[Toutouxc]

That isn't some turbo specialty, the effect is the same in both NA and turbo engines. And AFAIK it isn't really feasible anymore. I don't know about other manufacturers, but for example Volkswagen Group's EA211 EVO2 engines run pinned at lambda 1 no matter what.

[salawat]

All I know is my last turbo'd vehicle was always running at 13.8, and that was a 2013 Nissan with a turbo'd L4, and it annoyed the piss out of me. Pretty much guaranteed only getting 26 MPG at highway speeds. This was despite claims in the manual saying the AFR was fuel octane dependent & would automatically vary (which I found out through experimentation was full of shit). It just stayed pinned to 13.8 whether you ran 87 or 91.