# what do the liters represent when reading engine specs? **URL:** \ **Category:** Factual Questions\ **Created:** [July 19, 2003, 5:07pm UTC](https://boards.straightdope.com/t/what-do-the-liters-represent-when-reading-engine-specs/189597 "2003-07-19T17:07:17Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![vandal](https://avatars.discourse-cdn.com/v4/letter/v/858c86/32.png) [@vandal](https://boards.straightdope.com/u/vandal)\ **Post date:** [July 19, 2003, 5:07pm UTC](https://boards.straightdope.com/t/what-do-the-liters-represent-when-reading-engine-specs/189597/1 "2003-07-19T17:07:17Z")
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.) ---
**Author:** ![3waygeek](https://avatars.discourse-cdn.com/v4/letter/3/e95f7d/32.png) [@3waygeek](https://boards.straightdope.com/u/3waygeek)\ **Post date:** [July 19, 2003, 5:20pm UTC](https://boards.straightdope.com/t/what-do-the-liters-represent-when-reading-engine-specs/189597/2 "2003-07-19T17:20:04Z")
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. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [July 19, 2003, 5:27pm UTC](https://boards.straightdope.com/t/what-do-the-liters-represent-when-reading-engine-specs/189597/3 "2003-07-19T17:27:35Z")
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. ---
**Author:** ![vandal](https://avatars.discourse-cdn.com/v4/letter/v/858c86/32.png) [@vandal](https://boards.straightdope.com/u/vandal)\ **Post date:** [July 19, 2003, 5:35pm UTC](https://boards.straightdope.com/t/what-do-the-liters-represent-when-reading-engine-specs/189597/4 "2003-07-19T17:35:19Z")
Ah, I see now. Thank you. ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [July 19, 2003, 7:01pm UTC](https://boards.straightdope.com/t/what-do-the-liters-represent-when-reading-engine-specs/189597/5 "2003-07-19T19:01:28Z")
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. ---
**Author:** ![vandal](https://avatars.discourse-cdn.com/v4/letter/v/858c86/32.png) [@vandal](https://boards.straightdope.com/u/vandal)\ **Post date:** [July 19, 2003, 8:30pm UTC](https://boards.straightdope.com/t/what-do-the-liters-represent-when-reading-engine-specs/189597/6 "2003-07-19T20:30:58Z")
> [@](#): > > \*Originally posted by Anthracite \* > \*\*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… ---
**Author:** ![Really\_Not\_All\_That\_Bright](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@Really\_Not\_All\_That\_Bright](https://boards.straightdope.com/u/Really_Not_All_That_Bright)\ **Post date:** [July 19, 2003, 8:41pm UTC](https://boards.straightdope.com/t/what-do-the-liters-represent-when-reading-engine-specs/189597/7 "2003-07-19T20:41:46Z")
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. ---
**Author:** ![Really\_Not\_All\_That\_Bright](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@Really\_Not\_All\_That\_Bright](https://boards.straightdope.com/u/Really_Not_All_That_Bright)\ **Post date:** [July 19, 2003, 8:45pm UTC](https://boards.straightdope.com/t/what-do-the-liters-represent-when-reading-engine-specs/189597/8 "2003-07-19T20:45:09Z")
Incidentally, NSU was the first automaker to use the Wankel system for production engines, starting in the 60s.