# Why do liters equate to engine power? **URL:** \ **Category:** Factual Questions\ **Created:** [July 23, 2002, 2:47pm UTC](https://boards.straightdope.com/t/why-do-liters-equate-to-engine-power/120378 "2002-07-23T14:47:18Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![bernse](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@bernse](https://boards.straightdope.com/u/bernse)\ **Post date:** [July 23, 2002, 2:47pm UTC](https://boards.straightdope.com/t/why-do-liters-equate-to-engine-power/120378/1 "2002-07-23T14:47:18Z")
YEAH! Without seeing your post, I’ll give the obvious answer. They don’t. They equate displacement, nothing more. 350cu-inch = 5.7L 305 = 5.0L 300 = 4.9L And the ever tricky Ford 302 = 4.9L (although for doctored the numbers to 5.0L) etc, etc Is that what you were looking for? ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [July 23, 2002, 2:50pm UTC](https://boards.straightdope.com/t/why-do-liters-equate-to-engine-power/120378/2 "2002-07-23T14:50:19Z")
> [@](#): > > Why do liters equate to engine power? They don’t; they equate to displacement. Of course, there’s a correlation between displacement & power, but I’ll leave that to the gearheads to explain… ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [July 23, 2002, 2:53pm UTC](https://boards.straightdope.com/t/why-do-liters-equate-to-engine-power/120378/3 "2002-07-23T14:53:47Z")
## Dang Board hosed my post…here it is: I’ve never understood why the amount of oil my car holds should in some way indicate the power of the engine under the hood of my car. You often see car companies touting that _they_ have a 3.5 liter engine in their car while their competitor merely has a 3.2 liter engine. Why the heck should this matter? If it’s such a marketing point why don’t car companies just add a larger oil pan to their car so they can say they’ve got a 5 liter engine (or whatever)? ## I’m obviously missing something here so what’s the deal? Upon seeing **bernse’s** post why does displacement relate directly to liters? Why can’t I just install a larger oil pan? ---
**Author:** ![ski](https://avatars.discourse-cdn.com/v4/letter/s/bbe5ce/32.png) [@ski](https://boards.straightdope.com/u/ski)\ **Post date:** [July 23, 2002, 2:55pm UTC](https://boards.straightdope.com/t/why-do-liters-equate-to-engine-power/120378/4 "2002-07-23T14:55:34Z")
Liters are a measure of displacement. Displacement is essentially the “volume” of the engine. The bigger the displacement, the bigger the engine. The bigger the engine, “generally” the more power you can get out of it. If you take the area of a piston, multiplied by the distance it moves each stroke, multiplied by the number of cylinders, you get the displacement. Lots of other things go into making an engine powerful, which is why displacement vs. power doesn’t always make sense. ---
**Author:** ![Ringo](https://avatars.discourse-cdn.com/v4/letter/r/779978/32.png) [@Ringo](https://boards.straightdope.com/u/Ringo)\ **Post date:** [July 23, 2002, 2:56pm UTC](https://boards.straightdope.com/t/why-do-liters-equate-to-engine-power/120378/5 "2002-07-23T14:56:22Z")
To borrow from [How Stuff Works](http://howstuffworks.lycoszone.com/question395.htm): > [@](#): > > \*\*I would like to increase the horsepower of my car’s engine. What’s the best way to do this? \*\* > Increase displacement - More displacement means more power because you can burn more gas during each revolution of the engine. You can increase displacement by making the cylinders bigger. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [July 23, 2002, 3:01pm UTC](https://boards.straightdope.com/t/why-do-liters-equate-to-engine-power/120378/6 "2002-07-23T15:01:13Z")
Ok…everyone’s on about displacement. I assume since they use two different measures that liters may equate to displacement but it is telling you something more (or different) than how many cubic inches your engine has. Is that a fair assumption (understanding the dangers of assumptions)? If so _exactly_ what is liters measuring? How many liters of liquid can fill X-cubic inches or how much oil your car hold or the recommended amount of milk you should buy on each trip to the store in your new car? ---
**Author:** ![bernse](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@bernse](https://boards.straightdope.com/u/bernse)\ **Post date:** [July 23, 2002, 3:03pm UTC](https://boards.straightdope.com/t/why-do-liters-equate-to-engine-power/120378/7 "2002-07-23T15:03:56Z")
Has nothing to do with the oil capacity of your car. It is more the “combustion” capacity. Ski gives you the basic definition. ---
