Fiat 500 TwinAir

9 Jul, 2010 3:54pm

New smaller two-cylinder engine gives 500 lower emissions and better efficiency.

Verdict

4
* Price: £13,000 (est)* Engine: 900cc, two-cylinder* Transmission: Five-speed manual, front-wheel drive* Power: 84bhp* Torque: 145Nm* 0-62mph: 11.0 seconds* Top Speed: 107mph* Economy: 68.9mpg* Emissions: 95g/km* Standard kit: Blue&Me USB connection, MP3-compatible stereo, air conditioning, seven airbags, 15-inch alloys* On sale: September

Size matters. And for Fiat, it's a case of the smaller the better with its new TwinAir 900cc two-cylinder engine.

On the outside, there's little to distinguish the two-cylinder Fiat from any other 500, aside from this new blue colour which debuts on the car. It's the same story inside, where retro oversized dials reminiscent of the original 500 meet the clever Blue&Me data logging system which analyses your driving and gives you tips on how to drive more efficiently.

Video: watch CarBuyer's video review of the Fiat 500

But as soon as you turn the ignition key, it's clear that there's a very different powerplant under the bonnet. Fiat describes the TwinAir unit as a manifesto for its latest engine technology. So as well as being smaller, it is the first engine to be developed from scratch to make the most of Fia's MultiAir system.

It uses electro-hydraulic control of the inlet valves, rather than a conventional camshaft, to manage the amount of air entering the engine. This allows more precise management of combustion, reducing fuel consumption.

As well as boosting efficiency, the managed air flow improves low-down torque, while the more constant flow of air keeps the small turbocharger spinning, pushing power up to 84bhp.

At idle, the engine chatters into life, making a noise similar to a diesel but with a more breathy character. It's quiet, especially in the cabin where you’d be hard pressed to notice that you weren't sitting in one of the other petrol units in the range.

But once you move off the sensation is quite different. Below 2,500rpm, the engine feels just like a conventional four-cylinder. It pulls surprisingly well too, helped by short gearing to make the most of the unit's power and 145Nm of torque. The gear ratios are widely spaced, which means you need to use the engine revs more to make good progress, especially if you press the fuel-saving ECO button which restricts torque to 100Nm.

But above 2,500rpm the soundtrack changes, sounding more like a small motorbike than a car and in tune with the Fiat's original 500 which was also powered by a two-cylinder unit.

What's surprising is that although the engine note is unfamiliar, the refinement is impressive. Thanks to a balancer shaft which counterweights the action of the cylinders, vibrations are well isolated. Were it not for the characterful soundtrack, the unit feels similar to an equivalent 1.4-litre four-cylinder unit.The icing on the cake is fuel economy of nearly 70mpg and thanks to CO2 emissions of just 95g/km, owners taking delivery later this year will be able to enjoy road tax-free motoring.

Rival: Smart ForTwo
As well as a downsized engine, the Smart is a downsized car. But its tiny proportions make it easy to negotiate city roads, while the unique styling is more modern than the 500's retro chic. Thanks to a clever Mitsubishi-sourced three-cylinder engine, the Smart runs the Fiat close in the fuel sipping stakes, but it's expensive and only has two seats.

Disqus - noscript

Do you intend to test engines reliability on all kind of roads and conditions? Otherwise sounds lovely and petrol

Do you intend to test engines reliability on all kind of roads and conditions? Otherwise sounds lovely and petrol !

Interesting engine but £13K?? Forward looking engine in a backward looking car.

Will be even better (and hopefully cheaper) in the 2011 Panda.

It would sure make a nice 3 cylinder engine. It should make more than 3/2 the power of the twin as a three cylinder is naturally balanced not needing any help that has rotating weight and makes friction.

It sould drag a good deal more iron around and still get 40 mpg with low CO2 emissions.

GC

AFAIK, the only engines that are naturally balanced are straight sixes and V12s (i.e. 2 x straight six).

Inline 2s with no balancing are almost unusable, but bearable with balancing. One cylinder is always heading in the opposite direction to the other, causing large amounts of vibration.

Inline 3s vibrate from one end to another, but can be smoothed with a balancer shaft. Even then, you wouldn't normally describe them as smooth.

Inline 4s vibrate with secondary order force, which isn't too bad until greater than 2 litres, when balancer shafts are required to damp the excess vibration.

Inline 5s suffer end to end vibration as a 3 pot does, also fixed with a balancer shaft.

Inline 6s balance themselves, and so are "perfect". Turn it into a V12 and you have 2 balanced heads, with twice as many firing pulses, making it even smoother.

V6s, V8s and V10s have basically the same problems as the inline versions (2x3 pots, 2x4 pots or 2x5 pots) but additional issues depending on what angle is used between the banks.

In a sense, this is all academic, as clever engineering can make almost any engine configuration quite refined, which is what Fiat seems to have done with this.

