Low Power Output and High Displacement, a big debate.

[Grayfox]

How'd you work that one out? The numbers you're looking at are kilometres... In which case, 100km/h (60 ish mph) is quite obviously going to be more economical than 50km/h (30 ish mph) because at 30mph the Vette is well out of the usable torque band and it ends up labouring in 5th gear (fuel efficiency would more than likely improve at 30mph by dropping another gear, as BrutherSuperior suggested earlier), whilst doing half the speed it would be doing at 60mph so it's not covering as much ground for all that fuel being used either.

At 100mph you'll probably be looking at 15mpg or less, judging by the way that graph is heading. At 50mph it's getting over 30mpg, which isn't that bad. Over twice the MPG that 100mph would likely provide, in fact. Almost certainly significantly more than twice that MPG, since you'd soon start getting into the rapidly increasing spiral of engine friction, as well as exponential aero drag.

You get 28.7MPG @ 50MPH and 30MPG @ 100MPH.

 

[homeforsummer]

You get 28.7MPG @ 50MPH and 30MPG @ 100MPH.

Again: you're reading the figures for kilometres per hour, not miles per hour.

I know it must be confusing reading two lines of text one on top of the other, but seriously two of you have failed to notice it?

 

[Tornado]

I was going to make a pithy comment about "if you are still getting 26MPG at 120 MPH, why would you not go that fast" until I stopped and reread it.

 

[Mr. CoolFiat]

Some more questions since I've figured you guys are like all Yodas of cars or something:
1. Have tires gotten better since the 80's? If so, in which way?
2. Has safety, and all the electronics + all the safety equipment needed, influenced fuel economy?
3. Would a 3 liter V6 sedan making 145 horsepower, complete with the 4 speed auto trannys of the 80's be better off due to the flexibility of the engine than a 1.4 liter Direct Fuel Injection 3 cylinder with turbocharging and a 6 speed tranny with super long overdrive gears, and which looks like a cube?
Since cars have gotten smaller, did that make them more fuel efficient in some ways? If you need to rev the engine just to make at least 60 horses, how is that fuel efficient???

 

[nick09]

My 2003 Malibu car seems to make the best use of it's gas in the 68-69 mph sweet spot. I've finished driving today with 3/4th of the 14.1 Gallon tank leftover and I've driven 117 miles. 1/4th of my tank is about 3.525 gallons and my calculations says my car has been doing 33MPG. I've read that this has been done with my type of car though that is only highway miles. Once I combine City driving it should come down to 24-26MPG(I normally do this every week with Cruse control and running some AC).

Personally I think it's making the best use of the engine in any given situation will help you get that extra MPG. They do have those low friction tires but I think you will lose the ability to grip compared to normal tires in some situations and that those tires would wear down faster. I might of gotten that 33MPG since I've readjusted the tire's PSI(40's in the front and 35's in the rear) since I saw my right front tire bending more than usual(it did have less PSI in it than the left tire). Though there is a lot more variables I've probability have not touched yet and don't have enough experience with to share any advice for.

 

[Eric.]

Some more questions since I've figured you guys are like all Yodas of cars or something:
1. Have tires gotten better since the 80's? If so, in which way?
2. Has safety, and all the electronics + all the safety equipment needed, influenced fuel economy?
3. Would a 3 liter V6 sedan making 145 horsepower, complete with the 4 speed auto trannys of the 80's be better off due to the flexibility of the engine than a 1.4 liter Direct Fuel Injection 3 cylinder with turbocharging and a 6 speed tranny with super long overdrive gears, and which looks like a cube?
Since cars have gotten smaller, did that make them more fuel efficient in some ways? If you need to rev the engine just to make at least 60 horses, how is that fuel efficient???

1) Yes, all of them 2)Yes, if a car is heavier due to that equipment, it will require more power to move around. 3)Depends how the turbo car is tuned, it may make a flatter torque curve and be better off all around (assuming it makes equivalent power as the V6), and it will be more flexible by having more gear choices.