**Author:** ![Ringo](https://avatars.discourse-cdn.com/v4/letter/r/779978/32.png) [@Ringo](https://boards.straightdope.com/u/Ringo)\ **Post date:** [July 23, 2002, 3:06pm UTC](https://boards.straightdope.com/t/why-do-liters-equate-to-engine-power/120378/8 "2002-07-23T15:06:24Z")
A liter of displacement equals about 60 cubic inches of displacement. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [July 23, 2002, 3:11pm UTC](https://boards.straightdope.com/t/why-do-liters-equate-to-engine-power/120378/9 "2002-07-23T15:11:34Z")
I don’t know why but I somehow missed **ski’s** post which answers much of what I was asking. Still, part of my question holds. Why bother labelling things in liters if it is simply another way of saying displacement? If you’ve got a 305 cubic inch engine why not just say that instead of tossing 5.0 liters in to confuse the issue (or vice-versa)? ---
**Author:** ![bernse](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@bernse](https://boards.straightdope.com/u/bernse)\ **Post date:** [July 23, 2002, 3:22pm UTC](https://boards.straightdope.com/t/why-do-liters-equate-to-engine-power/120378/10 "2002-07-23T15:22:51Z")
Just to screw you up! 🙂 The same reason they say my motorcycle is 1200CC instead of 1.2L. IMHO you’ll find as the Metric system gets used more and more “unofficially” in the US it’ll be more common to see the Metric displacement being used. As well, with the older motors from the 60s and 70s, they were always known in cu[sup]3[/sup] so not to confuse people into thinking they were different engines, they kept giving the discriptions in inches. However, since most of those engines are no longer in production for use in new vehicles, it doesn’t make much of a difference. Besides, as Crafter\_man mentioned, there is more to horsepower ability than strictly displacement. Say, a 3L engine can make as much power as an old 5.7L engine, but an old timer might be still thinking “their ain’t no replacement for displacement” which is “more or less” false nowadays. So lets start measuring displacment by a different unit so we don’t lose sales. Of course, this last bit is just a bit of a guess 🙂 ---
**Author:** ![Frank\_2](https://avatars.discourse-cdn.com/v4/letter/f/8c91f0/32.png) [@Frank\_2](https://boards.straightdope.com/u/Frank_2)\ **Post date:** [July 23, 2002, 3:24pm UTC](https://boards.straightdope.com/t/why-do-liters-equate-to-engine-power/120378/11 "2002-07-23T15:24:53Z")
Speaking as a part-time car hobbiest: Liters, cubic inches, CCs, they all mean the same thing: combustion volume of all the cylinders, or displacement. I can’t see any reason for using one over the other. **Whack-A-Mole** , the liters of your engine have no bearing on the oil capacity. Like **ski** touched on, the displacement also does not have a _direct_ corellation with the horsepower. A Formula 1 car can have as little as a 3 liter V-10 that pushes 800hp. Meanwhile the Dodge Vipe has a 8 liter V-10 that makes around 500hp. (numbers taken from [http://members.fortunecity.com/carstats/](http://members.fortunecity.com/carstats/) ) ---
**Author:** ![cjb](https://avatars.discourse-cdn.com/v4/letter/c/a4c791/32.png) [@cjb](https://boards.straightdope.com/u/cjb)\ **Post date:** [July 23, 2002, 3:36pm UTC](https://boards.straightdope.com/t/why-do-liters-equate-to-engine-power/120378/12 "2002-07-23T15:36:09Z")
Litres are the european measurement for cubic inches. They both refer to the combustion chamber piston displacement (swept volume), which is an easy single figure indicator of engine size. Though increasing displacement is one way to increase power it is usually quite an inefficient way of doing this. American cars often have large engines to get more power, and put up with inefficient combustion, but what you really need is a bigger, better explosion, and to get that you need more fuel and air. More fuel is easy to provide, but it gets quite difficult to put lots of air into a combustion chamber rapidly, and this is usually the limiting factor. This is why high-performance cars often have huge air intakes and trunking under the bonnet. Turbo-chargers also perform this function of feeding more explosive mixture into the combustion chamber. Just pouring in more air and fuel may still not get a large explosion - it might even be counter-productive. You need to look at how the explosion occurs, and arrange for it to happen most completely. You will find this sort of technology in lean-burn engines, which give a win-win situation, high power and low emissions. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [July 23, 2002, 3:38pm UTC](https://boards.straightdope.com/t/why-do-liters-equate-to-engine-power/120378/13 "2002-07-23T15:38:53Z")
