Of course it only uses heat energy that would be lost out the exhaust, but there are fluid flow losses on both sides (gasses or any other fluids flowing through pipes consume energy just to keep them moving; the flow losses in a turbo system have very little to do with the oiling system for the centerbearing(s)), and the energy consumed by the compressor side is big fluid flow energy consumer. The the turbocharger does enjoy an adiabatic efficiency advantage at equal volumes and pressures that can exceed 15% because the compressor turbines are generally more efficient than the methods used by superchargers and hence they heat up the incoming charge less, but turberchargers are often run at higher boost pressures and hence require an intercooler, a further fluid flow loss, but one that is offset by the denser incoming air harge it creates. My point is simply that the energy required to raise a given volume of air a specified psi over ambient doesn't change much regardless of how you do it. The only thing that changes is where the energy comes from and the sources of the losses introduced. And if a street exhaust system is making significantly more backpressure than a turbocharged system, either there is something wrong with the street system or the method of pressure measurement needs to be seriously re-examined in both systems.
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