Maximum boost for this range (theoretically possible to be obtained) is higher that the actual automotive engines (in absolute value) may use but probably from the practical point of view, a double or a triple torque at low engine speed may be gain. From another point of view, maybe the most important gain is the extension of the operation area under PO surge line. Comparison with STO, the speed range under PO (in SO) may be double and have almost the same dimension like the pure PO engine’s speed range. Therefore, it is possible to estimate a double engine’s range speed in the case of SPCO comparison with the pure PO at the same boost if different tuning between compressors/turbines and engine are done. A more detailed examination of this feature may open the door of new class of high performance engines. From the other point of view, an important advantage is the apparition of the natural crossing points between SO and PO. This fact is possible because in SO the two stage compressor characteristics are always over the single line compressor characteristics. For Garrett To-4-60 turbocharger (like is shown in Figure 9), 95% of the compressors’ speed range has common points inside of PO mode and a natural transition could be done. Only at maximum compressor’s speed (126000 rpm) the transition point is just a little bit inside the PO surge line but from technical point of view in extreme situation (like race application) this point is also available (for short time).