Power or powerful. Horsepower or hp. Torque or “torquey.” These are all words in the common vernacular of engines, more specifically motorcycle engines. Some will attempt to sidestep the issue with lofty denials of having no concern with this aspect of motorcycling. Instead, they choose to engage at length in discussions of scenery or freedom, among others. The truth is that every single one of us, motorcycle enthusiasts, has a fetish for power. It’s really that simple.
So, what is power more generally, or horsepower and torque more specifically? We all know, for lack of a better description, that mysterious force that propels us and our motorcycles down the road or trail. But how does it work? Read on and find out.
All About Work and Energy: Understanding the Motorcycle Engine
Regardless of their configuration or number of cylinders, all engines are designed for one single and unique purpose: to perform work. Anyone who has performed any type of physical work knows that it requires energy. In the case of an engine, then, do we “create” this energy? Well, it turns out that energy cannot be created. In fact, Principle of Conservation of Energy states that energy canNOT be created, it can also NOT be destroyed. It can only be transformed from one form to another. It follows, then, that the energy required to perform work must be transformed from another source.
Going back to our familiar example (ourselves), our bodies use the (chemical) energy contained in the food we eat and air we breathe and transform it into the mechanical and kinetic energy (as well as thermal, of course) that enable us to get work done. Unsurprisingly, the engines in our vehicles also transform energy. More specifically, an engine is a tool that allows us to liberate the stored chemical energy contained in the fuel (and air) and transform it into another form of energy that is more useful to us.
It is rather ironic to think that many of us ride our motorcycles to forget about the worries of everyday life, especially work, when at the same time our rides are made possible by work, more specifically that performed by the engines in our motorcycles.
Force and torque: Essentials for Engine Performance
The Oxford English Dictionary defines force as “An influence tending to change the motion of a body or produce motion or stress in a stationary body.” In the case of an engine, the expansion of gases following the ignition of fuel in the combustion chamber exerts a linear force as it attempts to push the piston down the cylinder. This force, in turn, attempts to cause the crankshaft to rotate, thus transforming the linear force into a much more desirable and useful rotary force. More concretely, this interaction produces torque, a torsion force. The magnitude of the torque depends on two factors: the force applied and the length of the lever on which said force is applied. Note that the angle between the two is also a factor, but for the purposes of this article, we will treat it as a constant. So, in light of the two aforementioned factors, it is hardly surprising that the unit of measure for torque consists of an element for force and another for length (i.e.: lb-ft or N·m). Unsurprisingly, the larger the torque reading, the greater is the twisting force being applied.
Power of Motorcycle Engines: Beyond Horsepower
Power is the measure of the ability to do work. As we all know, getting (physical) work done inevitably involves motion. For example, imagine someone trying to move a refrigerator. One may push, or exert a force, to the utmost of his ability, but until such time as the refrigerator actually moves, no actual work has been accomplished. Getting back to our earlier engine example, regardless of the torque being exerted by the crankshaft, no work can be carried out until the crankshaft actually turns. This also leads us into the final piece of the power puzzle, the element of time. So, to wrap up, while torque is an absolute measure of the force generated by an engine, power is the measure of its ability to perform work in a given time frame.
To help visualize the concept, think of a task (work), such as displacing a pile of sand. Now, imagine if you will, if the volume our sand pile is 100 m3 and that the task must be completed in 100 seconds. For the sake of simplicity, let’s disregard the distance involved. In such a case, we could displace 1 m3 of sand per second for 100 seconds to get it done. Alternatively, we could also accomplish the feat by opting for a larger shovel (increasing the force) and slowing down the rate (reducing speed). Of course, we could also use a smaller shovel and increase the rate of dumping, or any number of combinations of shovel size and speed to accomplish the mandate.
Engine Torque and Power
As the previous example illustrates, an engine’s power (again, its ability to perform work) may be increased either by increasing its torque output or raising its speed. Similarly, it follows that, at equal torque, an engine spinning more (rpm) will produce more power. Conversely, at equal engine speed, an engine producing greater torque will be more powerful.
Behold, two long-time contenders in the Open-class Streetfighter category, KTM’s mighty 1290 Super Duke R (left) and Aprilia’s potent Tuono V4 1100 (right). Both produce approximately 160 hp at the rear wheel, but the KTM arrives at that figure via modest engine speed and the impressive torque produced by its 1,301 cc V-twin engine. The Tuono, on the other hand, compensates the lower (but still heady) torque delivered by its 1,078 cc V4 engine with increased rpm to match its Austrian rival’s power output.
