The heaviest parts of any engine are the cylinders and crank, since they are the main load bearing items and are usually made from steel. Because of this, a boxer configured engine can be very wide, but also very low, good for eliminating top-weight that robs vehicles of cornering potential. The reason that they are usually torquey engines is because they are normally set to operate as two seperate 2 cylinder engines sharing the same crank, that is, about every 180 degrees the engine is experiencing 2 simultaneous power strokes on a much more compact crank, which helps to reduce the amount of power needed to accelerate the engine mass, and allows more power to be used by the gear box. Of course every manufacturer has their differing opinions and methods, but the main draw of a boxer engine remains it's low CG, no matter how you slice it.

I've just finished a lot of e-mail, and I'm sure I've left some stuff out, so I'll be back tomorrow to see what else I can add.

 

So two cylinders are firing at the same time?

 

Ugh.... I wrote that in a sleep-deprived state... the cylinders fire sequentially, but since the crank is much smaller, more power is put to turning the flywheel and running gear without sacrificing internal strength. A 3-main engine is normally the most you'll see in a boxer 4 cylinder, and the crank is well supported. My original statement made no sense, as any semi-well designed engine is going to have 2 cylinders fired with just 180 degrees of crank rotation, and I can't seem to get back in the state of mind that I was in before I left for 2 weeks so I'm going to have to think about this some more so I don't confuse everybody along with myself...