Smaller Engine/Displacement = Fuel efficient?

[lesnar]

Is it more fuel efficient if a car has a smaller fuel displacement or smaller engine on a SUV/minivan?

I've read/heard that smaller engine does not mean more fuel efficient because the engine is always running at it's threshold whereas a larger/more horsepower engine on the same car won't have to work as hard.

Your inputs please.

[new_vr]

Is it more fuel efficient if a car has a smaller fuel displacement or smaller engine on a SUV/minivan?

I've read/heard that smaller engine does not mean more fuel efficient because the engine is always running at it's threshold whereas a larger/more horsepower engine on the same car won't have to work as hard.

Your inputs please.

It isn't necessarily more efficient. it might have to work harder to make the car move, which can lead to bad fuel economy. Also, final gear ratios can make a difference too

[sexpuppet6000]

very intersting question.

i think if you are looking to purchase a car you shouldn't concern yourself with engine displacement in terms of how efficient the car is. the manufacture probaly engineered it to its best.

it also depends on if you are driving on the highway or not.

[ES_Revenge]

Not necessarily, there are a lot of factors... That's why there's standardised fuel economy ratings from the government, for all consumer vehicles. They aren't always that accurate either but it's good to use as a general guide.

[googoo]

Yeah, displacement doesn't tell the whole story, just look at the 1.3 litre engine in the Mazda RX8, it's a gas hog.

Brent

[plucky duck]

I wouldn't say so either. Initially I thought that would be the case, going down to a 2.2L 4Cyclinder Honda from an V6 Intrigue. City and highway driving it's pretty comparable. The Intrigue is heavy, but has a decent engine to pull its weight without much trouble. The Prelude, on the other hand, is also quite heavy at 3100lbs for such a small car, yet the inline4 struggles quite a bit in the city (lack of torque) and has to revv pretty high even at highway cruise speeds (100-120km/h). Wish the Prelude had a 6th gear.

Driving like a grandma is no fun. But so is throwing money out senselessly for gas. With the Intrigue I can cruise around the city from light to light effortlessly. With the Prelude, unless I'm on it I'm not getting anywhere and most likely holding up traffic.

Depends on the use of the vehicle, size, and weight.

[ES_Revenge]

I wouldn't say so either. Initially I thought that would be the case, going down to a 2.2L 4Cyclinder Honda from an V6 Intrigue. City and highway driving it's pretty comparable. The Intrigue is heavy, but has a decent engine to pull its weight without much trouble. The Prelude, on the other hand, is also quite heavy at 3100lbs for such a small car, yet the inline4 struggles quite a bit in the city (lack of torque) and has to revv pretty high even at highway cruise speeds (100-120km/h). Wish the Prelude had a 6th gear.

Driving like a grandma is no fun. But so is throwing money out senselessly for gas. With the Intrigue I can cruise around the city from light to light effortlessly. With the Prelude, unless I'm on it I'm not getting anywhere and most likely holding up traffic.

Perhaps going OT for a second... This is a great explanation, first hand, of why torqueless wonder motors aren't so hot for daily driving. Yet many people, particularly all the teenagers/young ppl, don't even begin to understand this for some reason (well I guess there is a reason, many also don't understand why they can't go ludicrous speed on public roads either, lol).

The 2.2L in the Prelude isn't even that bad. When it's taken to rather ridiculous extremes like the S2000 and latest Civic Si, it's that much worse. It's amazing when you try to tell people how these cars are largely useless in terms of their lofty hp numbers in real-world driving, it's like they don't even hear you. Like all they see is numbers "200hp" and "40mpg", nevermind to see anything even near that 200hp the fuel economy drops like a brick because you're running the engine above where most cars have redlined, LOL.

But at least it's nice to see someone make a real world comment about this, because then maybe all the boy-racers with their aspirations of superhigh horsepower per litre and crazy fuel economy will realise you don't really get both of these at the same time.

Engines that make power from sheer RPM are great for racing but you don't race on the road everyday (in fact you shouldn't be "racing" at all--it's illegal). However many buyers of these cars completely disregard that and again just see lofty numbers the word Honda and think it's God's gift to the automotive world :rolleyes: It's great that these engines accomplish what they do (the "wonder" in torqueless wonder, lol) but they are largely useless and rather silly IMO, in the real world.

