So the J58 has the bypass capability but it will only bypass in the high mach. One can also see it has paid the price in complexity at the turbine end. Mind you this a design from the 60’s. So at high speeds this engine is very similar to drawings I have been doing. The turbine is bypassed at about mach 2.1 and above. Engine pretty much just converts in to a big ramjet. It sounds simple enough but it has some complex features to deal with pressure build up. The Aerospike has to move and so on. Regardless it is yet another example a compound system that worked great.