 

[homeforsummer]

1. Have tires gotten better since the 80's? If so, in which way?
2. Has safety, and all the electronics + all the safety equipment needed, influenced fuel economy?
3. Would a 3 liter V6 sedan making 145 horsepower, complete with the 4 speed auto trannys of the 80's be better off due to the flexibility of the engine than a 1.4 liter Direct Fuel Injection 3 cylinder with turbocharging and a 6 speed tranny with super long overdrive gears, and which looks like a cube?
Since cars have gotten smaller, did that make them more fuel efficient in some ways? If you need to rev the engine just to make at least 60 horses, how is that fuel efficient???

As above:

1) Tyres are improving all the time. Generally today's tyres have more grip, longer life, better wet weather characteristics, less noise and lower rolling resistance than tyres of even five and ten years ago, let alone 20 or 30 years.

2) All the extra weight of safety tech and electronics has meant a car of equivalent spec would have to work harder than a car from back in the day, but at the same time the pace of technology has still generally outpaced the extra weight that cars have gained - so today's cars generally perform better and give better economy despite the extra weight.

3) Hard to say. Generally the big engine with the low horsepower and low-tech transmission would be incredibly inefficient in most measurable ways than the modern, small, turbocharged unit. It might have better torque but with a 3-speed slushbox it's not best placed to utilise it, so the small engine may still offer more usable characteristics.

Cars getting smaller doesn't automatically mean they have to work harder - it's the engine that's responsible for that. A small car with a small engine won't necessarily have to work harder than a medium sized car with a medium sized engine (for sake of argument), but it'll take less coaxing than a medium car with a small engine - or more than a medium car with a large engine.

There's a law of diminishing returns. Below a certain point a small engine in a small car will need too much thrashing to be truly efficient (Japanese Kei cars are a case in point - the 660cc engines aren't actually that efficient as a rule), and a larger engine in a larger car will just be using fuel that it doesn't necessarily need to move it along the road.

 

[Mr. CoolFiat]

As above:

1) Tyres are improving all the time. Generally today's tyres have more grip, longer life, better wet weather characteristics, less noise and lower rolling resistance than tyres of even five and ten years ago, let alone 20 or 30 years.

2) All the extra weight of safety tech and electronics has meant a car of equivalent spec would have to work harder than a car from back in the day, but at the same time the pace of technology has still generally outpaced the extra weight that cars have gained - so today's cars generally perform better and give better economy despite the extra weight.

3) Hard to say. Generally the big engine with the low horsepower and low-tech transmission would be incredibly inefficient in most measurable ways than the modern, small, turbocharged unit. It might have better torque but with a 3-speed slushbox it's not best placed to utilise it, so the small engine may still offer more usable characteristics.

Cars getting smaller doesn't automatically mean they have to work harder - it's the engine that's responsible for that. A small car with a small engine won't necessarily have to work harder than a medium sized car with a medium sized engine (for sake of argument), but it'll take less coaxing than a medium car with a small engine - or more than a medium car with a large engine.

There's a law of diminishing returns. Below a certain point a small engine in a small car will need too much thrashing to be truly efficient (Japanese Kei cars are a case in point - the 660cc engines aren't actually that efficient as a rule), and a larger engine in a larger car will just be using fuel that it doesn't necessarily need to move it along the road.

Holy Toblerone!! You know a lot... and thanks Eric for your input too!
I will be asking more questions when they pop up in my head.... until then, cheers!

 

[CSLACR]

How'd you work that one out? The numbers you're looking at are kilometres... In which case, 100km/h (60 ish mph) is quite obviously going to be more economical than 50km/h (30 ish mph) because at 30mph the Vette is well out of the usable torque band and it ends up labouring in 5th gear (fuel efficiency would more than likely improve at 30mph by dropping another gear, as BrutherSuperior suggested earlier), whilst doing half the speed it would be doing at 60mph so it's not covering as much ground for all that fuel being used either.

At 100mph you'll probably be looking at 15mpg or less, judging by the way that graph is heading. At 50mph it's getting over 30mpg, which isn't that bad. Over twice the MPG that 100mph would likely provide, in fact. Almost certainly significantly more than twice that MPG, since you'd soon start getting into the rapidly increasing spiral of engine friction, as well as exponential aero drag.

I see.
But what makes you think they didn't use 4th gear for 30mph?

So now how incredibly slow must we drive to maximize efficiency in a small, light box car? Apparently my estimates of 40mph were still to high.

