what do the liters represent when reading engine specs?

2.0L? 5.7L? Liters of what exactly? And, what is their significance?

(Automotive engines, specifically, but I suppose this can apply to any engine.)

The total displacement of the engine’s cylinders, i.e. the amount of liquid that would be pushed out of the cylinders as the piston rises in the cylinder. The liter is a unit of volume; the US equivalent is the cubic inch (1 liter = 61.024 cubic inches).

The engine’s power is somewhat dependent on its displacement – all other things being equal, a larger displacement engine will produce more power than a smaller one.

A litre is a measure of volume. Just like a cubic inch.

There are 61.024 cubic inches in a litre.

A 2.0 litre engine is a 120 cubic inch engine.

A 5.7 litre engine is a 350 cubic inch engine.

That help?

A different answer is that it’s the volume displaced by all of the pistons.

Say you’ve got a 4 cylinder engine with a bore of 8 cm and a stroke of 9 cm.

The volume of the engine is 4 x [symbol]p[/symbol] x (8/2)[sup]2[/sup] x 9 = 1800 cm[sup]2[/sup] = 1.8 L.

Ah, I see now.

Thank you.

What people have said before in here is true. Let me add one more little nitpick/addition - the type of engine can make a difference in terms of power comparisons. For example, in general a 2-stroke engine will produce more power than an equivalent 4-stroke engine of the same displacement, as it has double the power cycles. Also, a Wankel engine (Mazda RX-7, for example) doesn’t generally compare evenly with a 2-stroke or a 4-stroke engine in terms of displacement.

Alright, Anthracite, you’ve piqued my interest further. What is a Wankel engine and why wouldn’t it compare evenly with 2-stroke or a 4-stroke engine?

I’m assuming it has something to do with the fact that it is a rotary engine, since you mention Mazda…

A Wankel cycle engine is indeed a rotary engine. Rather than pistons, it has a triangularish turbine (or two, in the case of the RX-8’s engine) which produces a lot more power relative to its volume than an equivalent piston system.

It also uses a lot more gasoline/petrol to do it, however, I think because the rotation of the turbine doesn’t all transfer to the drive axle as efficiently as a piston system with separate camshafts does. But don’t quote me on that part.

Anyway, the point is a rotary engine is a lot smaller than a piston engine of similar output, but not really much more efficient.
The advantage, especially in a front-engined layout, is that a piston engine can be mounted further back, thus improving front/rear weight distribution. They also produce an extremely even power and torque curve, although Mazda turbocharges their rotary engines so this advantage is lost.

Incidentally, NSU was the first automaker to use the Wankel system for production engines, starting in the 60s.