Why is an engine said to be a 3L or 2L for that matter? I understand that V6 represents 6 cylinders, so I'm a little bit confused. I'm still busy with my motor studies.

  • Welcome to Motor Vehicle Maintenance & Repair! – Pᴀᴜʟsᴛᴇʀ2 May 30 at 17:58
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    a V6 is called that because it has its cylinders in 2 rows and there's an angle between the rows, so the engine looks like a V when seen from the front. This is to distinguish them from an inline engine, where all cylinders are in one row. – Hobbes May 31 at 7:30
  • I'd venture to say that there's also the aspect that it's more convenient than having to write 289in^2 or 4902cc – NitrusInc May 31 at 12:46
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    I'd like to add for disambiguation, that if the L is before the number, it means it's a Linear type engine, In Line Engine, or Straight Engine; and it's abreviated like: "L6", "L5", "L4" and alike. Example of said engines: BMW B58 "L6" in the BMW M240, GMC LLR "L5" in the GMC Canyon and Nissan SR20DET "L4" in the Nissan Silvia. – dmb May 31 at 15:10
  • @dmb I've always seen them written with an 'I' (presumably for 'inline'). I.e. I6, or I4. – tangrs Jun 1 at 8:36

When they put "3L", which stands for "3 litres", it is the approximate displacement of the engine. Displacement is the swept volume of all cylinders combined. Swept volume of the cylinder is if you look at the cylinder bore (area of the bore) multiplied by the stroke (distance the piston travels from top to bottom of the cylinder) multiplied by the number of cylinders.

It is usually annotated by:

V = πr²h * (# of cyls)

Where:

  • V is the volume (or displacement)
  • r is the radius (or 1/2 bore size)
  • h is the height (or stroke)

In most cars, when the displacement of the engine is "3L", it is usually very close to this, but not exact (say, 2997cc or 2.997L if you run the exact numbers).

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    And a "Capri 2.994S" badge wouldn't fit on the back as well as "Capri 3.0S" :) – Andrew Morton May 30 at 19:33
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    The displacement is typically just under the number because of regulations regarding taxes - in Germany you'd have to pay for a 2.3l engine if the displacement would be 2.201l. That's why the Honda diesel went from 2204 to 2197 or something in the refresh. – Arsenal May 30 at 21:53
  • @Arsenal - That may be true in Europe or other places, but they don't charge us taxes here (yet) in the States based on engine displacement. I'm sure it's a bleed-over here from places where it is based on it, though. – Pᴀᴜʟsᴛᴇʀ2 May 31 at 18:02
  • @Pᴀᴜʟsᴛᴇʀ2 yeah, I think so too, too much trouble building basically the same engine with a few cc difference just because there aren't the same rules in the US. – Arsenal May 31 at 19:21
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    @DividedByZero No because the definition clearly states swept volume of "all" pistons. As to why count all the cylinders, presumably it's a convention. And adding a constant coefficient doesn't really make much difference. – xiaomy Jun 1 at 17:12

Although Paulster2 excellently explained how the displacement is calculated, none of the answers adequately explained why the displacement matters.

The displacement is basically how much space burning gases have to expand. The more they expand, the more power they produce. So, displacement is related to engine's power output.

Unfortunately, if you create a bigger displacement engine, it is physically larger and thus has higher friction forces. This means that more fuel is lost to overcome the friction forces. Additionally, throttled engines such as most gasoline engines have higher pumping losses with larger displacement, further increasing fuel use.

So, there are three main effects of displacement:

  • The more displacement you have, the more maximum power
  • The more displacement you have, the more fuel the engine consumes for a given power output
  • The more displacement you have, the more expensive the engine is to manufacture due to using more materials and tooling time

There are of course some other effects as well. Some engine manufacturers have managed to make their engine rotate faster (more RPMs), meaning same displacement produces more power than most engines of the given displacement. Also, superchargers and turbochargers compress more air/fuel mixture into the cylinder, so this is also a way to obtain more power with the same displacement. Furthermore, some engine makers have went the opposite way, sacrificing maximum power in the interest of having more fuel efficiency by using the Atkinson cycle.