Also, if EPA stickers looked like that, well, the slowest traffic dominates the roadway speed, oh boy...
Interesting thing to add, I've never achieved better mileage in third gear than fourth, which I can't use until 45mph minimum.

 

[Bottoz]

...
3. Would a 3 liter V6 sedan making 145 horsepower, complete with the 4 speed auto trannys of the 80's be better off due to the flexibility of the engine than a 1.4 liter Direct Fuel Injection 3 cylinder with turbocharging and a 6 speed tranny with super long overdrive gears, and which looks like a cube?
Since cars have gotten smaller, did that make them more fuel efficient in some ways? If you need to rev the engine just to make at least 60 horses, how is that fuel efficient???

If I had to choose, I'd take the 1.4 DI Turbo.

Just throwing it out here... but here is a dyno of a 1.6 DI Turbo. Stock.

Lots of torque down low, makes it much easier to drive than your typical 4-banger. Good on gas too. 33mpg in town.

 

[niky]

By the way, here's my concept for the sticker...



More than easy enough to understand, even if you don't read the numbers. Would make the EPA's job of trying to convince people to save gas much easier without actually making consumers feel like they're being forced to...

Some more questions -snip

1. Tires are better. There are "fuel saving" tires nowadays. These are generally harder and longer lasting. They don't affect lateral grip much, but I've never been much impressed by braking distances with these tires. Obviously, they're designed for less rolling resistance when moving in a straight line, so when you're braking in a straight line...

2. Airbags and ABS/EBD/DSC controllers don't weigh that much by themselves. You could counter that weight gain simply by changing from a full-sized spare to a space saver. What really hurts is that customers want more space. Governments want more safety. Manufacturers want lower costs. Thus the "body-in-white", the bare steel bones of the car has gotten heavier and heavier over the years. A fully stripped out Civic from twenty years ago weighs around 200 pounds less than a fully stripped out Honda Fit with the same engine... and that's with more sophisticated double-wishbones underneath compared to the simpler McPherson and torsion-beam system in the Fit, not to mention the weight-saving L-series engine in the newer car.

And yet, that same Honda Fit is much safer than the Civic... fully able to withstand a frontal impact with a twenty year old Accord, whereas the older car would crumple like paper... and the Fit just happens to be a whole lot more spacious, while still being pretty handy to drive.

3. As said, depends a lot on the particular engines and the actual gear ratios.

To note: Kei cars would be rubbish in America. At US highway cruising speeds, they'd be doing "merely" around 40 mpg. But driven in their environment at typical Japanese rural cruising speeds, they can get much, much more. At a 45 mph cruise, I've seen some get well over 70 mpg. At the link I provide, ecomodder, there are enthusiasts with the Geo Metro who've gotten 80+ by swapping out to longer gears and fuel saving cams.

----

The last question neatly puts us back on topic, huh?

Big engines with low output are actually much like small turbos in that they produce more torque than you'd expect given their peak power output. This is great for economy as it gets you up to speed quicker, and allows you to maintain cruise in gear at ridiculously low rpms (as the Corvette graph shows... it allows a 500 hp engine to almost hit 40 mpg! Cruising at idle!).

The problem is a big engine will still drink a lot at idle, unless you use cylinder deactivation or start-stop systems. If you're starting with smaller engines, you don't have to muck around as much to lower consumption at idle or low loads... but you do have the problem of extra heat (more power out of smaller package = more heat)... which is why direct injection is important on new downsized turbocharged engines... otherwise you'd be wasting gas cooling them off, running pig-rich like old-school Evos did.

Big lazy engines still have their place in applications which don't require much changes in speed (shipping, locomotives), but downsizing is the future of motoring.

 

[CSLACR]

By the way, here's my concept for the sticker...



More than easy enough to understand, even if you don't read the numbers. Would make the EPA's job of trying to convince people to save gas much easier without actually making consumers feel like they're being forced to.

Seems effective, though I should say I think most Americans problem is city driving, where they either race off lights only to stop at the next, or on the flip side, they drive entirely to slow, never get into a more efficient gear/speed range, and the lights go full cycle and they still get stuck at the next light.
And then there's the traffic lights, most of which around me require nothing to get through, you simply will catch 75% of all red lights regardless, and not a single one of them ever goes into "blink mode", which means late at night, I often find myself stopping and pissing fuel away only to watch (eventually) someone else come up, and catch the light as mine turns green, and the cycle continues...
I think with a better traffic light system (Blinking 11pm - 6AM, and better timing in the daytime) the people of the area could save a massive unknown quantity of fuel each year.
Oh did I mention, being in the Appalachian mountains means stopping halfway up large hills half the time?

