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  1. #1
    A3 Sport's Avatar
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    Bit of a daft question...

    But, my friend is trying to tell me that petrol engines are stronger than diesels if driven the same. For instance, if I take a diesel to 4800RPM (red line) every gear change, and he takes his petrol to 4800RPM every gear change, I believe that the diesel will still last longer on the whole. (or if we are both on a motorway, and Im cruising along at 2500RPM in a diesel, and he's cruising along at 2500RPM in a petrol, which will last the longest?)

    Am I right.. or am I in a fantasy world?
    Last edited by A3 Sport; 4th February 2011 at 18:07.

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  3. #2
    bez101's Avatar
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    ahhhhhh what kinda petrol engine s3 s4 rs4 etc etc

  4. #3
    superkarl's Avatar
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    stronger how??
    depends on the components of the engine. but obvously diesels have a lot higher compressions and forces on internal components. so it cant really be compared. but then, take a diesel rod thats used to x amount of forces, and a petrol which will be made for less, rod for rod the diesel will likely be made to take higher stresses, and stronger.

    but if your talking about revving both engines to the same revs, the forces acting on the diesel will be greater, but the components will be stronger. and the petrol engine will be made to do the same all day long. so theres no reason why they wont last exactly the same time. bit of a silly question, or rather an inconclusive one

    standard engine vs standard engine, they are made to do what they do, and both engines should take the forces they do, so there is no reason they wont last the same. but compare individual components, the diesels require to be stronger.
    Last edited by superkarl; 4th February 2011 at 19:17.

  5. #4
    jojo's Avatar
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    You have to say 4800rpm in a diesel is like max revs, 4800 in a petrol is like mid to high revs depending on what car.

    If both cars was cruising on the motorway in top gear and doing 2500rpm, the diesel car in most cases would be doing a higher speed than the petrol car due to it's lower gearing.



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  6. #5
    superkarl's Avatar
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    speed is irrelevent, the engines are turning the same speed, the diesels engine will be under more loads inside, ie compression, tension, torques. but its made to take those stresses. unless there is an unintended weak point, both engines will run at that rpm for a very long time. its how they test the engines. and most will have to reach a benchmark miles, or hours, set by the manufacturer for them to be mass produced, likely the same benchmark if its the same manufacturer.

  7. #6
    jojo's Avatar
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    Quote Originally Posted by superkarl View Post
    speed is irrelevent, the engines are turning the same speed, the diesels engine will be under more loads inside, ie compression, tension, torques. but its made to take those stresses. unless there is an unintended weak point, both engines will run at that rpm for a very long time. its how they test the engines. and most will have to reach a benchmark miles, or hours, set by the manufacturer for them to be mass produced, likely the same benchmark if its the same manufacturer.
    I know what you mean about engine speeds and the speed of the car is irrelevant Karl, but the op posted,

    Quote Originally Posted by A3 Sport View Post
    (or if we are both on a motorway, and Im cruising along at 2500RPM in a diesel, and he's cruising along at 2500RPM in a petrol, which will last the longest?)
    Which made me think whether he knew that both cars are geared accordingly to the way they produce their power.



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  8. #7
    superkarl's Avatar
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    ahhh i see now, sorry dude

  9. #8
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    diesels dont rev as high as petrols cus they physically cant.
    the components in a diesel engine have to be stronger (and so heavier) due to the way the engine burns the diesel with a higher cr (20:1) in an explosion rather than a rapid burning (10:1 petrol).
    the weight of the componets means they cant reciprocate as fast as the lighter components in a petrol engine.

    this has no effect of the longevity of the engine as both are built for purpose.
    but, if you fitted, say standard petrol engine rods in a diesel engine i bet they'd turn banana in a short length of time!

 

 

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