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.
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)
- 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).
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.
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!
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.
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.