So, displacement used to be a measure of engine's power output, except due to turbochargers and superchargers it isn't anymore. Displacement today basically measures how much fuel you can afford to lose to overcome the frictional forces. If you have a 6-liter car engine today, it is just for showing off. A 2-to-3 liter high-revving twin-charged engine could perfectly well do most of its job today, at a cheaper price and lower fuel consumption.

It is interesting to see what happens to high-displacement engines when plug-in hybrid vehicles start to gain market share. It may be the case that the maximum acceleration burst power is produced by electricity alone, and the internal combustion engine just has to produce the average needed power at maximum efficiency.

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    Final paragraph - both plug-ins and convention hybrids produce maximum power with engine and electric motors working together. You're right that the ICE is sized for efficiency at mean power, but with enough headroom for a sustained burst. (I've owned both plug-in and conventional hybrids). – Toby Speight Jun 1 at 10:31
  • "...how much space the gases have to expand" is misleading. Displacement is a measure of how much fuel/air mixture is inducted. More mixture = bigger bang = more power – SiHa Jun 1 at 17:21
  • @SiHa: Good point: space to expand includes the volume past the upper limit of the piston. With a non-infinite compression ratio, there's some cylinder volume that isn't swept by the piston. – Peter Cordes Jun 2 at 3:57

L stands for Liter, the metric version of Cubic Inches.

Example. 5.7L = 350 cubic inches.

Simple math is to divide Cubic Inches by 61, or use one of the many internet conversion websites.

  • Please elaborate further regarding 3Liter. Why it is labeled 3Liter? – Thabo May 30 at 16:38
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    Because they use the metric system to label engine size (displacement). – Moab May 30 at 18:48
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    While liters are metric I disagree with your statement that it is the "metric version of cubic inches". The metric version of cubic inches is cubic centimeters. Liters are just a different way of representing displacement that is easier for most people to wrap their head around. – Jesse_b May 30 at 19:43
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    @Jesse_b: If anything, the litre is the metric counterpart to the fluid ounce. 1 litre = 1 cubic decimetre just as 1 fl.oz = 1.80469… oh wait, I forgot. Imperial units don't do that. – AkselA May 30 at 20:54
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    @SolarMike Liter to quart would make the most sense if you want them closest in size. Any of fluid ounce, cup, pint, quart, or gallon would work as a unit though. It's just that 1 liter is about 1.06 quarts, almost the same. It's more than two pints or a bit over .26 gallons. – Brythan May 31 at 0:46

Other folks have given good answers, but since you mentioned both the size (2L or 3L) and the cylinder configuration (V6) in your question, I just want to make one quick point on a possible confusion.

As you may know, there are engines which have all their cylinders in a line. This is known as an inline n engine. For example, an engine with 4 cylinders in a line would be an inline 4, or I4. This is a fairly common configuration in both cars and motorcycles. Some motorcycles have I3 engines.

Confusion could arise depending on how the letters are capitalized. Depending on the font, I4 (Inline 4) and 4l (4 liter) could look nearly identical; the only difference is the ordering of the letter and number.

Funny story as an example:

I have a 1992 Ford Ranger, with a 4L V6 engine (6 cylinders in a V configuration, with a total volume of 4 liters). In '92, Rangers were sold in 3 different sizes/configurations:

  • 2.3L I4 (4 cylinders in a line, with total volume of 2.3 liters)
  • 3.0L V6 (6 cylinders in a V, with total volume of 3 liters)
  • 4.0L V6 (what I have)

When I go to the local auto parts store, I tell them I have a "92 Ford Ranger". Their computer then gives them a list of the 3 engines listed above. If I just tell them that I have the "4 liter", they will often select the 2.3L I4 engine, because the I4 looks like 4l.

Moral of the story is don't let your eyes play tricks on you!

