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Comparison: three-cylinder engines on test
The modern motoring era isn’t full of technological trends of which keen drivers can unreservedly approve.
Autocar

Given the chance, I suspect that most of us would take the start-stop starter-generators and electric power steering out of our new cars in a heartbeat. But the meteoric rise of the downsized, turbocharged three-cylinder petrol engine deserves an unqualified round of applause. This is efficiency innovation that we can all get behind.

Over the past three years, these engines have spread across European model ranges faster than any type of powertrain that I can remember. And standing in a car park near Brentwood in Essex in the early morning light, Andrew Fraser is explaining why.

Fraser is powertrain development manager at Ford’s Dunton Technical Centre and one of the key men behind the motor that started all this in 2012: the 1.0-litre EcoBoost. “It’s not just about weight or cubic capacity,” he says. “It’s got more to do with a combination of rotational balance, thermal efficiency, space efficiency and suitability for turbocharging.” Pay attention at the back: engineer talking.

“Three-pots have much less second-order vibration than four-cylinders,” he explains, “so they can sometimes do without balancer shafts entirely and can manage with shorter conrods than four-cylinder units, so they fit into a smaller space.

Having fewer cylinders for the same swept volume means you lose less energy as heat, and because you’ve got fewer exhaust pulses per crankshaft revolution, both turbocharging and cooling are also easier. So the efficiency gains can 
be made on several fronts. I’m not at all surprised that it wasn’t just us that realised it.”

Fraser and I are looking at the evidence of that realisation: five new cars from five different manufacturers, and as many different sub-sections of the market, all of which are powered by new-generation turbo triples launched over the past three years. At the extra-small end of the spectrum is Renault’s 898cc three-cylinder turbo, nestling neatly in the hindquarters of the new Twingo city car. At the larger end is BMW’s 1499cc unit, which powers the biggest and heaviest of our group: the BMW 218i Active Tourer MPV.
CONTINUE AT AUTOCAR.CO.UK
 

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I had two identical BMW motorcycles except for the engine. The K75 had 3 cylinders and the K100 had 4. The K100 was more powerful but was buzzy and felt less refined. The 3 cylinder K75 was silky smooth and the smoothest motorcycle BMW built at the time. My first experience with a 3 cylinder engine was with a friend's very smooth Suzuki GT550 two stroke in the 70s. I also really liked my 3 cylinder diesel farm tractor. I would buy a 3 cylinder car without hesitation.
 

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I would love one of those Ford or BMW powered vehicles.

I can attest that 4 cylinder (and smaller) engines have to be driven differently than other vehicles in order to get the great fuel economy that is there. I manage to average over 45 mpgs combined driving economy in a 1997 Escort - it takes time to learn a vehicle's (engine's) sweet spot - but once trained, these engines are amazingly efficient - and hitting 50 mpgs on the highway is no longer difficult but routine.

I bet I could get over 60 mpgs on the highway with a Ford or BMW three pot - it would be fun. I wonder what a diesel one would be like.
 

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I had two identical BMW motorcycles except for the engine. The K75 had 3 cylinders and the K100 had 4. The K100 was more powerful but was buzzy and felt less refined. The 3 cylinder K75 was silky smooth and the smoothest motorcycle BMW built at the time. My first experience with a 3 cylinder engine was with a friend's very smooth Suzuki GT550 two stroke in the 70s. I also really liked my 3 cylinder diesel farm tractor. I would buy a 3 cylinder car without hesitation.
A buddy and I purchased twin 1971 Kawasaki H1 500s, 60 claimed HP and rather peaky power, i.e. 6000 rpm is good, below is slow.
He moved on to a 750.
A friend had a 750 "Water Buffalo" Suzuki three which he just recently sold to a collector. One owner.

The 500 Kaws were fun to ride together. They'd almost match harmonic cycles but were just a bit out of synch, made for cool vibe/sounds on the road.
 

