooler air (with more air molecules per cubic inch) makes more power. The low temp thermostat allows the engine to cool down to a lower temperature than the factory thermostat to make more power. At the drag races, water can be sprayed on the radiator between races to drop the temperature and improve performance. A low temp thermostat ensures that you leave the line at the same temperature on each run to give consistent maximum performance for bracket racing.
A lower temp T-stat reduces the temperature of both the incoming air / fuel mixture and the surfaces of the combustion chamber, greatly reducing the tendency to detonate. Detonation is an audible pinging / knocking sounds, refers to the spontaneous explosion of the unburned air / fuel mixture in the combustion chamber. Detonation reduces power, and can severely damage an engine. A lower temp T-stat allows the engine to safely develop more horsepower.