There's definitely something to be said for low-end torque, but unfortunately a lot of people never listen to it :(

[notanexpert]

From a pure engineering standpoint, an engine works most efficiently at wide open throttle (pedal to the metal...). That is, it produces the most power for a given amount of fuel at wide open throttle.
So, a 100hp engine will be consuming less fuel at wide open throttle than a 400hp engine working at 1/4 throttle and producing 100hp as well.
But all of this theory gets thrown out the window once the engine is installed in a car, because you're always comparing apples to oranges: different weights, different axle ratios, different transmission ratios/number of gears, different driving styles that suit each car, etc, etc.

[KawaiiTentacleBeast]

All I can say is that I wish Mazda still made 13B-powered pickup trucks.

http://www.mazdarepu.com/Gallery/uploads/rollbaredrepu2.jpg


They should make a new one with sequential twin turbos too, for maximum insanity.

[new_vr]

From a pure engineering standpoint, an engine works most efficiently at wide open throttle (pedal to the metal...). That is, it produces the most power for a given amount of fuel at wide open throttle.
So, a 100hp engine will be consuming less fuel at wide open throttle than a 400hp engine working at 1/4 throttle and producing 100hp as well.
But all of this theory gets thrown out the window once the engine is installed in a car, because you're always comparing apples to oranges: different weights, different axle ratios, different transmission ratios/number of gears, different driving styles that suit each car, etc, etc.
Are you sure about that? pedal to the medal, my car will hit redline. My hp curve actually starts going down before redline.

[woodstock827]

Are you sure about that? pedal to the medal, my car will hit redline. My hp curve actually starts going down before redline.

That's because friction and inertia kicks in and there may not be enough air to support the fuel.

[ES_Revenge]

From a pure engineering standpoint, an engine works most efficiently at wide open throttle (pedal to the metal...). That is, it produces the most power for a given amount of fuel at wide open throttle.
True, however, making power with atmospheric manifold pressure (assuming no forced induction) is not necessarily going to save you fuel in absolute terms. Without a CVT it's tough to get a ratio that's going to give you the gearing to make an engine consume as little fuel as you'd want with a large throttle opening. In fact even CVTs in cars are limited in their range of effective ratio, so it's doubful you'll be cruising with the throttle wide open even in those cars, right?

When most people think of fuel efficiency they really just mean economy and accounting for gearing and how that power gets to the road, a wide open throttle is not really going to get you the best fuel economy (in fact it's probably going to get you the worst, lol).


So, a 100hp engine will be consuming less fuel at wide open throttle than a 400hp engine working at 1/4 throttle and producing 100hp as well.
All things being equal of course. If the engines are of completely different design or have different technologies in them, it'll be tough to say that. In fact it would really be tough to make two engines similar enough but making as different amounts of power as that.

Also the engine at 1/4 throttle has nothing to do with quartering it's maximum horsepower. Horsepower developed is all about torque and RPM. If you could have gearing and engine torque at a certain RPM, such that you could get a 1/4 open throttle to give 100hp, at the RPM same given at that 1/4 open throttle, then you could say this.

You'll see a slightly chicken/egg type syndrome there with the RPM because the engine also creates torque dependent on it's RPM as a matter of output; but as a matter of calculation you need to have torque and RPM to find out horsepower. So when talking about stuff like this it is easier to leave horsepower (which is merely calculated) out of the equation (pun intended I guess haha) and just refer to engine torque which is what the engine actually produces.

Throttle opening is largely irrelevant to output power. You can open the throttle fully on your car at any point but you will not have the full engine power until the engine reaches the RPM point where it would be ouputting maximum power. Similarly you could have a very small throttle opening and gearing that has the engine running at the RPM where maximum power is created.

The throttle opening (and what you're after here) is significant in terms of volumetric efficiency, sure; but again I think this whole discussion is a little outside the scope of just trying to find a car with good fuel economy. :D

But all of this theory gets thrown out the window once the engine is installed in a car, because you're always comparing apples to oranges: different weights, different axle ratios, different transmission ratios/number of gears, different driving styles that suit each car, etc, etc.
Yep.

This is why I said above, use the government ratings for goodness sakes! That's what they are there for!

[ES_Revenge]

Are you sure about that? pedal to the medal, my car will hit redline. My hp curve actually starts going down before redline.

