many 4 cylinders make so much more power and torque at higher RPM's, even with the same gas pedal position, that it has never surprised me that i can equal my car's claimed highway MPG rating on 80 MPH trips, even including triple digit blasts. slowing down kills my mileage to the tune of 20%! the other thing is that the faster you drive...
A) your engine has to power the A/C compressor and electrics for less time, and therefore less gas is used on those things.
B) your A/C will be far more effecient at higher speeds, and therefore spend less time cycled on, further reducing the A/C's impact on MPG. in some cars, you can feel a distinct difference in vent temperature between even 50 MPH and 70 MPH.
C) as a percentage of your vehicle's total power requirements, A/C and electrics drop dramatically the faster you drive. if it takes 15 HP to cruise at 30 MPH and the A/C uses 5 HP, running the A/C requires a whopping 33% increase in engine power. at 80 MPH, where you might be using 75 HP, suddenly the A/C only requires a 7% increase in power. so again, driving fast vastly reduces the impact of the A/C and electrics on your mileage.
on mountain trips, maintaining a high rate of speed is CRUCIAL to my mileage, because it means i can use momentum to carry me over inclines without having to dig deep into the accelerator, and because slowing down results in my car being forced to kick down one or even two gears. on trips where traffic screws me up, even if i don't have to touch the brakes often, my mileage suffers by about 20% because i end up screaming up a hill at 5,000 RPM trying to keep up with traffic instead crusing serenely over it at 20 MPH faster with no drama and no floored gas pedal.
A) your engine has to power the A/C compressor and electrics for less time, and therefore less gas is used on those things.
B) your A/C will be far more effecient at higher speeds, and therefore spend less time cycled on, further reducing the A/C's impact on MPG. in some cars, you can feel a distinct difference in vent temperature between even 50 MPH and 70 MPH.
C) as a percentage of your vehicle's total power requirements, A/C and electrics drop dramatically the faster you drive. if it takes 15 HP to cruise at 30 MPH and the A/C uses 5 HP, running the A/C requires a whopping 33% increase in engine power. at 80 MPH, where you might be using 75 HP, suddenly the A/C only requires a 7% increase in power. so again, driving fast vastly reduces the impact of the A/C and electrics on your mileage.
on mountain trips, maintaining a high rate of speed is CRUCIAL to my mileage, because it means i can use momentum to carry me over inclines without having to dig deep into the accelerator, and because slowing down results in my car being forced to kick down one or even two gears. on trips where traffic screws me up, even if i don't have to touch the brakes often, my mileage suffers by about 20% because i end up screaming up a hill at 5,000 RPM trying to keep up with traffic instead crusing serenely over it at 20 MPH faster with no drama and no floored gas pedal.
Yep.
My Turbo 4cyl saab gets better milage in the city then our C5 vette. But the vette gets better milage when going over 65mph.
Way to many factors to say all car gets better milage over 60+. Maybe some will but not by much. 55mph will usually be better as you will be going fast enough to be in high gear but not to fast to wind the engine up.
Zenmervolt
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The precise speed for highest efficiency varies from vehicle to vehicle. For most modern cars, however, the speed at which maximum fuel efficiency occurs is between 35 and 45 mph in the top gear ratio.
Essentially, the best fuel mileage will occur at the lowest speed practical in the transmission's highest gear.
ZV
Essentially, the best fuel mileage will occur at the lowest speed practical in the transmission's highest gear.
ZV
Zenmervolt
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Wrong. Maximum fuel efficiency occurs when large throttle openings are used while short shifting. Testing done by BMW in the 1980's proved that accelerating with 75-80% throttle while shifting at 2,000 RPM yielded the greatest fuel efficiency. The reason for this is because at small throttle openings increase pumping losses and force the engine to work against the throttle butterfly, which robs a large amount of power (this is also a main reason that diesel engines are more efficient; they do not have a throttle valve). Using 75-80% throttle minimises pumping losses without invoking the full-throttle fuel enrichment mapping that the ECU uses to richen the mixture at 100% throttle.
The most efficient way to do things is to shift as soon as possible and have a heavy foot on the accelerator and let the car torque itself down the road.
ZV
Zenmervolt
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Wrong. RPM is the largest player in fuel consumption. Throttle opening is vastly more important. It's more efficient to run 50% throttle at 1,800 RPM than it is to run 25% throttle at 3,000 RPM.
You can claim it to be a misconception all you like, but testing proves your view to be incorrect.
