A thermal reactor is used in place of the conventional exhaust manifold on 1979–80 RX-7 models. It is used to oxidize unburned hydrocarbons and carbon monoxide before they can be released into the atmosphere.
If the engine speed exceeds 4,000 rpm, or if the car is decelerating, the air control valve diverts air into passages in the thermal reactor housing in order to cool the reactor. (On later models equipped with catalytic converters, air flow into the reaction chamber is cut off under these conditions.)
A one-way valve prevents hot exhaust gases from flowing back into the air injection system. The valve is located at the reactor air intake.