OK, we’ll admit it: the heading is a little misleading.
Why? Because the importance of either depends on the nature of your needs and, of course, you ever can’t have one without the other, anyway.
If you want to shred your car tyres, you need some low-down torque, but if it’s land-speed records you’re after, then horsepower will always win out. So, what is horsepower and why is it so important? The same can also be asked about engine torque.
Truthfully, there is no definitive answer as to which is more important, so perhaps a better heading would be about understanding the balance between the two, how they interact or even how to influence an engine into giving more of one or the other.
What is power?
In this example, we’re sticking to just two definitions; Horsepower and Torque.
Either can be measured in a number of different ways – Brake Horse Power, Power Standard, Newton Metre, Watts, Pound / Feet and so on, our preference is for BHP (for Brake Horse Power) and Lb/Ft (for Torque conversion).
Both torque and horsepower can be felt when accelerating.
In very simple terms, torque is the force you feel pushing you back in your seat on acceleration, horsepower is the speed achieved at the end of that acceleration.
In fact, brake horsepower is derived from a calculation that relies on torque: BHP = Torque X RPM / 5252. So what is torque, when defined simply? In essence, it is the ability to turn something, in this case, a flywheel.
Not all engines are the same, as even two units pulled from the same line will differ on an engine dynamometer. Even then, it would need to be a fully-controlled environment as the air pressure, temperature and humidity will all affect the power readings of an engine, even more so when we bring forced induction into the equation.
Furthermore, it’s possible to shape the characteristics of power: for example, a long stroke engine will generally give more torque than a short stroke. On this same basis, we can play with the cam timing to affect the power delivery – advancing the cam timing should deliver more low-down torque, while retarding it equates to high RPM horsepower.
Most modern engines strive for a balance of torque vs horsepower.
Another element to consider is forced induction (FI). Supercharging or turbocharging the engine is a great way to increase ‘power’, usually in quite a cost-effective way. Here, again, we have two routes, both offering different options. Supercharging, on one hand, will generally give you more torque, whereas a turbo will give you extra horsepower
Of course, we need to add a caveat. Either method increases ‘power’, but there are a lot of other factors you’d need to consider. For the sake of simplicity, however, that’s what you could expect to see by taking the FI route.
One further consideration when it comes to engine design or type, you should also consider the choice of fuel. This relationship with fuel type is becoming increasingly blurred. At one time, diesel was considered truck fuel and petrol was for motor cars.
Today, that is no longer the case, as diesel cars account for approximately 47% of new car sales, the figure having a experienced a minor slump after the infamous Volkswagen emissions scandal. Not only are they competing head-to-head for new car sales, but they are also making an enormous impact on the race track; as manufacturers such as Audi and Peugeot only enter diesel cars in the famous 24-hour Le Mans motorsport race for example – the torque and fuel economy are ideally suited for endurance racing.
When it comes to torque vs horsepower, it really is a question of application; if you’re trying to pull a tree-stump out of the ground, horsepower isn’t going to do it (unless you were to add a 100 metre length of rope and give yourself a run up). Yet, if it’s something a little more sporty, horsepower has to be the way forward. Most manufacturers have found their own ideal blend but, as we’ve seen, occasionally they need to … massage the figures slightly.
Truthfully, whilst many of us just know that an x,y or z engine or car will be inherently torquey or powerful, very few would be able to distinguish the characteristics of a ‘normal’ road car to any degree of accuracy. The general consensus is that you’d need to have a minimum of around 10% difference to actually feel it, unless your seat of the pants dyno is particularly well calibrated.
In general, talk regarding torque vs horsepower, will undoubtedly become a moot point in the future, as it will be replaced by one simple measurement: kW.
Forgetting all of the why’s and wherefores, electric power can deliver massive amounts of torque from standstill, meaning acceleration is always brisk, despite the weight penalty of having hundreds of laptop batteries glued to the chassis.
The balance between torque vs horsepower may very well be replaced with electric cars in the future.
In fact, a Tesla Model S P90D has just taken the record for an all-electric production car ¼ mile sprint, completing it in just 10.9 seconds. As a comparison, a Bugatti Veyron will do the same in 10.175 seconds. It really does seem as if electric power is the way forward, as the gap in performance in closing very, very quickly.
Whether it’s forced induction, long stroke vs short stroke, bore size, compression ratio or camshaft design, it all plays a part in changing the power characteristics of an engine. There is no simple answer as to what is best, so perhaps the simple question is: what suits you best?