ZV
No, according to the thread that says what song was #1 on your b-day, (TLC- Unpretty) I'm actually 7.
In reference to C, thats not only because of momentum but because of powe curve and w/the gear ratio...
newParadigm
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- Jul 30, 2003
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Exactly, which is why my Mazda 626 5 Speed does best at around 85->4250 RPM (peak torque). That torque point was even more valuable at the auto cross last weekend though.
Zenmervolt
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Wrong, wrong, wrong.
Peak torque is maximum POWER efficiency. This is NOT the same as maximum fuel efficiency. At peak torque, an engine is making the most power per unit of fuel ASSUMING WIDE OPEN THROTTLE. If you aren't using large amounts of throttle, then the engine's fuel efficiency falls off dramatically, as does the amount of power produced. In other words, that documented torque peak is only the torqe peak if you have your foot to the floor, if you don't have your foot to the floor, the engine's power curve (and therefore the torque peak) changes.
An automobile achieves the greatest mileage in the highest gear, with a large throttle opening at low RPM. Note that the optimum fuel mileage for the vehicle is NOT achieved at the same point as the engine's most efficient point for turning fuel into power.
ZV
no scientific proof but from my experience more RPMs = more gas used. And 2,000 RPMs is usually the most efficient.
Zenmervolt
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http://www.roadandtrack.com/article.asp...ion_id=20&article_id=3424&print_page=y
Note that the author is a member of the Society of Automotive Engineers.
From the article (emphasis added):
"The most efficient way to reach cruising speed is wide-open-throttle (WOT) short-shifting. That is, not only do revs cost money, but so does prolonged motoring in lower gears, when throttling and pumping losses are their greatest.
WOT/short-shifting can save as much as 20 percent in city driving, worst to best case. In actual practice, rarely does traffic allow full WOT, but it's certainly fun ? and efficient as well ? to accelerate briskly through the lower gears to whatever the ambient speed happens to be.
Once there, the appropriate choice of gear is the one that offers modest rpm with relatively large (and constant!) throttle."
ZV
- Mar 20, 2000
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peak torque is the greatest volumetric efficiency for a heat engine.
the thing goku is leaving out is that while peak torque gets the most done for any amount of fuel spent, at higher speeds peak torque might be pushing tons (literally) of air. which isn't particularly useful when you're trying for peak gas mileage.
Somebody has to do a conclusive point-to-point test...not guesses based on what your car's instantaneous mileage meter shows.
Even the linked Road and Track article does not include an actual test (Mind you, this quote: "Power requirements grow with the square of vehicle velocity" should be pretty damning to the OP's case)
How hard would it be for a magazine to test, anyway? Two drivers in one car on a deserted highway (Two drivers so drivers can do 4 legs and don't need to take nap breaks and deserted highway so traffic doesn't muck up the mileage). Fill the tank, get on the highway, set cruise at 55, and drive until the fuel gets close to empty. Record. Fill the tank, get on the highway, set cruise at 75, and drive until the fuel gets close to empty. Record. Repeat each test 10 times.
Repeat for different cars too if you'd like...
The world needs a definitive test
Even the linked Road and Track article does not include an actual test (Mind you, this quote: "Power requirements grow with the square of vehicle velocity" should be pretty damning to the OP's case)
How hard would it be for a magazine to test, anyway? Two drivers in one car on a deserted highway (Two drivers so drivers can do 4 legs and don't need to take nap breaks and deserted highway so traffic doesn't muck up the mileage). Fill the tank, get on the highway, set cruise at 55, and drive until the fuel gets close to empty. Record. Fill the tank, get on the highway, set cruise at 75, and drive until the fuel gets close to empty. Record. Repeat each test 10 times.
Repeat for different cars too if you'd like...
The world needs a definitive test
NaOH
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- Mar 2, 2006
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It says to get through your low gears quicker so that you don't spend as much time revving in them (RPMs). You need to get through your lower gears so that you have speed to MOVE in the higher gears. Lower gears rev higher so get through them quickly so y ou can cruise in higher gears which don't rev as high. Rev = RPM = Waste gas = You fail Reading comprehension
I dunno, I agree that my car is certainly different than most, but I get around 32MPG whether I'm cruising down the highway at 65, or carving canyons while redlining every gear. It's only when my speed drops below 30MPH (like in the city) that my mileage drops below 30 or so. I was surprised to...every other car I've driven, you stay as far below that redline as possible if you want good mileage.
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