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    To add to this, often inline engines are actually abbreviated with an L (L4 for a 4-cylinder - linear 4?) – masospaghetti May 31 at 18:10
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    @masospaghetti - it's actually an "I4", the "I" (as in "eye") is for "inline" ... not an "L". If some manufacturer is putting an "L" before the 4, I'd not really know why ... not saying it doesn't exist, but I'd not have a reason for it. – Pᴀᴜʟsᴛᴇʀ2 May 31 at 18:13
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    One of the first results in a google search is link to Summit Racing's crate engine page, where they refer to inline-fours as L4's. And I think the 'L' refers to longitudinal. Confusing as heck regardless!! – Sam May 31 at 19:04
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    Longitudinal usually refers to a completely unrelated factor. An engine is transverse (cylinder bank perpendicular to the long axis of the car) or longitudinal (parallel) regardless of the cylinder layout. So if that's what it means, then they're not specifying the cylinder layout at all. Most 4 cylinders are inline, but some are horizontally opposed, and a few are Vs. On the other hand maybe they're just using longitudinal as another word for inline, which would be strange given longitudinal has another meaning in engine design. – nasch Jun 1 at 13:12

In Europe and especially Germany, fuel usage is stated as the amount of liters needed to drive 100km. Volkswagen presented the Lupo 3L model in 1999 to boast that it only needed 3 liters to drive 100km (equivalent to 78 miles per US gallon or 94 miles per Imperial gallon).

Perhaps this is what you are referring to. If not, it would be helpful to state on what cars you have seen this 3L.

  • It is not. If you ever bought a car and checked the spec you would know that engines are als having a displacement number. – TomTom May 31 at 8:48
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    What you say about the badge on the Lupo 3L is technically correct, but it also is the only car i can think of that has a badge referring to fuel mileage instead of engine displacement. So it isn't likely that Thabo is looking for this explanation unless he somehow sees Lupo 3L's driving around all the time. – MadMarky May 31 at 8:53
  • Very interesting historical factoid, @wurtel! – Sam Jun 1 at 3:55

In really simple terms, it is the amount of fuel/air mixture that is sucked/blown through the engine is one complete revolution of the crank. Bear in mind that the amount of power that can be extracted from fuel is finite, a larger engine capacity is one simple way to create a more powerful engine.

In reality there are many other complex factors that affect power output but rule of thumb is that a 2.0 litre engine will be less powerful than a 3.0 litre engine, especially if they're options within the same vehicle range.

  • That's not quite right, it's the volume the pistons move through. The fuel-air mixture expands when it's ignited, so would be substantially less than the displacement of the engine. – nasch Jun 1 at 13:13
  • Absolutely, plus there are two complete cycles per piston for each 4 stroke revolution. I was just trying to concoct a simple to understand description. I have seen bottom ends of engines used as pumping units by having their cranks spun and a custom plate in place of the head with oneway inlet valves and outlets on each cylinder. That’s probably where you’d see 2 or 3 litres “pumped” through. – Steve Matthews Jun 1 at 22:13

As a badge or emblem, this is a boast of the vehicle's power.

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    Don’t agree with this, a 3litre engine can produce a wide range of power : the jag 6cyl 3 litre engine started with some 120bhp and went to over 350 as fueling and ignition technology improved, so it states size but may not represent power... – Solar Mike May 30 at 20:32
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    @SolarMike: I think it still sort of holds true, while engine size does not directly correlate to power, it does affect the consumers opinion of power. However it often times likely is a boast of fuel economy (In cases where the badge is 1.2L or something similar) – Jesse_b May 30 at 20:53
  • There was the VW Lupo with a 3L badge on it, but that was the claimed l/100km and not the engine displacement... – Arsenal May 30 at 22:07
  • This is only remotely true with similar technology/design. F1 engines can kick out 800 bhp with 1.6 L – Nick T May 30 at 22:10
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    @JaccoAmersfoort I know all of that - you missed the point... see my first comment... and Rory's... – Solar Mike May 31 at 10:22

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