You are flat out at 7k on the rev limiter. It still takes more work for the engine to maintain a speed of 130 due to wind resistance.

The way Fuel injection works just to put it in here since I have experience tuning modern Fuel injected cars.

For fuel: The computer reads the throttle position sensor and the Air flow meter.
For ignition timing: This goes by engine load at a given RPM. I am not going to explain a advance graph. To make it easy.. the higher the load, the less ignition timing is present.
If you take away advance by giving the engine more of a load (WIND RESISTANCE!!!!!) the engine will suck in more air. More air going past the air flow meter means more fuel is let through.


So I stick to my comment. Going flat out at 130 uses more fuel than flat out at 30.

It most certainly does, but will you travel further at 30 mph than at 130? I guess no...

A claim I'd like to make is that consumption, economy, and efficiency are three different things. Consumption is the rate at which fuel is consumed, liters per minute for example. Economy is the fuel which the vehicle uses for a given distance traveled, such as liters per 100 kilometers. Efficiency is how much energy is outputted with respect to the amount of energy theoretically available in an amount of fuel, usually around 20%-30% on gasoline engines.

It's possible for one vehicle to consume more fuel than another, be more efficient, yet have worse fuel economy.

EDIT: Though, I've just realized that amp88 said that both scenarios are at 7000RPM and their rev limiters are at 7000RPM. This is not enough information to tell which is consuming more fuel if they're bouncing off the rev limiter. If there is no rev limiter, and both engines are spinning at a constant 7000RPM, full throttle, and everything else is constant (temperature, pressure, etc) then I'd say they're both using the same amount of fuel.

Full throttle is full throttle.
In newer cars more air => more fuel-usage
so the one in 5th/6th gear would run out faster than in 1st gear.

Although I think older cars will run out equally fast.

Quote from BlakjeKaas :

Full throttle is full throttle.

But throttle alone does not define how much air is going into the engine, and therefore does not determine how much fuel is being consumed. Most simply, the amount of air flowing through an engine is determined by throttle, RPM, and volumetric efficiency, neglecting the temperature of the air, etc.

The throttle is what controls the amount of air. Nothing else does directly. The Vol. Eff. isn't a controlled variable. Diesels (or throttle-less petrols) are a different matter....

I'd say that the one doing 130MPH@7000RPM runs out of fuel faster because it would need a bigger volume of mixture to mantain the 7000rpm's it is doing... But I'm a loser babyyyyyyy so why don't you kill meeeeee...

Fuel usage is dependant on how far down you put your foot, RPM has no effect on gas mileage, I can be at 8000 in 1st gear going 30 mph or like 1500 in 5th gear going 30 and I will be using the same amount of gas; IF I keep my foot in the same position no matter the gear or RPM I will be using the same amount of fuel.

Quote from tristancliffe :

The throttle is what controls the amount of air. Nothing else does directly.

But isn't the mass air flow determined by throttle and RPM, not just throttle alone? I was under the impression that throttle determines the density of the air, and the RPM determines the velocity of the air.

Yes, but the high velocity air (at higher rpms) moves for a shorter period of time. Ignoring the fact that clever design can effectively overfill a cylinder (the >100% volumetric efficiency that you refer to) because it's a very small effect in terms of this discussion, a cylinder is filled with all the air the throttle allows.

Quote from amp88 :

Scenario 1: 7000rpm, 1st gear, 30mph
Scenario 2: 7000rpm, 5th gear, 130mph

If you started both scenarios with a full tank of fuel in which would you run out of fuel quicker (in terms of time, not distance)? Or would it take the same amount of time to run out?

edit: Full throttle in both cases, the car has a soft rev limiter at 7000rpm.

Surely based on air resistance alone, the 130 MPH one has to use more fuel because of the massive more amount of drag.

Quote from tristancliffe :

Yes, but the high velocity air (at higher rpms) moves for a shorter period of time. Ignoring the fact that clever design can effectively overfill a cylinder (the >100% volumetric efficiency that you refer to) because it's a very small effect in terms of this discussion, a cylinder is filled with all the air the throttle allows.

Then why does the torque curve of engines increase until the point at which the intake valves, cylinder head, intake manifold, throttle, and air intake can no longer allow the cylinder to fill fully with air, or so I thought?

Well the inlet system eventually becomes a restrictor - i.e. for the given pressure difference, only so much air can flow into the cylinder in so little time. But these are extremes, and we're talking about a simple theoretical example (ruined by the edit addition of the rev limiter bit).

Quote from XCNuse :

Fuel usage is dependant on how far down you put your foot, RPM has no effect on gas mileage, I can be at 8000 in 1st gear going 30 mph or like 1500 in 5th gear going 30 and I will be using the same amount of gas; IF I keep my foot in the same position no matter the gear or RPM I will be using the same amount of fuel.

Not really because it takes more energy to rotate the engine faster, bearing losses increase and so on.

Shake a piston back and forth really fast in your hand and you'll notice that it's easier to do slowly Energy has to come from somewhere and in this case it's the fuel.

edit: it's not quite so simple either in fact, there's optimal piston speed for each engine depending on other things.

http://ecomodder.com/imgs/geo- ... -chart-reconstruction.gif

Quote from vari :

Not really because it takes more energy to rotate the engine faster, bearing losses increase and so on.

Shake a piston back and forth really fast in your hand and you'll notice that it's easier to do slowly Energy has to come from somewhere and in this case it's the fuel.

edit: maybe a bicycle pump would be better example

Makes sense.. but according to fuel consumption calculators put into a car it says it uses the same amount of fuel..
That energy doesn't come in form of fuel though it comes in form of heat

If the rev limiter cuts fuel (which is what most of them do, if it cut's spark, then you get explosions from the fuel/air mixture in your exhaust), then it will be cutting fuel more often at 30mph than at 130mph.

Issues at play: the ratio of power consumed internally by the engine, versus power consumed by the external forces (rolling resistance and aerodynamic drag); the faster speed covers more ground per second; ...

Bottom line is the ratio between fuel consumed per distance traveled at 30mph versus 130mph. If the car was a 1.3 liter econobox, I suspect milage would be better at 30mph. If the car was something like a Z06 (which does redline at about 7100 rpm), then it might be better at 130mph.

this is slightly avoiding the question at hand, but I feel I should mention it. Depending on the weight of the car, the car has a sweet spot for minimal gas usage. On lighter cars it is roughly 65 MPH and on heavier cars, such as trucks it is more towards 45 MPH iirc. So, the fuel usage is going to depend on the weight of the car for the most part.

Fuel consumption would be the same irrelevant of gear. If, of course, you weren't hitting the limiter. Since you are, you'll be hitting the limiter more often in 1st gear, so end up burning less. But all the time you are burning, the fuel consumption rates will match.

At least when using a simplistic model.

Edit: Yeah, what JeffR said.

Quote from roadrash17 :

this is slightly avoiding the question at hand, but I feel I should mention it. Depending on the weight of the car, the car has a sweet spot for minimal gas usage. On lighter cars it is roughly 65 MPH and on heavier cars, such as trucks it is more towards 45 MPH iirc. So, the fuel usage is going to depend on the weight of the car for the most part.

You are right about the sweet spot, but it is more to do with resistance; air resistance, rolling resistance, friction in the transmission and all other resistances acting on the car/truck. Not it's mass. Granted it's mass plays a big role in getting to the sweet spot, but once there maintaining it is the same.

Well, from what I've researched (I did it a while ago) the mass has a large part of where the sweet spot is. But true, it does rely on a lot of other things that would need to be known in order to accurately judge where you would get that sweet spot...