B46 changed a few things that didn't affect power output to give it lower emissions which brings to it SULEV status in the US. MPG got tweaked by ~1 MPG compared to the 2014 B48 Cooper S engine.
For anyone wondering about the different engine types here's a post I did last year on another forum:
There are quite a few engines MINI has used over the years. The "R" lettering refers to specific MINI models, which may have different engines used within that model. For example, the R56 came in Cooper, Cooper S, and JCW trims and used 6 different engines between the trims throughout it's life.
Here's all the engines I can remember sorted by model. I generalized a lot to keep it simple, which engines came out when and to what is...complicated, but this will give you a good idea where the different models and their engines line up :
1st Generation (Tritec Engines):
R50 Hardtop/R52 Convertible/R53 Cooper S Hardtop: W10 (Cooper) / W11 (Cooper S)
2nd Generation (Peugeot Engines):
R56 Hardtop (all trims)/R57 Convertible: N12 (Cooper) / N14 (Cooper S/*JCW)
2nd Generation LCI (Peugeot Engines):
R56 Hardtop/R55 Clubman/R57 Convertible/R58 Coupe/R59 Roadster/R60 Countryman/R61 Paceman: N16 (Cooper) / N18 (Cooper S/*JCW)
*JCW engines were technically the same engine with some slight modifications (different pistons, bigger turbo, different tuning)
3rd Generation (BMW Engines):
F56 Hardtop/F55 4-Door Hardtop/F54 Clubman/F57 Convertible/F60 Countryman: B36/B38 (Cooper) / B46/B48 (Cooper S) / B48M (JCW)