A tri-power intake manifold refers to an intake manifold with three carburetors. The design was first used by Pontiac and is most often found in specialty models of American cars from the 1950s and 1960s. Some auto companies sold tri-power systems with three two-barrel carburetors.
The intake manifold regulates the flow of air into the engine in order to maintain the correct proportion of oxygen needed for the chemical ignitions that fuel gas engines. The air mixes with gasoline in the carburetor before being delivered to the ignition system. In a tri-power system, the additional carburetors act as secondary systems, allowing more fuel-air mixture to reach the ignition system at peak throttle conditions.