Twins vs V-Twin Engines


The most recognizable motorcycle engine in the world is the V-Twin. Whether it's chugging along for cruising the Thai country side in a Harley-Davidson or screaming its way to yet another world superbike championship inside a Ducati there's no doubt the V-Twin engine layout is successful. But why is it that? And more to the point, what does layout mean anyway?

It's not uncommon for men to fantasize about riding V-Twins. I'm told it's the same for women too, which only goes to prove how universally popular this particular engine configuration really is. And it is popular. In terms of how long it's been powering motorcycles, the V-Twin is second only to the single-cylinder layout, which had to come first for obvious reasons. So what is it about the V-Twin engine arrangement that makes it so enduringly popular, and are all the stories about exceptional grunt really true?

Before we go too far we should point out that there's more than one way to twin an engine – the most obvious being to stick two single cylinder engines side by side to create what's called a parallel twin. If we fail to line the two cylinders up of course, we'll get a V-Twin.

The term V-Twin actually covers a number of designs as the V doesn't relate to a specific angle. In the past manufacturers have used V-angles ranging from 42° - 70° while the rest seem to have settled in the region of around 60° to 65°. Then of course there's Ducati and Moto Guzzi who favor the 90° twin, which can be referred to as an L-twin or, more commonly, a 90° V-Twin.
Above 90° there's nothing until we get to what could be described as a 180° twin – or Boxer as it's known by BMW riders. This opposed twin is the logical extreme in the transition from parallel twin to V-Twin and is almost a marketing too by itself. However, there's a lot of misunderstanding about the V-Twin layout and what it can and can't do for your riding, so let's look a bit closer at what makes them tick.

Imagine a 500cc parallel twin. Now, imagine an identical engine but with a V-configuration. Which one has more torque? The answer is neither. It's common for people to talk about a V-twins torque, but the angle of the cylinders themselves has nothing to do with this – which is why one manufacturer can make a parallel twin go head to head with a V-Twin.

Why then, do we all have this 'thing' about V-Twin? It's probably to do with the number of cylinders, rather than the way they're laid out. With a single-cylinder the limitation of the single cylinder engine is its ability to rev and make power. A twin addresses this by adding flexibility to the design. Rather than having a single cylinder of say, 600cc with four valves, we can now have two cylinders of 300cc with four valves each.

The engine is the same overall capacity, but much more efficient in terms of filling and emptying each combustion chamber. Also, because either the bore can be smaller or the stroke shorter, it can be revved faster before the limit of the components is reached. As an added bonus the extra valve area lends itself to more revs too, so it can fuel and make torque at those extra revs.

However, while our imaginary two cylinder 600cc engine will make more power than our single cylinder 600cc engine, it will make roughly the same torque. So in this instance the twin has less mid-range. Compared to a four cylinder engine though, but that is another story, it makes its peak power and torque with fewer revs than an inline four – giving the impression of having more mid-range.
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