I have some experience with Guzzi V twins. As I understand it, the main advantage of a V layout - especially 90 deg - is that you get perfect primary balance with a common crankpin (light & compact). When one piston is stopped dead, the other is at maximum velocity. This gives a smooth engine, despite the power strokes being uneven. Ducati is another maker to exploit this principle.
Flat motors are a different bowl of sauerkraut. They have perfect secondary balance because the power strokes are even, but the primary balance is bad. A Beemer twin has a totally different sound and feel from a Guzzi. I know which I'd rather throw a leg over.
Sorry to rain on your parade, but that's almost completely wrong. Flat twins have pretty well perfect primary balance because the pistons are moving in opposite directions at the same velocity and hence their accelerations (out of balance forces) exactly cancel out. Con-rod motions do not cancel exactly and give rise to secondary OOB forces which can be largely mitigated with crank balance weights.
Ninety degree vee twins can have very good primary balance, but not perfect. This is because the sinusoidal motion of the crank balance weights does/can not exactly match the linear motion of the pistons and the forces due to transverse motion of one con-rod interact with the linear vibrations of the other.
Even power pulses has no direct bearing as such on either primary or secondary balance forces, but does have an effect on the perceived smoothness of an engine I agree. Typically, one decides on the configuration based on balance and structural design criteria and then sets the firing order to get even firing pulses. Firing pulses can have a significant effect on overal engine vibration, particularly in setting up resonances, but this is not the same as primary or secondary balance issues. Those would be present even if the engine were driven round with the plugs out, which is indeed a now redundant means of assessing and measuring balance.
All the above also ignores rotational/torsional balance which is not insignificant and one reason why balance shafts if used invariably run in the reverse direction to the crank.
If you want a decent starting text on the subject try digging up a copy of An Introduction to the Mechanics of Machines by
Morrison & Crossland.
I do however agree that I'd much rather thrash a Guzzi round the lanes than try to keep a whip-iron Beemer beween the kerbs. MkII LeMans vs R90, a rather unfair contest perhaps, but it made an impression on me.
Richard
