Thankfully, though, we have a neat explanation of the B58M30 01 courtesy of Engineering Explained's new video, which also points out that the Supra's BMW engine has a closed-deck block like you ...

The design promotes efficient cooling but lacks the lateral stabilization of a closed-deck block, which can lead to instability at Honda-capable engine speeds.

The Mitsubishi 4B11 aluminum block utilizes either a semi closed- or open-deck configuration (depending on model) that's limited by its stock bore size and the horsepower level it can sustain ...

The introduction of the S55 in 2014 brought the turbo inline-six to BMW’s M cars, featuring a closed deck block and higher boost levels, pushing the boundaries even further.