It was once pointed out to me (by Kevin Cameron) that a vertical twin is,in effect,only a very narrow angle V twin, and a boxer twin(ala BMW)is nothing but a very wide angle V twin. Ducati-90 degree,Harley-45deg, Triumph- 0deg, BMW-180deg. Power production is a factor of bore and stroke,breathing,and cam timing,not really angle of the cylinders.
However,power delivery is affected by the offset firing order of the Harley engine, which has a 270 degree firing order(as does the America,Speedmaster,and Scrambler,along with some of the Japanese V twins,and the Dreer Norton). This means that you get two close together power strokes,then a relatively long time between two more close power strokes. This is a big boon in low traction situations, and is the official reason that Harley has dominated dirt track racing for so many years.(The AMA rule book is the real reason,but that is for another post)
I am a Harley owner,and it might interest some of you to know that the rear cylinder actually runs a few degrees hotter than the front!
It's my opinion that the only reason that Harley developed a belt drive for their big cruisers,back in the late 70s, is that the parent company,AMF, would not fund what would have necessitated a complete re-design of their power-plant to accommodate a shaft drive.They came up with so many reasons(excuses) that a belt was better than a shaft,that now that they can afford a shaft,they are not about to eat their words,and build one. Now, of course, if you have a big cruiser,and you don't have a belt,you're just not cool. For a big cruiser,or touring bike,a shaft is better in every way. For almost every thing else,a chain is the way to go. It will stand up to dirt,rocks,and mis-alignment(read:ham fisted owner abuse)much better than a belt.
For a pampered bike, a belt is a lot less maintenance than a chain.
:chug:
Cheers!
Bruce