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Which uses more gas?

C

clickynext

Platinum Member
If you're making the same amount of torque, what uses more gas, being in a higher gear and depressing the gas pedal more, or being in a lower gear and depressing the pedal less? Talking about a manual, in case it makes a difference.
 
I think its better to be in a high gear with lower RPM... I think you use up less gas than driving in a lower gear(at the same speed)... not sure... just stuff you hear here and there...
 
Originally posted by: StevenYoo
isn;t it only based on RPM, not what gear ur in?

blablablablablablabla is right methinks
Click to expand...

i dont believe so, because if you are in a High gear (one which is to high) and you are bogging the engine by flooding it with fuel, you are just WASTING fuel. because the engines RPMS are not high enough to cause all the fuel to explode thus exhausting wasted fuel.
 
Depends on the situation, but if you're going up a hill, being in a lower gear saves you gas. Fuel mileage is more dependant on throttle position rather than engine speed. You can be coasting down a hill at 85mph at 4000rpm and waste less gas than going up a really steep hill at 2000 rpm with the gas floored.
 
Originally posted by: MIKEMIKE
Originally posted by: StevenYoo
isn;t it only based on RPM, not what gear ur in?

blablablablablablabla is right methinks
Click to expand...

i dont believe so, because if you are in a High gear (one which is to high) and you are bogging the engine by flooding it with fuel, you are just WASTING fuel. because the engines RPMS are not high enough to cause all the fuel to explode thus exhausting wasted fuel.
Click to expand...


TRUE... but anyone who drives a manual car knows(i hope) that you shouldnt do that, you can ¨feel¨ when the engine is on a gear that is too high and therefore wasting fuel..

My experience tells me that you waste the most fuel when you drive recklessly(like used to) for example unnecessarily speeding in short distances(or in traffic), then braking and speeding up again, over and over again... its better to just keep a ¨constant¨ speed, and preferably drive at around 3000 RPM or so..
 
Originally posted by: d33pt
Depends on the situation, but if you're going up a hill, being in a lower gear saves you gas. Fuel mileage is more dependant on throttle position rather than engine speed. You can be coasting down a hill at 85mph at 4000rpm and waste less gas than going up a really steep hill at 2000 rpm with the gas floored.
Click to expand...

But we're talking the engine is making the same amount of torque in both situations, here. If it were coasting down a hill, chances are it's not making any torque, and I heard that fuel consumption in that case is effectively nill.
 
Originally posted by: blablabla
Originally posted by: MIKEMIKE
Originally posted by: StevenYoo
isn;t it only based on RPM, not what gear ur in?

blablablablablablabla is right methinks
Click to expand...

i dont believe so, because if you are in a High gear (one which is to high) and you are bogging the engine by flooding it with fuel, you are just WASTING fuel. because the engines RPMS are not high enough to cause all the fuel to explode thus exhausting wasted fuel.
Click to expand...


TRUE... but anyone who drives a manual car knows(i hope) that you shouldnt do that, you can ¨feel¨ when the engine is on a gear that is too high and therefore wasting fuel..

My experience tells me that you waste the most fuel when you drive recklessly(like used to) for example unnecessarily speeding in short distances(or in traffic), then braking and speeding up again, over and over again... its better to just keep a ¨constant¨ speed, and preferably drive at around 3000 RPM or so..
Click to expand...

If, by bogging you mean to the point where it is stuttering then, yes this is wasting fuel. However, engines are the most efficient when they are at WOT, or not creating vacuum. That is why you can get a rough idea of your fuel economy with a vacuum gauge. My grandfather's RV had one of these, they give a good idea of fuel consumption. Now obviosuly in heavy traffic, or highway cruising you can't be using WOT very much, so this point is moot. Also the Toyota Prius only runs the engine when it knows it will have enough load from the electric motor to make the engine run at minimal vacuum.
 
Depressing the gas pedal more uses more gas.

The gas pedal is linked directly to the throttle plate, and the farther the gas pedal is depressed, the farther the throttle plate opens, and the more air is allowed into the engine.

The purpose of a carburator or a fuel injection system is to maintain the correct ratio of fuel to air going into the engine. A stoichiometric mixture is roughly 14:1 air to fuel. So, the car is going to do its best to use 1/14th as much fuel as the amount of air let into the engine.

Therefore - the more air getting in, the more fuel used. All the gas pedal does is control the amount of air let into the engine, so the less pressure on the gas pedal - the less fuel used.
 
Originally posted by: blablabla
Originally posted by: MIKEMIKE
Originally posted by: StevenYoo
isn;t it only based on RPM, not what gear ur in?

blablablablablablabla is right methinks
Click to expand...

i dont believe so, because if you are in a High gear (one which is to high) and you are bogging the engine by flooding it with fuel, you are just WASTING fuel. because the engines RPMS are not high enough to cause all the fuel to explode thus exhausting wasted fuel.
Click to expand...


TRUE... but anyone who drives a manual car knows(i hope) that you shouldnt do that, you can ¨feel¨ when the engine is on a gear that is too high and therefore wasting fuel..

My experience tells me that you waste the most fuel when you drive recklessly(like used to) for example unnecessarily speeding in short distances(or in traffic), then braking and speeding up again, over and over again... its better to just keep a ¨constant¨ speed, and preferably drive at around 3000 RPM or so..
Click to expand...

