A few years ago I stumbled across an interesting article at AutoZine about Engine Smoothness and the levels of harmonic balance inherent in various internal combustion engine designs.
I've always been interested in driving different kinds of cars to see what they're like, and this article inspired me to take a survey of the various engine configurations I've been lucky to sample.
Particularly, it made me more aware of the supposedly "naturally balanced" configurations: straight-6, V12 and all horizontally opposed "boxer" engines. In theory, these configurations are less susceptible to harmonic vibrations, making them potentially less complicated, more reliable and able to rev higher.
In reality, size, packaging, bearing configuration and other factors determine the success or failure of a given engine design. But the engineering side of my brain likes to consider the inherent rightness of an idea, however impractical, just like it considers the class A triode amplifier a design of inherent rightness.
So down to business: which of these have I driven? As it turns out, for a car guy, I haven't been behind the wheel of the diverse selection of vehicles I'd like. 15 years of living in the urban jungle can do that. But it's not a bad selection. To date I've experienced:
1 and 2 cylinders (scooters and motorbikes)
4 cylinders (inline and boxer)
6 cylinders (I6, V6 and flat 6)
8 cylinders (V8)
12 cylinders (V12)
Add to that turbo and diesel variants, along with front-wheel drive, rear-wheel drive and all-wheel drive.
Still to do: 3, 5 and 10 cylinders, Wankel rotary, supercharged and hybrid/electric.
My impression so far is... there's no clear winner.
Sorry for the letdown. As I suggested earlier, there's more to the performance of the engine than the basic configuration.
The boxer 4 ought to be an inherently good engine. But anyone who's driven a 36 HP VW knows that it's not breaking any speed records and has an unforgetable — if not entirely rhapsodic — clatter as it rambles down the road. The Porsche 356/912 variant was a step in the right direction, but still compromised in many ways by the basic design.
On the other hand, Subaru has done interesting things with the same configuration, building engines legendary for toughness and longevity, and winning the World Rally Championship along the way.
The inline-4 concept, on the other hand, is deeply flawed on paper — at least as far as harmonic compensation is concerned — and yet seems the realm of wonderfully fun engines in practice. From the Ford cross-flow (and its Cosworth variants) to the lengendary BMW M10 (1200+ HP in turbocharged F1 tune) to Honda and Toyota's peaky variable-cam engines to Porsche's 944/968 engines, all great stuff on the road.
I'm partial to inline-6 engines. There's a long history of straight-6 engines in racing, touring and sports cars, and both BMW and Mercedes built solid and enduring repuations on this engines. Smooth, powerful and reliable.
Horizontal 6? See: Porsche. Plenty has already been said about this, by folks with better pens than mine. Legendary.
But now let's skip ahead to my all-time favorite: the V12. Also legendary, and for good reason. On paper it's neatly balanced, powerful, smooth and a tour de force of Swiss-watch engineering and construction. Truly beautiful, and usually installed within the flanks of swoopy, racy bodywork. Typically we think: Ferrari.
I had the opportunity to spend an afternoon in a V12-powered BMW 760i and it was exhilarating. The sound is sublime, from whisper quiet tick-over to full-throttle roar. And even pushing along 2 tons of luxurious leather, aluminum and steel, dipping my foot well into the throttle pushed me back in the seat. And that roar. Did I mention the roar?
Some of these engine configurations are a bit more esoteric. Where do you find them?
2 cylinder: motorcycles, of course, but also the Honda N600 and Mazda R360. Otherwise you're going to have to find an Morgan 3-wheeler or other vintage cyclecar.
3 cylinder: Smart FourTwo. In Europe, there are several models from Opel, Renault, Toyota and Ford, among others, with fuel-sipping 3-cylinder engines. The 1-liter EcoBoost is supposed to show up in a US-bound Ford Fiesta.
V4: Lancia. Saab. And motorcycles, of course.
5 cylinder: straight-5 engines are commonly found in Audi, Volvo and VW cars, and Mercedes built a 5-cylinder diesel. The fact that I haven't driven one is kind of alarming.
10 cylinders: Audi S/RS6 and S8, BMW M5 and M6, Dodge Viper, Lexus LFA, Lamborghini Gallardo and Porsche Carrera GT. The VW Toureg and Phaeton had V10 turbo diesel options. Less luxurious: Dodge Ram pickups and some Ford trucks have V10 engine options.
Wankel rotary: Your choice is pretty much Mazda, and the RX-8 is now no more, ending the long, proud, buzzy history of production rotary-engined cars.
I had no idea 3-cylinder engines were making such a comeback.
Want to find out more? Take a look at Car and Driver's The Physics of Engine Cylinder-Bank Angles and this interesting discussion of the Harmonics In The L Series In-line 6 Cylinder Engines.