Two things... First we're not really talking about peak horsepower in absolute terms, we're talking about power delivered for fuel consumed. So the hp curve "going down" isn't important. Second, your car will hit redline because of gearing. If you could use a gear ratio such that the car would not hit redline (or actually not even necessarily be at it's power peak at all), with the throttle wide open, it will have 100% volumetric efficiency which is really what he was getting at I believe. (Again this is assuming no forced induction as cars with turbo or superchargers acheive >100% volumetric efficiency.)

[new_vr]

Two things... First we're not really talking about peak horsepower in absolute terms, we're talking about power delivered for fuel consumed. So the hp curve "going down" isn't important. Second, your car will hit redline because of gearing. If you could use a gear ratio such that the car would not hit redline (or actually not even necessarily be at it's power peak at all), with the throttle wide open, it will have 100% volumetric efficiency which is really what he was getting at I believe. (Again this is assuming no forced induction as cars with turbo or superchargers acheive >100% volumetric efficiency.)
I do think it is still significant that the hp curve goes down, because this means that more fuel doesn't necessarily mean more power.

[c0ppertop]

Only one old car qualifies for Utah's free parking (ulta high MPG cars).

And that's a 3 cylinder Metro (XFI). So, less displacement, less pistons, less weight, all lead to high fuel efficiency. I think it gets 48MPG.

That's 1994 technology/know how. In the following years, cars have gotten fatter, and less fuel efficient, why? Because the CONSUMER demands big fat SUV's. Sorry a Yaris doesn't cut it for me (or a 'Smart' car).

[notanexpert]

Two things... First we're not really talking about peak horsepower in absolute terms, we're talking about power delivered for fuel consumed. So the hp curve "going down" isn't important. Second, your car will hit redline because of gearing. If you could use a gear ratio such that the car would not hit redline (or actually not even necessarily be at it's power peak at all), with the throttle wide open, it will have 100% volumetric efficiency which is really what he was getting at I believe. (Again this is assuming no forced induction as cars with turbo or superchargers acheive >100% volumetric efficiency.)

Exactly. This is what I'm saying.
Therefore, the most efficient car, in theory, for that hypothetical trip to Montreal, would be something that only had enough power to get to 120km/h, if that is how fast you wanted to travel. So you'd floor it at your house in TO and only let go of the gas when you arrived in Montreal. This way, the engine would be running at 100% volumetric efficiency (assuming natural aspiration), and this would yield better fuel efficiency than any bigger engine that you'd not have to be flooring the entire way, ALL OTHER THINGS BEING EQUAL.

[notanexpert]

I do think it is still significant that the hp curve goes down, because this means that more fuel doesn't necessarily mean more power.

If you're over-reving an engine to the point that it is loosing power, it is also using less fuel. An engine that produces maximum power at 6000 rpm, will use less fuel at 7000 rpm than at 6000rpm. This is because at 7000rpm the cylinders can not get filled with the air/fuel mixture as well as they can at 6000rpm.

[anycee]

Perhaps going OT for a second... This is a great explanation, first hand, of why torqueless wonder motors aren't so hot for daily driving. Yet many people, particularly all the teenagers/young ppl, don't even begin to understand this for some reason (well I guess there is a reason, many also don't understand why they can't go ludicrous speed on public roads either, lol).

The 2.2L in the Prelude isn't even that bad. When it's taken to rather ridiculous extremes like the S2000 and latest Civic Si, it's that much worse. It's amazing when you try to tell people how these cars are largely useless in terms of their lofty hp numbers in real-world driving, it's like they don't even hear you. Like all they see is numbers "200hp" and "40mpg", nevermind to see anything even near that 200hp the fuel economy drops like a brick because you're running the engine above where most cars have redlined, LOL.


Really, do you buy an S2000 for fuel economy?
Personally, I like high reving engines: if I need power, I can gear down and get it. If you run the car in the 3-4k range, you get good power and good economy, and if you need the real power it is only a downshift away.

[ES_Revenge]

I do think it is still significant that the hp curve goes down, because this means that more fuel doesn't necessarily mean more power.
Yeah but that's still irrelevant. We're not talking about more fuel means more power or not, we're talking about the most power for the fuel burned, or the most fuel efficiency for the engine.

