Emissions standards are really the only difference between the B46 and B48. For the consumer there are no important changes between the two engines. The B46 is a Super Ultra Low Emissions spec (SULEV) engine, and is the primary engine available in the US. BMW only used this engine on 2020+ 540i, 740i, 840i, X5, X6, and X7 "40i" models as well as the 2019-2020 Toyota Supra. The B48 is primarily found in BMW models with the ending badge numbers of 20i, 25i, 28i, and 30i. A higher output version of the B48 is in some 2019+ 35i models. It's also in some Mini models along with the Toyota Supra.