Originally Posted by rdcyclist
The prime reason for the Boxer engine is perfect primary harmonic balance. For a given displacement, an inline configuration cannot approach the smoothness of the Boxer. This is why Porsche, Subaru and most light aircraft engines are Boxer Configuration. In the case of the light aircraft, there is the small matter of FAA certification and difficulty of obtaining said cert...
In a boxer twin, rocking couple is introduced because of the con rod offset.
BMW uses an inline six for their automotive products, which is far, far smoother than a boxer motor. I would say that an inline six is far smoother than a boxer.