 

[niky]

City is problematic... as that's harder to compress into a read-on-sight infographic.

Mountains are something else entirely. They teach us to not maintain speed going up a grade, but obviously you can't drop speed for several miles going uphill!

One interesting technique learned from SCC's Ultimate Street Car Challenge.... accelerate going downhill... then use the momentum built up to coast up the next rise. The contestant who did that managed to top 40 mpg in the hills with a highly-modified turbocharged car.

 

[CSLACR]

City is problematic... as that's harder to compress into a read-on-sight infographic.

Mountains are something else entirely. They teach us to not maintain speed going up a grade, but obviously you can't drop speed for several miles going uphill!

One interesting technique learned from SCC's Ultimate Street Car Challenge.... accelerate going downhill... then use the momentum built up to coast up the next rise. The contestant who did that managed to top 40 mpg in the hills with a highly-modified turbocharged car.

You wouldn't mean an MR2 now would you? I remember that if that's the one you speak of.
Generally I don't accelerate downhill, due to speed limits, and most of the time, enough speed is gained by coasting, just making sure you're back on the throttle before you flatten out to keep momentum for the uphill.
On some hills you can just turn the key back one click.

 

[homeforsummer]

I see.
But what makes you think they didn't use 4th gear for 30mph?

The fact that the graph also says which gear they used 5th, for 30mph, 6th for the others. Again, I went over this!:

How'd you work that one out? The numbers you're looking at are kilometres... In which case, 100km/h (60 ish mph) is quite obviously going to be more economical than 50km/h (30 ish mph) because at 30mph the Vette is well out of the usable torque band and it ends up labouring in 5th gear (fuel efficiency would more than likely improve at 30mph by dropping another gear, as BrutherSuperior suggested earlier), whilst doing half the speed it would be doing at 60mph so it's not covering as much ground for all that fuel being used either.

At 100mph you'll probably be looking at 15mpg or less, judging by the way that graph is heading. At 50mph it's getting over 30mpg, which isn't that bad. Over twice the MPG that 100mph would likely provide, in fact. Almost certainly significantly more than twice that MPG, since you'd soon start getting into the rapidly increasing spiral of engine friction, as well as exponential aero drag.

So now how incredibly slow must we drive to maximize efficiency in a small, light box car? Apparently my estimates of 40mph were still to high.

40mph is probably about right.

Really, the best efficiency will probably be no less than 40mph in most cars, because above that wind resistance increases much more rapidly, and all but very tall-geared cars should be able to manage light-throttle cruising at around 40mph in top gear (again - not accelerating, where changing down may be more efficient - but most cars will have enough power in top gear to keep the car rolling at a constant 40mph on a very, very light throttle opening).

Interesting thing to add, I've never achieved better mileage in third gear than fourth, which I can't use until 45mph minimum.

How many gears does your car have? The most efficient spot will be in top gear, with revs low enough to use as little fuel as possible without having to constantly downchange for traffic conditions.

Edit:

Niky - love the graph. It's brilliant, simple to understand. I could envisage a similar version for electric cars, giving their estimated range at particular speeds - say, 100 miles in city traffic, 95 miles at 50mph, 90 at 60mph, 70 at 70mph etc.

Seems effective, though I should say I think most Americans problem is city driving, where they either race off lights only to stop at the next, or on the flip side, they drive entirely to slow, never get into a more efficient gear/speed range, and the lights go full cycle and they still get stuck at the next light.

Unfortunately, fuel economy estimations have never been able to account for the more moronic reaches of our society...

 

[CSLACR]

The fact that the graph also says which gear they used 5th, for 30mph, 6th for the others. Again, I went over this!:

Missed it It won't happen again sir.

40mph is probably about right.

Really, the best efficiency will probably be no less than 40mph in most cars, because above that wind resistance increases much more rapidly, and all but very tall-geared cars should be able to manage light-throttle cruising at around 40mph in top gear (again - not accelerating, where changing down may be more efficient - but most cars will have enough power in top gear to keep the car rolling at a constant 40mph on a very, very light throttle opening).

