A boxer engine is a flat, horizontally-opposed engine (think of it as a 180 degree vee engine). The “boxer” monicker comes from the pistons in each bank acting like the fists of 2 boxers facing each other.
Subarus have either a flat 4 or a flat 6.
Advantages of the boxer configuration is natural internal balance (because of the 180 degree configuration) and a low center of mass. However, they tend to be much noisier than the same displacement engine in a straight, or traditional vee configuration.
Ferrari had a 12 cyl boxer in the 1970’s (Ferrari 512 BB) and Alfa Romeo had a flat 4 in the same period in their Alfasud series.
“Ferrari had a 12 cyl boxer in the 1970’s (Ferrari 512 BB) and Alfa Romeo had a flat 4 in the same period in their Alfasud series.”
Ferrari’s 12-cylinder boxer is, strictly speaking, not a boxer; the crankshaft in their engine looks basically like one from an inline-6 or V12 engine, and Ferrari themselves referred to it as a “180-degree V12”. Using a traditional boxer crank (with the rod journals set 180 degrees out from each other) would have made the engine a LOT longer, and with six cylinders on each bank the engine is pretty smooth anyway.
This engine, shrunk to a displacement of 3.0L, also formed the basis of Ferrari’s F1 engines for much of the 1970s.