Oilburner is right of course, but what about the old ring-a-ding three cylinder two strokes like Saab used? They were I believe as well balanced as a six cylinder four stroke.

Imagine a turbo charged three cylinder two stroke. No nasty crankcase compression and oil-in-petrol and twice the number of power strokes. I'm sure that the emissions could be controlled these days.

Why not?

I love the new fiat convertible 500. This car is very girly, small and practical, the perfect city car especially for busy cities. My mum just bought one and she says she feels very safe driving it, great for the summer as I love to have the roof down.

"Inline 2s with no balancing are almost unusable, but bearable with balancing. One cylinder is always heading in the opposite direction to the other, causing large amounts of vibration. "

Last time I checked, this was true for 2-stroke; in this 4-stroke design if you want even firing intervals you need an ignition every half cycle ie every turn of the engine, and therefore the two cylinders are always heading in the SAME direction. Which further reinforces your statement of the need for counterweight on the crankshaft and a balancer shaft, as well as one hell of a flywheel.

Hmm yes that's mostly true, but it depends how they've done it really. They may have offset the crankshaft to help balance, but leaving an uneven gap between firing - so they don't quite get to TDC at exactly the same time. I believe there is some trade off between getting the right crank angle to improve primary balance but at the cost of secondary balance. Obviously the balancer shaft helps manage this compromise.

Ultimately, I suppose all that matters is how it actually drives on the road. Given that the good old straight 4 is actually one of the worst (natural) configurations and yet the most popular set-up, theory always plays second fiddle to practice!

Either way, you can certainly smooth the engine out, but the aural pleasures of >4 cylinders aren't as easily engineered in! :)

I was hoping this was going to be horizontally opposed like half a porsche or subaru. wouldn't need balancing then.

Just about to get rid of mine after just over 2 years. fed up with all the niggly little faults, and the terrible bone shaking ride. Interesting the article mentions Blue and Me - mine has never worked properly since new and theyve bene unable to fix it. 3rd year dealer warranty isn't worth the paper it's written on. The second worst new car purchase I ever made- the first was the Grande Punto!

@ Oilburner> "the only engines that are naturally balanced are straight sixes and V12s (i.e. 2 x straight six)."

Come again. The only 'Naturally' balanced engines are 'opposed' engines. VW, Porsche, Subaru, and BMW, Honda Gold Wing bikes, and a lot of aircraft engines just to name a few of the 'boxer' engines.

Seems like a lot of people above are confusing primary balance, secondary balance, rocking couples and firing intervals... Fiat is 360 degree crank, giving primary inbalance, requiring correction by twin conta-rotating engine speed balance shafts to correct. Secondary forces will be approx half those of an in-line four (depending on conrod length to stroke ratio). Firing interval will be even and 360 degrees (once per revolution). Therefore, any vibration issues would most likely be torsional, causing 'chuggle' in the driveline at resonant frequencies, although playing about with the various rotating inertias during design phase, Fiat's engineers will likely have rendered these unnoticeable..

Sorry, above should read "single contra-rotating engine speed balance shaft".

Although broadly positive there are odd contradictions in the reports of the various publications which have tested the TwinAir. Auto Express has it about right. The car is refined, characterful and surprisingly quick. Its sound track is unusual but not intrusive. You need time to learn its foibles but, once mastered, you discover a Jekyll and Hyde car. In Normal Mode it revs freely and zips about with verve. Economy suffers but rarely to the extent that some writers have claimed. Choose Eco Mode, observe the shift indicator and make every use of Stop-Start and you will be rewarded with pleasing economy. My car is not run in but, driven sympathetically, will easily top 65 mpg over mixed roads. Factor in free road tax, free in the London Congestion Charging Zone and negotiated insurance on par with the much slower 1.2 and you have a great package. The premium over the 1.2 is not justified but I consider it money well spent. Neither of my Fiats have been unreliable. Service is patchy but improving. There are quicker and more economic versions of the TwinAir engine in the pipeline but this encapsulates the two. Fun or real economy. According to your mood; you choose.

Ive driven a 500 tiwn air for a couple of days and I have to say I am impressed, the 900cc turbo unit is a revelations, ok at tick over it sounds like a bag of nails but once your underway the engine actually sounds kind of fruity and with ample power to keep up with city traffic its no slouch. Once unleashed on the open road the 500's chassis and this engine make a delightful choice, ok you aren’t going to want to hoon about all day but a quick blat cross country would put a smile on your face especially when you then check how little fuel you’ve used.

Key specs

This new engine takes getting used to, but it's worth the effort. Yes, it needs to be worked harder than a larger unit, but around town, where this car is designed to be used, the engine isn't out of its depth. The sound may drone a little on the motorway, but in the cut and thrust or urban traffic, the revvy motor only adds to the 500's already impressive character. Factor in low running costs and you're looking at a very appealing city car.

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