It seems to me like that's to arbitrary with little or no regard for weight.
Also keep in mind, these numbers are (apparently) for flat roads, while I know of and have driven places where flat roads dominate, it's certainly not an "everywhere" thing. The hillier it gets, the more momentum wins.

How many gears does your car have? The most efficient spot will be in top gear, with revs low enough to use as little fuel as possible without having to constantly downchange for traffic conditions.

4, but from other posts it's been said with different or quicker gearing some cars can manage better mileage at lower speeds, whereas my car has a hard time pulling at the "beginning" of third and fourth (roughly 1400rpm), at any speed third does not manage the mileage fourth does. But that may be due to my hilly conditions, hard to say.

Unfortunately, fuel economy estimations have never been able to account for the more moronic reaches of our society...

If more moronic means "majority" I agree.
But they could have "gentle" "average" and "aggressive" readings, since city driving is where people and cars suffer the worst mileage, it seems more important to me to focus on improving peoples city driving habits rather than rural and highway.
Of course some cars are just flat out screwed by their transmissions (mine) in the city, where even on flat roads 2000 rpm is unavoidable until it reaches third gear lock up at 30mph minimum. So my car runs higher rpm at speeds of 25mph then it does at 60mph. (along with most GM AT's, at least before much more current models)

 

[ROAD_DOGG33J]

Hmm... thats bad! Oil Consumption? Emissions?

That's actually pretty good.

Only problem is that me and my dad saw some oil crud in the anti-freeze(it's possible that it's just some oily product the previous owner put into the radiator to stop a leak). Since then me and my dad flushed the system out and filled it with water for the summer. I plan on checking the anti-freeze the next time I fill the car up though just to make sure.

Sounds like a bad intake manifold gasket. Someone probably poured in the wrong coolant and the owner offloaded it on you.

 

[homeforsummer]

It seems to me like that's to arbitrary with little or no regard for weight.

Weight has significantly less bearing on cruising economy than it does on acceleration, braking and cornering. Two cars with the same engine and gearing will use roughly the same amount of gas cruising at 40mph, even if one is 400 lb heavier. It'll have taken more energy to get it up there (and as such city MPG might suffer) but to keep it going the effect of weight isn't that great.

Also keep in mind, these numbers are (apparently) for flat roads, while I know of and have driven places where flat roads dominate, it's certainly not an "everywhere" thing. The hillier it gets, the more momentum wins.

True. In scenarios where you're driving up hill, your "minimum revs" to keep going without changing down might need to be higher so the hill doesn't slow you as much.

Ideally going up hill you're supposed to back off and accelerate downhill to make use of gravity, but there are certain situations where it's beneficial to use a bit more speed up hills so you don't need to change down and use more revs. Also, the less time you spend on a hill, the less fuel you use going up it!

But you're right, hilly regions skew fuel efficiency figures - though official tests can't account for everything.

4, but from other posts it's been said with different or quicker gearing some cars can manage better mileage at lower speeds, whereas my car has a hard time pulling at the "beginning" of third and fourth (roughly 1400rpm), at any speed third does not manage the mileage fourth does. But that may be due to my hilly conditions, hard to say.

It could be the hills, and it could be the way your car develops its torque. If your car has a hard time pulling below 1400rpm then for the purposes of accelerating you're best changing down to account for this, but in theory on a perfectly flat road (and certainly down a hill) your car should get decent economy at less than 1400rpm, in any scenario you aren't needing to accelerate.

Again in theory, on a flat, smooth road, you should be able to trickle along virtually at tickover in top using very little fuel - but if you need to accelerate, trying to do so would be quite inefficient as the engine would be labouring too much.

If more moronic means "majority" I agree.
But they could have "gentle" "average" and "aggressive" readings, since city driving is where people and cars suffer the worst mileage, it seems more important to me to focus on improving peoples city driving habits rather than rural and highway.

Gentle, average and aggressive readings would be good, but there passes a point where you begin to make stickers like Niky's suggestion a bit too complicated for the average Joe. I'd expect that if someone can hit the MPG figures for 50, 60 and 70mph when cruising but are way off on the city reading, then they can put that down to either particularly bad city traffic or particularly bad driving!

