Car engines 101 - what is the right engine for you?

"This car how many cc ah?"

That's often the first question I get from my parents when they get into a new car that I'm test driving. And in their mind, bigger cc is always better, smaller cc always indicative of an underpowered car.

30 years ago, that would be undeniably true. But these days, such a simple understanding of engine size as directly correlated to performance isn't quite as straightforward anymore.

Understanding engine capacity

We think of engines in terms of their size - 1.0-litre, 2.0-litre and so forth. However, that isn't a measure of the engine's physical size.

Without wanting to get overly technical, an engine's capacity, or more accurately its displacement, is a measure of the total volume of air and fuel being pushed through the engine by the cylinders when combustion occurs. This is measured in cubic centimetres (cc).

As such, a 1,000cc engine can displace one litre (1,000cc) of the air-fuel mixture, and a 3,000cc engine can displace three litres. Manufacturers thus label engines accordingly - 1.0-litre, 1.5-litre, 2.0-litre, etc.

An engine creates power through the process of the combustion of the air-fuel mixture. Subsequently, having more displacement means that the engine is able to generate more power.

This is why, traditionally, a bigger displacement naturally aspirated (NA) engine almost always means a more powerful engine.

Turbocharging trickery

The application of forced induction technology (including both turbocharging and supercharging) has fundamentally altered the traditional 'rules' about engine size and performance. Again, without wanting to get too technical, a turbocharger essentially forces extra compressed air into the engine.

With more air available, the turbocharged engine is thus able to generate more power compared to a NA engine of the same capacity.

But, what does this actually mean to the layman?
 

Well, put simply, the traditional understanding of a 2.0-litre engine being more powerful than a 1.6-litre engine being more powerful than a 1.0-litre engine may not be strictly true anymore.

Take for example the Mercedes-Benz CLA45. It has a turbocharged 2.0-litre engine that produces a mind-bending 416bhp and 500Nm of torque. Mercedes' own turbocharged 3.0-litre engine in its C43 model produces less power (385bhp). And, a Ferrari 360, which uses a NA 3.8-litre V8 engine, produces 394bhp.

With turbocharging, manufacturers have managed to extract extra performance from smaller engines. So, you shouldn't be so quick to dismiss smaller cars with 1.0-litre engines (we're seeing more and more of such models nowadays).

A Volkswagen Polo, with its turbocharged 1.0-litre engine producing 114bhp and 200Nm of torque, has similar performance to a Honda Civic 1.6, which has 123bhp and 152Nm of torque.

Size isn't everything.

Horsepower vs torque

So how do you judge an engine's performance, then? Here, it's not quite as simple as just engine capacity.

Two units of measurement always come up when describing engine performance - horsepower and torque. Trying to fully explain the difference between the two is a head-scratchingly difficult exercise, but I will persist to offer as simple an explanation as I can.

Torque is a measure of work done, and in the case of an engine it quantifies the rotating force produced by the crankshaft. Power is a measurement of the rate of work done. For cars, it is a mathematically derived value - horsepower equals torque multiplied by rpm.

The key thing to understand is this - when you get in a car and step on the accelerator, that surge that your feel, the so-called 'punchiness' or force of acceleration, is torque, not bhp.

This is generally why turbocharged engines tend to feel 'stronger; and 'more powerful' at lower revs, and tend to have higher torque figures compared to a NA engine of similar power. A turbocharged engine is able to generate more torque across a wider rev range.

And of course, the car's weight has to be taken into account. A lighter car would of course feel 'faster' than a heavier car with an identical engine.

So, take once more the aforementioned VW Polo and Honda Civic. The 1.0-litre Polo has notably more torque than the heavier Civic, and is thus quite a bit quicker from 0-100km/h (9.5 seconds compared to the Civic's 11.6), even though the Civic has more bhp and a larger capacity engine.

Again, size isn't everything.

Then tax, how?

For Singapore owners, there is the obvious question of money - how does engine size and performance relate to taxation?

In the past, the distinctions between engines were simple, and Singapore's taxation structure reflected that. Cat A COE is for 1.6-litre engines and below, and Cat B for anything more than 1.6-litres. Road tax is calculated based simply on the engine capacity.

Now, the COE categories have been adjusted to account for the changes in engine performance, too. Cat A COE is capped at 1.6-litre engines with a maximum of 130bhp, and Cat B is for cars above 1.6-litre capacity or 130bhp. The structure for road tax remains unchanged, based on engine capacity.

So smaller is better?

Generally speaking, a smaller capacity engine would incur lower taxes compared to a larger capacity engine. The logic behind it is simple - a smaller engine would use less fuel and produce fewer emissions.

This is why you see most manufacturers 'downsizing' engines to meet new emissions regulations while utilising modern technology to still deliver comparable or even higher levels of performance and efficiency.

As we've demonstrated, in today's day and age, smaller doesn't necessarily mean less powerful. Smaller engines also tend to be more economical, both to buy and to run long term. 

So when it comes to choosing the 'right' engine for you, engine capacity is but one of a few indicators of performance and capability, not the only one. In fact, looking at the engine's performance figures, both horsepower and torque, would give you a better indication of performance. 

That said, some drivers still prefer bigger capacity engines, whether it's the feel or sound of the engine or the fact that, yes, bigger engines can still deliver immense performance. As the saying goes, 'there's no replacement for displacement'. 

But remember, size isn't everything.

This article was first published in sgCarMart.