You're right that more fuel doesn't necessarily mean more power but it has little to do with what was being discussed ;)

Really, do you buy an S2000 for fuel economy?
Personally, I like high reving engines: if I need power, I can gear down and get it. If you run the car in the 3-4k range, you get good power and good economy, and if you need the real power it is only a downshift away.
:rolleyes:

You completely missed the point (surprise, surprise). And no I wouldn't buy an S2000 for fuel economy, well I wouldn't buy one to begin with, and I wouldn't really buy any car for fuel economy, lol. But you will indeed see people talking about the fuel economy of these cars, moreso the Civic, but they still do with the S2000.

But again you still completely missed the point, which is perhaps ironic. I'm not going to go over it again because I'd just be repeating myself and then you'd just be completely talking about something else again, and there's no point in crapping up this thread.

PS: Oh and you do not get "good power" out of the Honda 2.xL 2xxhp engines in these cars at 3k RPM. Well not unless you consider Toyota Tercel-like power as "good" LOL. Because yes, a Tercel will be roughly even with them, in a 0-60 run, if you don't go over ~7k.

[googoo]

"Perhaps going OT for a second... This is a great explanation, first hand, of why torqueless wonder motors aren't so hot for daily driving."

REALLY LOL:) I'm sure it's nice to get to the next stoplight faster than I do in my Civic, but I never have a hard time keeping up to traffic on the roads. So the argument that high torque #s are better makes more sense when the load is extreme(car is full) or the terrain calls for it. The argument that you have to rev the engine up is mute, anybody buying these types of cars knows what they are getting Into. Ontario it's pretty flat, only if I was heading up Hamilton Hill would I wish for more torque. Now don't get me wrong, going up and down the Cape Breton Trail I wished for some more torque, but getting 48MPG at 110KPH on the highway made me much happier than revving my engine to 4000RPM LOL

Brent LOL

[new_vr]

You're right that more fuel doesn't necessarily mean more power but it has little to do with what was being discussed ;)

I thought the argument was that engines are most efficient under WOT, and my point is that isn't necessarily the case

[notanexpert]

I thought the argument was that engines are most efficient under WOT, and my point is that isn't necessarily the case

But it IS the case. Just because an engine can't "breathe" as well at rpm that is higher than its maximum HP rpm, does NOT mean that its wasting fuel. If it can't "breathe" any more, its not using any more fuel either, as the fuel injection computer keeps the air/fuel ratio constant.

[new_vr]

But it IS the case. Just because an engine can't "breathe" as well at rpm that is higher than its maximum HP rpm, does NOT mean that its wasting fuel. If it can't "breathe" any more, its not using any more fuel either, as the fuel injection computer keeps the air/fuel ratio constant.

Ok...that's the part I was missing out on..I wasn't thinking the computer was smart enough to quit sending fuel to the system

[corrupt123]

BMW is pretty good at warping the power/fuel consumption numbers. I don't know the specifics of how it works, but they manipulate a lot of things. Hell, the massive 750i produces 360 horse (4.8l) and gets 17/25 mpg.

[lesnar]

ANYWAYS, amazing how fast the responses are...


So should i get a Mazda Tribute I4 or V6?

Remeber, It's the same car. i'm not comparing apples and oranges here.

which is more efficient for daily driving.

[notanexpert]

ANYWAYS, amazing how fast the responses are...


So should i get a Mazda Tribute I4 or V6?

Remeber, It's the same car. i'm not comparing apples and oranges here.

which is more efficient for daily driving.

Still a little apples and oranges because they don't weigh the same, they don't have the same transmission ratios and they probably don't have the same final drive ratios...
But anyway, I'm confident that in "normal" day to day driving, you will save at least 10% on fuel with the 4-cylinder versus the V6.

[notanexpert]

BMW is pretty good at warping the power/fuel consumption numbers. I don't know the specifics of how it works, but they manipulate a lot of things. Hell, the massive 750i produces 360 horse (4.8l) and gets 17/25 mpg.

Valvetronic! They don't have a throttle closing off the intake, they work at near perfect volumetric efficiency because they use the variable valve lift system to limit the amount of air/fuel mixture drawn into the cylinder. Its a much more efficient and complex way of feeding the engine but results in better fuel efficiency.