Of course some cars are just flat out screwed by their transmissions (mine) in the city, where even on flat roads 2000 rpm is unavoidable until it reaches third gear lock up at 30mph minimum. So my car runs higher rpm at speeds of 25mph then it does at 60mph. (along with most GM AT's, at least before much more current models)

That's one of the things I like about my car and a reason I can hit the official averages so easily. It's not the most economical motorway car because the gearing is quite low, but conversely in the city that low gearing means it's quite happy pottering around at 30mph in top (6th) a lot of the time as long as the traffic is flowing. As you can imagine this is pretty good for city economy.

The other thing of course is that with your auto transmission, the economy is much harder to account for anyway. I missed if you originally said your car was auto somewhere but I've been assuming manual the whole time.

All but the latest autos are fairly inefficient compared to a well-driven manual, simply because they're never quite in the gear you want them to be in.

On the flip side, I know I'd forgo the fuel efficiency benefits of a manual for the ease of an auto in the city sometimes...

 

[nick09]

My dad told me he used a thinner synthetic blend oil since the car ran fine. I think my dad told me it was 5W20 compared to the 5W30 oil the manual says.

How would a bad intake manifold gasket flood the antifreeze(not that smart on working on cars)?

 

[ROAD_DOGG33J]

The gasket lets coolant into the oil and vice-versa. You could also find white stuff in the oil if that's the problem. Look up malibu intake manifold on google.

 

[nick09]

The gasket lets coolant into the oil and vice-versa. You could also find white stuff in the oil if that's the problem. Look up malibu intake manifold on google.

Found no white stuff in the oil when I checked it cold. I also checked the coolant reservoir and the thing was low in water down to the bottom and the underside of the cap had that mucky crap and oil around the rubber seam. I've also checked the intake manifold on top of the engine and it's not stock. I've also looked under the cap on the engine and I see no white stuff anywhere.

This does not sound good and it lines up with problems that other Malibu's have.

 

[TheBook]

I thought that would be the head gasket, if he's seeing coolant in the oil/vice versa...

 

[Eric.]

My Grand Am (with the 3.4L V6) had the intake gaskets go out and the result is peanut-butter looking coolant. Why manufacturers use plastic-anything inside an engine astonishes me. Nick, replace those with METAL ones. They'll cost a bit more but should never need replaced, whereas you'll probably be doing the plastic ones every few years. The mechanic that changed mine knew exactly what the problem was and said he's changed them on dozens of Grand Ams in town. And multiple times for those who went with the plastic replacements.

Shortly after, mine blew the headgaskets and then the intake gaskets again. And then I bought a Civic.

 

[CSLACR]

Found no white stuff in the oil when I checked it cold. I also checked the coolant reservoir and the thing was low in water down to the bottom and the underside of the cap had that mucky crap and oil around the rubber seam. I've also checked the intake manifold on top of the engine and it's not stock. I've also looked under the cap on the engine and I see no white stuff anywhere.

This does not sound good and it lines up with problems that other Malibu's have.

Head Gasket. Maybe both, fix ASAP.

My Grand Am (with the 3.4L V6) had the intake gaskets go out and the result is peanut-butter looking coolant. Why manufacturers use plastic-anything inside an engine astonishes me. Nick, replace those with METAL ones. They'll cost a bit more but should never need replaced, whereas you'll probably be doing the plastic ones every few years. The mechanic that changed mine knew exactly what the problem was and said he's changed them on dozens of Grand Ams in town. And multiple times for those who went with the plastic replacements.

Shortly after, mine blew the headgaskets and then the intake gaskets again. And then I bought a Civic.

Head gasket was the real problem, and your mechanic "knew" wrong. Notice your intake manifold gaskets "needed" replaced again. A blown head gasket will warp the heads if overheated, which will cause the intake manifold gasket to fail from warping. If the head(s) (depending) warped, the new head gasket will also fail quickly, you're lucky to have rid yourself of the problem, though unlucky for the poor sap that bought it, who is probably the biggest victim. I won't say it's impossible for an intake manifold to mix coolant and oil, just highly unlikely in any event.

This is why I fix my cars whenever possible, as a mechanic will never admit to having fixed the wrong thing, because then (gasp) they'd have to fix their faulty work for free.