And don't forget, too, Malcolm, that despite the presence of the Exhaust Valves in the head, the 6-71 is still a 2 stroke engine and the liners (specifically the port shapes and heights) control the timing of the Intake Cycle and cylinder scavenging, in much the same way as a camshaft controls valve timing.
Over the many years of the GM/Detroit Diesel engines, a wide variety of liners were developed to give different operating parameters, just as many 4 stoke engines had a range of camshafts for differing applications. The 6-71 has been used in Trucks, Earthmoving Plant, Locomotives, Boats, Gensets, Waterpumps (and even Tanks!). Each application had a unique need for power, torque and rpm range. The port shape in the liner is modified to optimise engine output to application.
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