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I had two identical BMW motorcycles except for the engine. The K75 had 3 cylinders and the K100 had 4. The K100 was more powerful but was buzzy and felt less refined. The 3 cylinder K75 was silky smooth and the smoothest motorcycle BMW built at the time. My first experience with a 3 cylinder engine was with a friend's very smooth Suzuki GT550 two stroke in the 70s. I also really liked my 3 cylinder diesel farm tractor. I would buy a 3 cylinder car without hesitation.
your K75 had twin contra-rotating balance shafts and a lazy, slow engine - the K100 had none, and a solidly-mounted engine which accounted for the harsh high-frequency vibes typical of a high-comp four. I had a Waterbottle GT750 and it was silky smooth - because it was three low-comp TS250 trailbike engines with incredibly lazy port timing on a common and mega-sized flexible alloy crank-case; rubber-mounted at the front, which gave the frame the consistency of slightly limp spaghetti and accounted for their nickname of 'Flexiflyer'. They were great distance tourers, but if a Porsche was riding your rear fender in the twisties best get out of the way and not be a hero. Two stroke triples feel smooth because of no valvegear and resultant reciprocating noise and vibes of valves opening and closing.

I have a Triumph Speed Triple, 955cc fuel injected T595 model. It's a high-comp engine with peak torque at 3000 revs - rorty, is how I would characterise it. It too has twin balance shafts, yet still shakes and pulses at <3000rpm. Interestingly, the three-cylinder pulses are far less wearing than fours for some reason. You can ride all day without feeling pins and needles or discomfort, even though it's rougher. At times it eight-strokes, at times it shakes like a twin. But aurally and perceptibly it has a much more pleasant 'vibe'.

The difference to these turbo car mills is, they have lower compression, milder cam timing, smaller specific power from lower BMEP being premised on torque. My bike is rated [email protected] They use the turbo plus DI to boost low-end rather than high-end power. Short rods also lend to more smoothness - typical Japanese motor, but lower torque - hence again, the turbo works to put back what reducing the ideal 1.6 or 1.7:1 rod length/bore ratio which usually makes for more secondary vibes. A 120 degree triple has better primary balance but worse secondary than a 180 deg inline four, due to length of crankshaft creating rocking couples (the big-ends are offset by a long way). This produces shaking or rocking which is larger in amplitude but less severe-feeling, compared to the harsh high-freq vibes characterised by a four.

These cars also have large dual mass flywheels which smooth out the impulses. NVH control in these also relies on fluid-filled bushes and things like alloy engine cradle/subframes which are bushed - does nothing for longterm chassis integrity but a lot for smoothness. Watch them idle - the engine dances a lot more on it's mounts than a four.
 

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I had two identical BMW motorcycles except for the engine. The K75 had 3 cylinders and the K100 had 4. The K100 was more powerful but was buzzy and felt less refined. The 3 cylinder K75 was silky smooth and the smoothest motorcycle BMW built at the time. My first experience with a 3 cylinder engine was with a friend's very smooth Suzuki GT550 two stroke in the 70s. I also really liked my 3 cylinder diesel farm tractor. I would buy a 3 cylinder car without hesitation.
My Triumph's triple is a nice smooth engine, although it does have a balance shaft. I agree ... bring on the automotive triples!
 

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I have a 2008 Toyota Aygo, with a 1.0 liter three cylinder. These engines are quite course and have major vibration issues at idle. That said, in a small light 2300 lb city car I get fantastic fuel economy. I'll avg 35 mpg in the city, and well over 60 mpg highway if I don't drive more than 60 mph. For my needs, five mile commute to work in Finland, it's perfect. However the engine isn't well suited for highway driving, as I have driven it all the way up to Finnish Lapland, a distance of around 500 miles. :)
 

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Motorcycle manufacturers are adding three cylinders to their lineup, such as: Yamaha and MV Augusta. It's a nice combination for an engine as it has a bottom end of a v-twin and a top end of an inline-4. My Triumph Speed Triple with it pulls like a diesel from about 2,000 RPM all the way to the redline of 10,000 RPM, without any issues. Great engine for street and track really. I'm not sure how well that would translate to a car, but with a torque cure such as this one, it's hard not to see it's ups Font Tower Parallel Pattern Engineering
 

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Easy to make such claims now that turbocharging has reached a practical reality. Prior to that, the increased volumetric efficiency and lower piston speeds of more cylinders meant that 3 cylinder mills such as in the 1980s Geo Metro were less than common. The V8 and I4 were mainstream for good reason.
 
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