We looked at engines that had upto three cylinders last week — this time, we’ll have a close look at the world’s most popular engine, the four-cylinder engine. Most cars (and performance motorcycles) possess a four-cylinder engine, and most of these four-cylinder engines arrange their cylinders in a single line.
The in-line arrangement helps bring costs down, because a single head is required for this kind of an engine. A modern small car will have a transverse engine, as it drives the front wheels. Motorcycles like the Suzuki Hayabusa and Yamaha R1 also place their engines transversely. Look under the hood of a taxi or a BMW, however, and you’ll find the engine is longitudinal, because it drives the rear wheels.
Four-cylinder engines usually fire two cylinders together — for example, the cylinders at the ends will have their power stroke together, and the two cylinders in the middle will have theirs simultaneously. This gives the engine a good torque curve, but these engines also tend to vibrate at high revs. Another limit that has been found through research is the displacement.
Upto two litres, an inline four has minimum vibration. Any more than that and a lot of technology begins getting involved to smoothen things out. The Honda Accord has one of the smoothest four-cylinder units around, and displaces 2.4 litres.
It keeps things fuss-free with the help of ‘counterbalancers’, which are shafts in the engine that rotate in the direction opposite to the engine’s rotation to counteract vibrations. If you look at engine displacements, manufacturers tend to use six-cylinder engines for displacements of 2.5 litres and above.
A perfect balance of cylinders?
Going back to the firing order of the cylinders, there’s one more type that isn’t very common. This order has each cylinder firing at regular intervals, one at a time.
This gives the engines perfect balance (although the two-litre rule still applies) but the torque output at low revs suffers. There’s an upside, however — the increase in torque is very linear. The new-for-2009 Yamaha YZF-R1 is a big deal because of this. They’ve switched from two cylinders together to firing them one at a time.
Chevrolet used to sell the Forester in India for a while — this car was basically a Subaru Impreza under the skin.
Subarus are known for their ‘boxer’ engines, which are much like the BMW R1200 GS engine, but with two more cylinders.
The ‘flat-four’ engine (it has 180 degrees between the cylinders) lies low in the engine bay, which lowers the centre of gravity and thus aids handling. Try to change a spark plug on a Forester, though, and you’ll wish you had two of you, to get the job done in half the time.
Engines that make you drool
‘V4’ engines are the same as V-twins, but with two more cylinders. They usually require one head per bank, but Lancia’s narrow-angle V4 engine needed only one head. This arrangement is quite popular with motorcycles.
Models that have this engine usually make the enthusiast drool.
The roster includes the Ducati Desmodici, Honda VFR, Honda RC 212V and the Yamaha V-Max. We’ve talked quite a bit about the four-cylinder engine — next week, we’ll move up the scale to more cylinders.