a liter is about 61 cubic inches ---
**Author:** ![bcullman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bcullman/32/8207_2.png) [@bcullman](https://boards.straightdope.com/u/bcullman)\ **Post date:** [July 23, 2002, 4:38pm UTC](https://boards.straightdope.com/t/why-do-liters-equate-to-engine-power/120378/14 "2002-07-23T16:38:24Z")
> [@](#): > > \*Originally posted by Whack-a-Mole \* > \*\*I don’t know why but I somehow missed **ski’s** post which answers much of what I was asking. Still, part of my question holds. Why bother labelling things in liters if it is simply another way of saying displacement? If you’ve got a 305 cubic inch engine why not just say that instead of tossing 5.0 liters in to confuse the issue (or vice-versa)? \*\* There must be some misunderstanding here. When people say cubic inches instead of liters, they are merely trying to put it into a term (cubic inches) that you are more familar with (instead of cubic centimeters, which transate into liters). But besides that they are exactly the same type of measure measurement - they both measure volume. Why the change? Although the american public doesn’t use the metric system, almost all major industries these days to to better compete and trade with the world market. Thus, the auto industry, even the American auto industry, uses the metric system. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [July 23, 2002, 5:38pm UTC](https://boards.straightdope.com/t/why-do-liters-equate-to-engine-power/120378/15 "2002-07-23T17:38:54Z")
Think of it this way. Your engine is really just a series of controlled explosions. The way it works is that a mixture of gasoline and air is sprayed into a cylinder, then the piston comes up and a spark is used to explode the gasoline/air, forcing the piston back down. The total displacement is the total space for the air and gasoline inside the cylinders (before the piston comes up). All other things being equal, a bigger cylinder is going to hold more gasoline/air, and make a bigger boom, which means more power. As others have pointed out, all other things are not necessarily equal, so it’s possible to have a smaller engine have more horsepower. As I recall, liters really came into use in the 70’s when the smaller more fuel efficient cars were introduced. You couldn’t really brag about your massive awesomely powerful 180 cubic inch engine to the American public who was used to a 350 cubic inch engine being massive and powerful. But if you called it a massively powerful 3.0 liter engine, then the American public had no idea what you were talking about and only listened to the words massively and powerful. Similarly, engines used to be advertised by the number of cylinders they had, because let’s face it an 8 cylinder engine is basically a 6 cylinder engine with 2 more cylinders added on, so it’s got that much more power. Obviously under this system no one wants to advertise a 4 cylinder engine because it’s only half of an 8 cylinder engine so it looks puny and weak. Instead they advertise it as a 16 valve engine, which if you do the math simply means it has 4 valves per cylinder (2 intake and 2 outlet valves, this is where the gas/air and exhaust gasses after combustion go in and out of the cylinder). One of the worst uses of liter was during the gas crunch when a lot of gas stations changed their prices from dollars per gallon to dollars per liter. They even supplied little conversion charts for people who asked (and sometimes these were intentionally printed wrong), but people who were good at math figured out quite easily that they were actually charging a lot more per gallon than their competitors (who were still using price per gallon). ---
**Author:** ![av8rmike](https://avatars.discourse-cdn.com/v4/letter/a/edb3f5/32.png) [@av8rmike](https://boards.straightdope.com/u/av8rmike)\ **Post date:** [July 23, 2002, 6:04pm UTC](https://boards.straightdope.com/t/why-do-liters-equate-to-engine-power/120378/16 "2002-07-23T18:04:22Z")
[units geek mode] My truck has a massively powerful 466.6335 teaspoon engine. [/units geek mode] Oh, who am I kidding. Units geek mode can never be disabled. **Whack-a-Mole** , it all just goes back to the decades-long effort to wean us off our much-loved system of units. ---
