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Recently, after a discussion with friends, I stumbled over the engines available for a Fiat Panda Mk4 (yes, this is a "long story short" situation and now I'm stuck in a rabbit-hole). And I noticed something strange; a couple of days later it's still nagging me:

How can a 2-cylinder, 900 ccm have more power, more torque, a higher top speed, be quicker, and at the same time have less emissions and get better mileage than its 4-cylinder, 1,200 ccm counterpart?

The data I'm getting is from the car's Wikipedia page; as far as I was able to cross check, the numbers are accurate. In particular, I'm looking at the two 2011 petrol engines (to keep things fair), "0.9 TwinAir Turbo" and "1.2 Fire 8v".

  • The first is a straight-2 with 875 ccm that generates 63 kW, has 145 Nm of torque, with a top speed of 177 km/h, and does 0–100 km/h in 11,2 s. It emits 99 g of CO2/km and needs 4,2 l for 100 km.

  • The other is a straight-4 with 1,242 ccm that generates 51 kW, has 102 Nm of torque, with a top speed of 164 km/h, and does 0-100 km/h in 14,2 s. It emits 120 g of CO2/km and needs 5,2 l for 100 km.

Granted, some of the values differ only marginally. Others, on the other hand, are quite egregious discrepancies. How can the smaller, more "efficient" (for a lack of a better word) option outshine the bigger, "hungrier" sibling in basically every category?

Somebody suggested "it's the turbo; it does all the difference" (and I've seen questions answered on this platform, but the differences were far less pronounced). "Turbo" might very well be the reason, but then another question arises: Why would anyone want the 4-cylinder option? Why is it even offered as an option if it has zero advantages over the smaller one? What are the advantages of this particular bigger engine?

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  • Welcome to Motor Vehicle Maintenance & Repair! Dec 12, 2023 at 21:53
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    @JimmyJames 2 cylinders doesn't imply a 2-stroke engine.
    – Dan Mašek
    Dec 13, 2023 at 21:34
  • @DanMašek I figured something like that was coming. Is this a 4-stroke engine? There must be some advantage to having 4 cylinders, right?
    – JimmyJames
    Dec 13, 2023 at 22:02
  • @JimmyJames Can you imagine Fiat developing a new 2-stroke in 2011 and trying to sell that in a car in EU? Downsizing taken to the extreme.
    – Dan Mašek
    Dec 13, 2023 at 23:47
  • Regarding the bonus question at the end, people do seem to choose engines based on displacement rather than power or efficiency - and the displacement is normally what's shown on the back of a car in some form (my van OTOH has the horsepower and max gross weight displayed on the side). I did wonder if they also offered a turbocharged version of the 1.2l engine, but no.
    – Chris H
    Dec 14, 2023 at 9:14

1 Answer 1

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How can the smaller, more "efficient" (for a lack of a better word) option outshine the bigger, "hungrier" sibling in basically every category?

In a word: Turbocharging

Same reason why Richard Holdener built a Big Bang Motor out of a 4.8L engine which put out over 1200 hp, yet stock (naturally aspirated), it put out around 300 hp. A turbocharger (or turbo for short), basically makes a small engine "think" it's bigger. For every 14.7 lbs (1 bar) of atmospheric pressure (or boost) you can stuff into an engine using a turbo, you'll increase the horsepower versus the same engine which is running naturally aspirated by 100% (considered a rule of thumb ... your mileage may vary). For instance, if naturally aspirated an engine produces 100 hp, by adding 14.7 lbs (1 bar) of boost, the engine should now be making 200 hp. If you added 29.4 lbs (2 bar), it'd be making about 300 hp. This is true all the way up the scale ... as long as the engine is made to take it.

Why would anyone want the 4-cylinder option? Why is it even offered as an option if it has zero advantages over the smaller one?

It is usually cheaper and the engine will usually last longer, all things considered. A turbo adds complexity to an engine, and with complexity comes cost.

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  • A turbo also adds stress to the head, block, gaskets, and every other part of the engine and could, if not properly accounted for, cause premature engine failure.
    – FreeMan
    Dec 13, 2023 at 19:21
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    @FreeMan - You must have missed the part where I said "... as long as the engine is made to take it." Yes, you are absolutely correct. The engineer designing the engine needs to account for this stuff. Dec 13, 2023 at 20:39
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    @FreeMan "if not properly accounted for, cause...failure" you can always say that, about anything. Properly accounting for stuff is a main part of an engineer's job. There's almost as much that can go wrong in a naturally aspirated engine as in a turbocharged one; given same quality engineering, they will also be similarly reliable. (But the turbo one will be more expensive then.) Dec 13, 2023 at 21:18
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    A turbo...exhaust gasses go into the turbocharger and spin it, witchcraft happens and you go faster. - Jeremy Clarkson
    – Scooter
    Dec 13, 2023 at 22:40
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    @Scooter - Pretty much :o) Dec 13, 2023 at 22:57

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