[Westyfield2]

Does anyone know what the B48B20A vs B48B20B differences actually are?

Tuners report different power levels after mapping, so it can’t be software as they'd otherwise both remap to the same. e.g. BR Performance list the B48B20A as 340BHP and the B48B20B as 400BHP.

There's been some suggestions that it's stronger pistons, but if that were true they'd also both remap to the same... and just the stronger piston variant would simply be more reliable than the weaker piston variant when tuned the same.

Is it something else internal related like piston / cylinder head, but not just strength, which results in the engine having a different compression ratio and hence the power difference?

Or is the difference external in the turbo / exhaust / intercooler / etc?

[Knifeedge2k1]

The 20A has higher compression pistons is the main difference in rotating assembly

There's a bunch of other stuff that's different in the head and supporting equipment but the easiest way for you to check is to look at bimmercat.com

[Knifeedge2k1]

20i with B48B20A
https://bimmercat.com/bmw/en/search/...20i+B48/ECE/11

20i with B48B20B
https://bimmercat.com/bmw/en/search/...0i+B48D/ECE/11

30i with B48B20B
https://bimmercat.com/bmw/en/search/...0i+B48D/ECE/11

You'll see parts in the the B48B20B in the 20i and 30i are basically identical but the parts from the B48B20A are different part numbers (doesn't mean they're shittier or whatever, just different)