3000 RPM?

Who in the world drives around with their motor running that high? I drive 100+ miles per day around town and the highway, I bet I dont break 3k RPMs 15 times and that includes getting on the highway and taking off from stoplights.

If I drove on the highway at the RPM you want I would be going well over 100MPH.
 
Originally posted by: MIKEMIKE
Originally posted by: StevenYoo
isn;t it only based on RPM, not what gear ur in?

blablablablablablabla is right methinks
Click to expand...
i dont believe so, because if you are in a High gear (one which is to high) and you are bogging the engine by flooding it with fuel, you are just WASTING fuel. because the engines RPMS are not high enough to cause all the fuel to explode thus exhausting wasted fuel.
Click to expand...
Yes, fuel metering is dependant upon engine load as well as RPM, however, you are NEVER dumping in more fuel than is necessary at a given RPM unless something is wrong with your fuel metering system, even with a carburetor. Carb or FI will, when adjusted and functioning properly, always maintain an acceptable ratio of fuel to air and there will be no more residual unburned hydrocarbons than normal, at least, not from gasoline.

However, "lugging" an engine at too low of an RPM does cause a bit more oil blow-by, and the oil will make its way into the combustion chamber to be burnt, which is why some cars with marginal piston rings will smoke when going uphill.

That said, as long as you are not lugging the engine below its powerband, (which is really only a concern from an engine longevity standpoint than a fuel consumption standpoint) you will use less fuel in a higher gear at a lower RPM.

Engine load contributes to fuel consumption, but RPM is far and away the larger factor. That's why my 3,800 pound Lincoln with a big V8 gets 26-28 mpg on the freeway with the engine turning 2,000 RPM while my 951, which makes comparable crank HP numbers from its turbocharged I4, only gets 25 mpg on the freeway with its engine turning 3,000 RPM.

ZV
 
Originally posted by: notfred
All the gas pedal does is control the amount of air let into the engine, so the less pressure on the gas pedal - the less fuel used.
Click to expand...
No. All the gas pedal controls is the size of the opening through which air can enter the engine. WOT at 2,000 RPM flows A LOT less air than WOT at 3,000 RPM. Yes, WOT will use more fuel, but as I said before, the effect of throttle position is absolutely dwarfed by the effect of RPM.

ZV
 
Originally posted by: Sluggo
3000 RPM?

Who in the world drives around with their motor running that high? I drive 100+ miles per day around town and the highway, I bet I dont break 3k RPMs 15 times and that includes getting on the highway and taking off from stoplights.

If I drove on the highway at the RPM you want I would be going well over 100MPH.
Click to expand...
3,000 RPM in my 951 is just a touch over 80 mph. That's cruise speed on the freeway.

ZV
 
Originally posted by: Zenmervolt
Originally posted by: Sluggo
3000 RPM?

Who in the world drives around with their motor running that high? I drive 100+ miles per day around town and the highway, I bet I dont break 3k RPMs 15 times and that includes getting on the highway and taking off from stoplights.

If I drove on the highway at the RPM you want I would be going well over 100MPH.
Click to expand...
3,000 RPM in my 951 is just a touch over 80 mph. That's cruise speed on the freeway.

ZV
Click to expand...

80MPH in my worn out Chevrolet results in about 1700 RPM, even if I turn off OD, I still dont think it will kick up to 3000.

I think my Expedition turns even lower than 1700 at 80, but it does have taller tires.
 
Originally posted by: iamtrout
Originally posted by: Sluggo
If I drove on the highway at the RPM you want I would be going well over 100MPH.
Click to expand...

100+ mph @ 3K RPM? Impossible.
Click to expand...

I'm not even sure the motor would produce enough torque to push the truck through the wind resistance @100 in OD, but I'm sure the RPMs would not climb above 3000 if you could leave it in OD.
 
Well obviously the gearing depends on the car. My Mazda Protege5 gets close to 3000 RPM at just over 100 km/h (pretty much the fastest I ever go around here).
 
There is a specific RPM where your engine gets optimal fuel economy. Lets assume for your car that's 2000 rpm. It takes a certain amount of power to keep your car moving constantly at 60mph. The closer you are to 2000rpm, the less fuel you need to produce that amount of power.

The optimum fuel efficiency rpm is usually way below the optimum power RPM, so you're usually better off in high gear.
 
Originally posted by: Zenmervolt
Originally posted by: notfred
All the gas pedal does is control the amount of air let into the engine, so the less pressure on the gas pedal - the less fuel used.
Click to expand...
No. All the gas pedal controls is the size of the opening through which air can enter the engine. WOT at 2,000 RPM flows A LOT less air than WOT at 3,000 RPM. Yes, WOT will use more fuel, but as I said before, the effect of throttle position is absolutely dwarfed by the effect of RPM.

ZV
Click to expand...

The size of the throttle opening is what regulates RPM. If you decrease the size of that hole, then RPM is going to go down. RPM increases when you make the size of that hole bigger.

What the car does at WOT is pretty irrelevant since you nver drive like that for more than a few seconds as a time. Even if you wanted to, you'd just be bouncing off the rev limiter all the time.

Your point is only valid at all during acceleration, and I don't think that's what the OP was asking. I think he basically wanted to know if 2000RPM in 5th gear used more or less gas than, say, 2800RPM in 4th gear at cruising speed.
 
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