Fuel efficiency depends not just on how many cylinders your engine has, but also on how they’re usedindia Updated: Aug 27, 2009 16:02 IST
Over the last two weeks, we’ve been discussing engines, their layouts and the number of cylinders they use. The theme continues, but today we’ll deal with slightly more complex machinery.
Making the switch
Four-cylinder engines are usually vibration-free upto two litres in displacement, but when a manufacturer closes in on three litres, it makes more sense to switch to a six-cylinder format.
There are also five-cylinder engines running around — most notably, the current European Ford Focus ST has an inline (the cylinders are in a row) five-cylinder petrol engine, while the Volvo XC90 D5 sold in India has a five-cylinder diesel engine.
The Suzuki Grand Vitara XL7, the first SUV since the Gypsy that Maruti launched in India, had a 2.7-litre V6.
More cylinders means more power, but higher fuel consumption is one of the side effects, as any Accord V6 owner will tell you.
That car was the most powerful car manufactured in India: its 3.0-litre V6 produced 221 bhp, but that figure also showed up in the fuel bills, thanks to the four-speed automatic gearbox it came with.
Honda intends to rectify that reputation by launching the new Accord V6 some time next year, with something they call ‘Variable Cylinder Management’, a very clever piece of engineering that shuts off three cylinders out of six when the car’s brain determines that the extra power isn’t needed. Inline six-cylinder engines used to be very popular with lots of manufacturers till a while ago, because they have perfect balance (meaning almost no vibration) and they’re as simple as it can get thanks to the single head.
Inline six or V6?
A few years ago, Suzuki had showcased a very interesting two-wheeled concept called the Stratosphere, which had an inline six-cylinder engine. Now, however, BMW is almost the only big manufacturer who persists with this layout. Everyone else prefers a V6 layout, which reduces the engine’s length by arranging the cylinders in two banks (or rows) of three cylinders each.
Even Nissan switched the iconic GT-R’s engine to a V6, which disappointed many fans, until the new car was reviewed. Audi’s TT has what they call a ‘narrow-angle’ V6, because the angle between the banks of cylinders is so narrow it needs just a single camshaft to run the valvetrain.
The limit and beyond
Porsche is a unique manufacturer, because it has stayed with the ‘flat-six’ engine layout since its origin. This layout isn’t much different from Subaru’s ‘boxer’ engines; add two cylinders, bung the engine in the boot instead of under the hood, and Bob’s your uncle!
It isn’t as simple as that, of course, but the low centre of gravity contributes significantly to a Porsche’s legendary handling.
Rumours now abound that the flat-six engine has reached the limit of the amount of power it can put out reliably, and Porsche may look at more cylinders to go faster. Of course, if German performance specialists 9ff had anything to say about it, they’d show that the limit is far from reached.
They have a very exclusive (and appropriately expensive) car called the GT9 that begins life as a previous-generation 911 GT3, but ends up as a 1,000 bhp, rear-wheel drive monster that can get to 200 mph (320 kph) faster than a Bugatti Veyron can. Honda also runs flat-six engines, but on two wheels. The Valkyrie, especially the Rune, is one motorcycle that can be recognised instantly, as is the Goldwing.
Next week, we’ll take a look at the V8 engine, which powers cars like the Ferrari F430 and Ford Mustang GT.