Three-cylinder engines – why are we counting?

By Sally Dominguez, 13 May 2015 Car Advice

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Three-cylinder engines – why are we counting?

They say size doesn’t matter, it’s the way you use it. We take a look to see if this could apply to a three-cylinder engine.

*Warning: This content may contain perplexing, technical terminology. If symptoms of brain-fade occur, please click here.

An old interior decorating rule of thumb is ‘always buy items in pairs, because symmetry is harmonious’. Well it might surprise you to know but this rule also applies to your car’s engine.

Now, bear with us here while we explain... If you have pairs of cylinders in the engine – i.e., four-cylinder, a V6 or a straight-8 – there will be physical balance in the weight and the working of the engine. Cylinders are integral to an internal combustion engine, since they house the pistons and create the compression needed to create power. The balance of an even number of cylinders has always been the key to a smooth, rattle-free ride. Get it? No? Right, well read on…

So what is a piston, why is it inside a cylinder and why should you care? The piston is a snugly fitted disk or short cylinder moving up and down inside a larger cylinder against liquid or gas to ‘compress’ and give your vehicle power. You care because nobody wants to be a slug on the road and most people want decent acceleration off at the lights – right? And you care about cylinder count because a beautifully formed and minimal engine means better mileage, better front-crash safety and a fun, peppy drive.

If you mentioned a three-cylinder car to an old timer they might shake their head in disgust. In a three-cylinder engine, two out of the three pistons are moving up and down in the cylinders at once, which means it’s not even so when you’re driving it naturally produces a loping, unbalanced rhythm.

The three-pot engine is traditionally used in snowmobiles, motorbikes, tractors and trains where the intrusion of its uneven beat is offset by size, weight and pull advantages over larger engines. In cars, a ‘three-banger’ engine has typically signaled el-cheapo refinement (read “none”), poor performance and a generally lackluster driving experience. Hence why that old guy you were talking to before is shaking his head at you. That is, until now.

There are many reasons that car manufacturers are now revisiting the three-cylinder engine. Turbocharging technology has allowed car makers to reduce the number of cylinders in an engine while still increasing the power and performance by harnessing the exhaust to force extra air back into the cylinders (this is an explanation for another day). So, engineers foraging for better fuel economy and uncompromised performance are applying turbochargers and new balancing technologies to three-cylinders. The benefits of this is that in an engine with one less cylinder, the engine weights less, which ultimately leads to better handling and braking.

Most compelling of all, a good modern three-cylinder has a power to thirst ratio, meaning its engine is still powerful for its use in fuel – aka it’s better fuel efficiency and offers incredible bang for buck. Ford’s award-winning 1-litre three-cylinder EcoBoost engine for example, as found in the Fiesta Sport, has the same power-per-litre as the Ferrari 458. That means you can effectively fire off at the lights and still feel smug about your fuel bill. Seriously, in car talk that’s better than finding Max Mara jacket on sale, for half price.

The key is to find a three-cylinder engine that delivers the goods – something like the stalwart Mini Cooper D, with better performance and lower fuel figures, or the engaging and award-winning Renault Clio.

We spoke to Wheels road test editor, Nathan Ponchard who said a good three-cylinder engine is “satisfyingly thrummy and charismatic”. Top of his list sat the turbocharged Peugeot 308 as the best three-cylinder on the market, followed by Ford’s Ecoboost, and VW’s 1-litre non-turbo in the Up.

In business it’s called ‘rightsizing’ – understanding the optimum balance between economy and performance. As an efficient, lightweight nugget of power, the modern three-cylinder engine is increasingly relevant as the ‘rightsize’ solution to mid-sized and sporty vehicles. And car manufacturers agree as we see it popping up more and more.

It’s not the size that counts, it’s the way you use it.

 

GLOSSARY

Cylinders are a sealed enclosed chamber where the combustion happens.

Internal Combustion Engine: Put a small amount of high-energy fuel (like petrol) in a small enclosed space, light it and it will release a huge amount of energy as a gas. The internal combustion engine harnesses that energy to propel your car forward.

Pistons inside the cylinders move down the cylinder to let the air and gas in then push back up the cylinder to compress the fuel/air mix so that when the spark ignites it, the explosion is more powerful. That explosion drives the piston back down the cylinder and a crankshaft attached to the piston transfers that energy to the wheels via rotation.

Exhaust leaves the cylinder via the tailpipe or exhaust pipe when the piston ends its explosive journey and returns back up the cylinder, opening the exhaust valve.