**Author:** ![Joe\_Cool](https://avatars.discourse-cdn.com/v4/letter/j/ecb155/32.png) [@Joe\_Cool](https://boards.straightdope.com/u/Joe_Cool)\ **Post date:** [July 23, 2002, 7:48pm UTC](https://boards.straightdope.com/t/why-do-liters-equate-to-engine-power/120378/17 "2002-07-23T19:48:20Z")
To elaborate a bit on engineer\_comp\_geek’s post, here’s my backyard mechanic’s “ **Internal Combustion 101 For The Total Beginner** ”: Engine displacement is the amount of fuel/air mixture that can be sucked into the engine and burned on each complete combustion cycle (2 complete revolutions in the standard 4 cycle engine). This is calculated by taking the total volume traversed by one piston and multiplying by the number of pistons. Example: Let’s say your v8 has pistons with a 4.050" bore (diameter) and a stroke (distance traveled) of 3.780". That means one piston’s total displacement is the volume of a cylinder 4.050" x 3.780" or 48.70 cu. in. So your engine would have total displacement of 48.70 x 8, which is 390 cu. in., or about 6.4L. And it would probably be a Ford. 😃 In other words, your normally aspirated (no turbo, etc) 390 v8 burns approximately 390 cubic inches (6.4 liters) of fuel/air mixture at the current air pressure and temperature every 2 revolutions. Burning more fuel = more power, obviously. Since a bigger engine can suck in and burn more fuel (having more displacement), it makes more power. This is overly simplified. There are a lot of things that can affect your power. One of the biggest ones is the size of your carburetor (or fuel injector) and intake manifold. Smaller opening means less air can get through. A bigger intake is sort of like making your throttle open wider. More air and fuel can get through, so your engine burns more and makes more power. Air moves into the cylinders at a high speed. So if it’s timed well, simple inertia will force more mixture in at slightly higher pressure, creating more power. Turbochargers and superchargers do the same thing: they force more mixture into the cylinders mechanically (also creating higher compression), which makes even more power. The boost is measured in p.s.i. If your engine usually sucks in 2 liters at 14p.s.i. (standard pressure at sea level) and your turbo adds 8 pounds of boost, then you’re burning over 50% more fuel, and getting (in an ideal world) over 50% more power. Which is the same as having a bigger engine, but without the added weight and size. But the old adage _is_ true. There really is no replacement for displacement. Nothing makes more power except burning more fuel. If it weren’t so, tractor-trailer rigs and large machinery wouldn’t use large engines. Big engines with big cylinders make big torque, which is necessary for moving big things. Small engines can make a lot of power, but they are more delicate and more expensive than big ones, and don’t make as much torque. One of the main reasons they are used for racing (aside from speed limiting factors) is that smaller parts have less mass and can move faster. That means an engine can rev higher (the high pitched whine that Indy or F1 cars make, for example. Indycars hit their power band at around 10,600 rpm). Anyway, I’ve rambled enough. Sorry for taking up so much space. ---
**Author:** ![Enola\_Straight](https://avatars.discourse-cdn.com/v4/letter/e/dec6dc/32.png) [@Enola\_Straight](https://boards.straightdope.com/u/Enola_Straight)\ **Post date:** [July 23, 2002, 7:51pm UTC](https://boards.straightdope.com/t/why-do-liters-equate-to-engine-power/120378/18 "2002-07-23T19:51:27Z")
I always found that 1 Liter=61.4 cubic inches as a good conversion factor. Displacement Is a strong indicator of torque. (Torque \*RPMs )/5252 gives horsepower. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [July 23, 2002, 8:06pm UTC](https://boards.straightdope.com/t/why-do-liters-equate-to-engine-power/120378/19 "2002-07-23T20:06:13Z")
\>\> I always found that 1 Liter=61.4 cubic inches as a good conversion factor Define “good”. Good for what? 1 l = 1000 / 2.54^3 (exactly) ~ 61.024 approx. So we have a thread where quite a few people cannot convert US to metric and back and some do not even know that cubic inches and liters are both units of volume. Then we have a thread asking if the US educational system is really so bad. And another thread congratulating ourselves as members of this board for fighting ignorance so hard and being so intelligent. An interesting combination. ---
**Author:** ![MilTan](https://avatars.discourse-cdn.com/v4/letter/m/71e660/32.png) [@MilTan](https://boards.straightdope.com/u/MilTan)\ **Post date:** [July 23, 2002, 9:25pm UTC](https://boards.straightdope.com/t/why-do-liters-equate-to-engine-power/120378/20 "2002-07-23T21:25:59Z")
**Enola** (and anyone else): Where does that 5252 number come from? And furthermore, shouldn’t that equation mean that maximum horsepower occurs at the same RPM as max torque? But I don’t think that’s true for my car. [Next page](https://boards.straightdope.com/t/why-do-liters-equate-to-engine-power/120378.md?page=2)