[ES_Revenge]

"REALLY LOL:) I'm sure it's nice to get to the next stoplight faster than I do in my Civic, but I never have a hard time keeping up to traffic on the roads. So the argument that high torque #s are better makes more sense when the load is extreme(car is full) or the terrain calls for it.
Nope, it makes sense no matter how you slice it. No need for drama, just tap the throttle and the car goes. It's better than craziness like double-clutching and huge throttle openings just to get the car to move at all, lol. Now not all cars are this bad but some are just that extreme--the ones I mentioned are quite gutless below RPM levels that are not beyond the redline in the majority of cars.

"The argument that you have to rev the engine up is mute,
Mute? :confused: Did you mean moot?

anybody buying these types of cars knows what they are getting Into.
False assumption.

Ontario it's pretty flat, only if I was heading up Hamilton Hill would I wish for more torque.
"More torque" is certainly not just for climbing hills. Again the point is lost here unfortunately :(

Now don't get me wrong, going up and down the Cape Breton Trail I wished for some more torque, but getting 48MPG at 110KPH on the highway made me much happier than revving my engine to 4000RPM LOL
Well, as long as you're happy :)

[googoo]

False assumption?? hmm you'd figure most people would figure this out on a test drive.

OH, yes moot sorry.

Just allow the thought that you are wrong, just once LOL

Brent
This LOL thing is just really silly, almost as bad as IMO, but it would be nice to see that it is your opinion now and then.

[anycee]

Yeah but that's still irrelevant. We're not talking about more fuel means more power or not, we're talking about the most power for the fuel burned, or the most fuel efficiency for the engine.

You're right that more fuel doesn't necessarily mean more power but it has little to do with what was being discussed ;)


:rolleyes:

You completely missed the point (surprise, surprise). And no I wouldn't buy an S2000 for fuel economy, well I wouldn't buy one to begin with, and I wouldn't really buy any car for fuel economy, lol. But you will indeed see people talking about the fuel economy of these cars, moreso the Civic, but they still do with the S2000.

But again you still completely missed the point, which is perhaps ironic. I'm not going to go over it again because I'd just be repeating myself and then you'd just be completely talking about something else again, and there's no point in crapping up this thread.

PS: Oh and you do not get "good power" out of the Honda 2.xL 2xxhp engines in these cars at 3k RPM. Well not unless you consider Toyota Tercel-like power as "good" LOL. Because yes, a Tercel will be roughly even with them, in a 0-60 run, if you don't go over ~7k.

The point was that the hp figure was misleading as it would never be reached under daily driving, and that that made the fuel economy figure especially misleading?

My point is that you don't need constant access to 200 hp, or even 150 hp for a 2801 lbs car you are using as a daily driver. If you think you need to be above 4K rpm at WOT around town, you must be living in a different town than I am. If you are on the highway and need to pass, you can downshift. So it doesn't matter that the car doesn't produce enough torque at low rpm to make your passenger **** themselves: you don't need that much power on the street. If you are doing 0-60s (well, 0-40s) at every stoplight, you are a reckless driver.

EDIT: I may be totally off here, this is just coming from my experiance of accelerating faster than almost all cars at stoplights by shifting at 4k with WOT in a far cheaper car than an s2000. The only people who take off faster seem to be crazed soccer moms who floor minivans and people who think I am racing them.

[plucky duck]

With good low end torque a vehicle can move from a complete stop pretty effortlessly. And that's the point of having that torque at your disposal is that one doesn't necessarily need to "downshift" to "move". I'd really rather not have to revv like a mofo just to get my car going and hear the engine scream like a little girl :lol: Under 4k the car is hardly responsive.

Too many people look at cars purely by their hp ratings, which in the real world don't really mean much at all, especially city driving. I care more about weight, gearing, and displacement.

Many people eye the H22 and I wondered why. Because it isn't particularly torquey (compared to Civic, Vigor, Legends and Prelude engines of that generation) or powerful. But apparently its popular because paired with an older lightweight Civic shell it really flies. That's part of the puzzel. An engine, paired with the right shell and right tranny and gearing, can really either shine or appear to perform lacklustre. Perhaps a good example would be slapping a V6 in a pickup truck. Generally seen as a bad pairing.

Meh, maybe I'm just growing old and want some "real" power. V8-V12 here I come baby!! :lol:

[gordholio]

Generally speaking, a smaller engine means better gas mileage, but of course there are exceptions. The weight of the car is a big factor too.
My car has only 92 hp (1.5 liter), but weighs only about a metric ton and gets 44 mpg.