It can take 100+ extra horsepower to drive a supercharger even on a mild 600-700hp street engine, so the entire rotating assembly is going to see additional stress from the cylinder pressures over an n/a motor. However, for the same displacement the n/a motor would have to spin at higher rpm, which requires more expensive valvetrain components.
Cranks see maximum stress near TDC. Because boosted motors run less timing, the cranks actually see a lot less stress vs. a N/A motor.
Let see, the boosted motor has forced a lot more air and fuel into the cylinders and that ignites and makes a lot more power than a N/A combination would so how can that posiibly make less stress? BTW, I have made motor with Roots super charger that made peak HP (496 C.I.street hemi on pump gas 927HP) at 7300 on pump gas and N/A motors on race gas that made peak 730 HP( 471 C.I. wedge) at 7300 RPM. Same RPM for peak HP, which one has the most stress on the rotating components in your mind? Insert whistling Emotioncon here with smiley face after it. On your deal with the turbo where it does not drive the turbo off of the crank and it does not gain boost directly proportionally to RPM, depending on the throttle and gear it is in, it will not have the same stress per RPM as a supercharge motor will with all other things being the same. HP makes stress, less is less.
