Fuel Consumption Linearity

[whitestivo]

If you are doing 2000rpm in 6th, is that linear and half of consumption of doing 4000rpm in 6th? I have always wanted to know, as it doesn’t make sense that it is, it just could not be. Maybe there is a minimum duty for the injectors, then it’s linear from there? Can you let me know.

whitestivo

[ELEGNT]

if your put your car in 6th and accelerated full throttle from 2k rpm i think it would be linear (until lift) but not as severe as 200% every 2k rpm.

so in real life assuming the road was flat 2k in 6 would be around 65? this would use less but not half of what your would use at 4k. even the wind resitance at 130 odd k's is alot more u would be up in the revs a bit more ~ producing enough power that you dont need to sink your foot much at all.

but when u came to hilly country i think 2k in 6th would use more as it would nearly be labouring the engine going up hills therefor u would ahve to put your foot down more to maintain constant speed up the hill. 4k again would be more in the power range requiring less throttle.

but your L/100 would be alot less imo sitting on 4k~130

overall i dont no that was my 2 cents of dribble

[Hiro]

No, it won't be linear.

Things like VE will change with throttle opening, load will be increasing non-linearly too (drag is either exponential or related to the square of your speed, can't remember which)

[whitestivo]

VE was what I wasn't sure about that some motors operate more efficiently at different rpm. I don't fully understand why.

if a motor is doing 2000rpm and the same motor is then spinning at 4000rpm, although the rpm are doubled, my thinking now is that due to VE, the actual amount of fuel used would not be double?

I then understand, if we add drag into the equation, then the motor has to work harder at higher speed, however, i would think that would be reflected in the RPM the car would have to do to achieve a speed.

whitestivo

[Hiro]

VE was what I wasn't sure about that some motors operate more efficiently at different rpm. I don't fully understand why.

if a motor is doing 2000rpm and the same motor is then spinning at 4000rpm, although the rpm are doubled, my thinking now is that due to VE, the actual amount of fuel used would not be double?

Exactly. It may be less than double, it may be more

I then understand, if we add drag into the equation, then the motor has to work harder at higher speed, however, i would think that would be reflected in the RPM the car would have to do to achieve a speed.

whitestivo

The engine will have to work harder, yes. Remember that RPM is not directly related to throttle position, you can rev a car quite highly with very little throttle if there is no load. It helps if you break it down into two bits: to go from 2000rpm to 4000rpm you will need more throttle to get the extra air in (assuming no increase in load), and then on top of that you will need extra throttle to make more power to overcome the extra load created by drag etc.

If that doesn't work, think of it this way - you're pushing a box at a certain speed, which requires a certain amount of force. If you double the speed at which you are pushing, you have to double your effort, but then imagine that someone is pushing harder against the box in the opposite direction in relation to how fast the box is going - you have to push extra to overcome that load as well.

In that analogy, the box is the engine, the speed is RPM, the effort you put in is fuel consumption, and the person pushing against the other side is drag. That analogy ignores VE though, but you'll get the picture that there is a lot more to fuel consumption than engine speed - load, drag and throttle position are just as critical.