In general.......a single of any given size provides maximum torque at lower engine speeds.
Adding more cylinders allows higher rpm by reducing the size and weight of the moving parts. The smaller bores and shorter strokes make less overall torque - but since HP is torque x rpm the multi cylinder engines lose some low end torque....but can make up for it at higher rpm and provide more overall speed.
V-Twins or Parallel twins can be designed and tuned similarly. In general the Cruiser V-Twins made by Harley/Yamaha/Honda are low performance long stroke motors that make low down torque that makes them easy to ride - while Ducati and KTM focus on performance and have shorter strokes and bigger bores to allow higher rpm. Parallel twins can be low performance motors like used in the Honda Rebel or Suzuki GS400.....or more highly tuned to make HP.
The 4 and 6 cylinder bikes can usually provide a lot of low end torque by virtue of big engine sizes - while also providing big HP numbers as well. The engines can be tuned for maximum touring comfort and smoothness (BMW K bikes, Goldwing, Yamaha FJR) - or killer HP (BMW S100R, Hayabusa, GSXR, etc.).
The Suzuki Savage makes around 30 HP in the 650cc single - and so does the Ninja EX250 twin. The bikes are both really fun to ride....the big single makes a lot of torque and accelerates well up to about 60mph and can go 80mph if it has to......the little Ninja is smooth and rides great at lower rpm - but once you get up over 8,000 rpm the engine comes alive up to the 14,000 rpm redline......cruising at 75mph at 9,000 rpm is no problem at all and you can do it all day long. When you come out of a steep uphill curve on the Savage you just roll on the throttle - the little Ninja will want you to shift down 2-3 gears if you want to keep up with the group.
philthymike wrote on 07/09/19 at 17:20:53:Now I've been told that small displacement v-twins simply don't have the torque of similar sized thumpers. I believe it was also said that any twin under 1000cc wasn't worth having for this reason.
Yet my Ducati at 821CCs beats the snot out of every big twin cruiser that's gunned for it with absolute ease.
Bit of a conflict here. Am I being told wives tales, superstition and folk lore?
I think it boils down to what the engine is tuned for and who the target market is.....more than how many cylinders or in what position the cylinders are located (V-Twin, Parallel Twin, Boxer Twin).