While visiting an independent Porsche shop, I was told that in the case of a turbo engine, something like a bypass pipe could end up decreasing power delivery because it reduces back pressure too much. Could someone with technical expertise explain this please? Is this because too low of a back pressure is detrimental to the turbine's ability to compress air? What parameter is affected, horsepower, torque, or both?

From one end of the spectrum--very low back pressure of bypass pipe, to the other--high back pressure of stock, I imagine there is a middle ground of Tubi/AWE/Cargraphic exhausts, with mid level back pressure? Is it possible for this middle ground to be worse than stock?

Thanks in advance.