According to engine’s speed, crossing maneuver must be achieved somewhere between 3000 rpm and 4500 rpm. In any case crossing maneuver must be done inside the common area of inline compressor map & PO map, as shown in Figure 2. Figure 3 shows in detail the transition area when two turbochargers Garrett T3-40 are used. Figure 3 shows extremely clear that between inline compressor characteristics and PO characteristics there are not any crossing points. More, all characteristics of inline compressor are situated under the PO characteristics and the pressure differences between same compressors’ speed characteristics are increasing with the pressure ratio. Let’s consider an example in Figure 3 where points D and E are chosen. Point D belongs to inline compressor characteristic at 153400 rpm and to PO mode characteristic at 132900 rpm. For Garrett T3-40 Compressor’s, point D is also in the neighborhood of PO surge line. This mean that if the engine requires 140 kPa of boost, for the interval time of crossing maneuver the inline compressor must decelerate very fast with approximation 20000 rpm. For point E where only 70 kPa are required, the inline compressor drop speed could be only 2000 rpm. The same general idea could be seen at the majority of turbochargers actually on the market. In this global Downloaded from SAE International by Nan Kai University of Technology, Monday, December 02, 2019context, we may emphasize the next six general issues regarding crossing maneuver between inline compressor and PO mode in STO’s case: