The BMW 3- and 4-Series are effectively the same car, only the 3-Series comes with four doors while the 4-Series uses two (replacing the outgoing 3-Series coupe). When it comes to the 2015 M3 and M4, same rules apply. They both shed weight compared to their predecessors, go faster, produce better fuel ratings, and ditch their V-8 motors in favor of a brand new twin-turbocharged inline 6.
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