Each J-58 engine has six, large diameter bypass tubes running along the sides of the engine. At high Mach, a portion of the entering air is bypassed around the compressor and turbine sections through these tubes, giving the engine stall free operation. This bypass feature led to the description of the J-58 as being a turbo-ramjet engine.

Located on the top and bottom of the engine inlet were the forward bypass doors, used to relieve excess air pressure inside the inlet. At supersonic speeds, the louvered doors were controlled by the Air Inlet Computer and modulated from open to closed to relieve excess pressure building up in front of the compressor. The forward inlet doors worked together with the inlet spike to achieve optimum performance efficiency.

Another component of each inlet system are a second set of doors, called the aft bypass doors. Positioning the aft bypass doors was a manual operation by the pilot. The aft and forward bypass doors worked in opposite directions to each other. If you opened the aft bypass doors, the forward doors tightened down and vice versa. The purpose of the aft doors was to help manually keep the forward bypass doors from being too far open. When all of the inlet system components were working together properly, the system would utilize the supersonic airflow to produce massive thrust.