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Question which has been bugging me.

  • 23-02-2008 2:19pm
    #1
    Dr.Millah
    Registered Users, Registered Users 2 Posts: 582 ✭✭✭


    Hey guys.

    Right ive been questioning this to myself every time the event happens and its starting to get more on my nerves as i cant find the answer.

    I am not fortunate enough to drive a high powered car and my 1liter engine will do me fine for the next while.
    So my question is when traveling at steady speed of 50kmph in 4th gear the gradient of the road increases. As the car is now travelling up hill there is naturaly going to be a decrese in speed. By right i should rev match and drop to 3rd gear and continue on my way which being in 3rd gear will increse the fuel consumption.
    The only alternative is to plant the foot down on the accelerator while still in 4th gear and have the car slowly speed up with less accelleration.

    So im wondering which is going to use more fuel. I know the more you press the accellerator the more fuel is sent to the engine, but if there is such little increse in power what is happening to the fuels energy? is it just being expelled from the exhust or is the consumption reducesed?

    Or if going into 3rd or maybe even 2nd gear is using up more as the acceleration per second is much greater?

    This could be a very silly question but my education on engines and car mechanics is very low.

    Thanks


Comments

  • #2
    peasant
    Registered Users, Registered Users 2 Posts: 17,819 ✭✭✭✭peasant


    Very simplified:

    Lower rpm means lower fuel consumption ...the faster the engine turns, the more fuel it can (and will) burn.

    It is always more fuel efficient to be in the highest gear possible, without labouring the engine.

    Don't worry about nailing the pedal to the floor. The engine (if it's properly set up and maintained) will not suck in more fuel than it can actually use.

    The gas pedal doesn't work like a tap that just opens the flow of fuel indiscriminately (with the engine off you can stand on the gas all you like, there is no fuel dripping out anywhere) but it works rather like a valve that regulates how much fuel the engine can suck in at any time. But even with it fully open, if the engine is only turning slowly, it will only use what it needs and not all that is theoretically available.


    As I said ...very simplified ...:D modern engine management is a bit more complicated, but the basics still apply.


  • #3
    vibe666
    Registered Users, Registered Users 2 Posts: 13,016 ✭✭✭✭vibe666


    staying in a higher gear and just trying to get a good run up is your best bet.

    as peasant says, the engine will not burn more fuel than it can use.


  • #4
    Dr.Millah
    Registered Users, Registered Users 2 Posts: 582 ✭✭✭Dr.Millah


    Great! Thanks for sharing the knowledge guys.


  • #5
    DublinDilbert
    Registered Users, Registered Users 2 Posts: 5,401 ✭✭✭DublinDilbert


    peasant wrote: »
    Very simplified:

    Lower rpm means lower fuel consumption ...the faster the engine turns, the more fuel it can (and will) burn.

    It is always more fuel efficient to be in the highest gear possible, without labouring the engine.

    A very common misconception, that lower rev's mean less petrol...

    Depending on the car and the speed, sometimes it is better to climb a hill in a lower gear....

    For example in my car traveling at 100kph its more fuel efficient to climb a hill in 4th gear rather than 5th...

    When you drop to a lower gear the engine is required to produce less torque (although revs will increase) so depending on where you are on the torque speed curve for the engine it may well use less petrol.


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