Chris NottJMB Retrofits
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  1. #1
    JamS3's Avatar
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    Boost Via Demand??

    Can anyone clarify whether or not the level the S3 boosts is dependant upon how fast NOT how hard the accelerator pedal is pressed down via the foot?

    I'm sure I read somewhere that this was the case either in a car magazine or the S3 brochure itself when it first came out.

    Mine seems to boost alot more aggresivly when the accelerator pedal is pressed down quick, not even to full throttle as opposed to pressing it all the way to the floor slow.

    Thanks in advance

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  3. #2
    RAPS3's Avatar
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    Re: Boost Via Demand??

    Cant help on this one Jamie. If it were a cable mechanism I would say it all depends on how far you pushed the throttle. But with all the DBW and ECU gubbins I wouldnt have a clue.

    I'm sure Glen, David or Rich will be able to comment.

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    Re: Boost Via Demand??

    Glen, David or Rich????.......

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    Re: Boost Via Demand??

    Sorry I'll explain - Ess-three, David R and Rich seem to have a greater understanding of all things boost related.

    The more I think about it though, the more I would be inclined to say it would be relative to how much you pressed the pedal rather than how quick. More throttle = more fuel/air = more boost.

    If you only pressed the throttle 3/4 of the way albeit more quickly you'd still only a lesser amount of juice.

    However if you pressed it slower then you may not put as much load on the engine and hence less boost would be called upon.

    Oh bugger I dont know - HELP anyone??

  6. #5
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    Re: Boost Via Demand??

    I'll let you off just cause it's getting late....I knew who they were, I was just inviting them to reply!!

    I'm sure it was the S3 brochure (I think!) that it was dependant upon how fast the pedal was pressed down hence how much boost/aggressive acceleration was delivered ie to get yourself out of a tight spot.

    Just seems mine is dependant on this. Been doing alot of test driving with mine and it is definately better pressing the accelerator down quickly about 1/2 to 3/4 of the way down as opposed to gradual pressing all the way down to the floor.

    With the fast pressing it really takes off and gives the chacteristic kick in the back and the slow press all the way down gives more smoother acceleration without the kick, just seems to rev quite freely without loads of boost.

  7. #6
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    Re: Boost Via Demand??

    Think it was something like with the drive by wire the ECU senses how quick the accelerator has been pressed and delivers the boost accordingly

    Can anyone clarify?

  8. #7
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    Re: Boost Via Demand??

    Its determined via manifold pressure, air speed and throttle position. Obviously temperature is involved, but assume the engine is up to temp.

    When you open the throttle quickly there is a sudden pressure rise with a "gulp" of air.
    A manifold absolute pressure sensor(MAP, note not MAF) which is mounted on one of the intercoolers detects this pressure change and mentions to the ECU that something is up.

    The ECU then tells the N75 valve that you wanna go fast are going to need some extra help (requested boost).
    The N75 converts the ECU's signal to vacuum that pulls on the actutor and wastegate to spool the turbo and then you get some action.

    Obviously at the same time the MAF, temp, MAP, knock sensors etc are monitoring the situation so the ECU knows how much ignition advance and fuel to supply as well.

    As far as I know the system doesn't measure how quickly the throttle plate turns as the MAP will know due to the pressure changes.

    DBW engines are slightly less intelligent as they do not have the MAP sensor. I think this type rely more on the MAF and throttle position. Not read up much on these (even though I have one!!).

    Hope that helps a bit, and someone correct me if I've got it all wrong :-)

  9. #8
    Ess_Three's Avatar
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    Re: Boost Via Demand??

    [ QUOTE ]
    Its determined via manifold pressure, air speed and throttle position. Obviously temperature is involved, but assume the engine is up to temp.


    [/ QUOTE ]

    Good work...
    But temperature of the inlet charge IS involved at all times....even if only to retard timing as temperature climbs.



    [ QUOTE ]

    Obviously at the same time the MAF, temp, MAP, knock sensors etc are monitoring the situation so the ECU knows how much ignition advance and fuel to supply as well.


    [/ QUOTE ]

    ...and inlet temperature, and - I'm led to believe -the ESP system is tied in, monitoring wheelspin and torque shift to maximise throttle opening vs requested throttle where there is grip available to utilise the torque..where the wheels spin, the ECU throttles back to re-gain grip - on ESP equipped card obviously.



    [ QUOTE ]

    As far as I know the system doesn't measure how quickly the throttle plate turns as the MAP will know due to the pressure changes.


    [/ QUOTE ]

    I believe it does...
    I think the system knows how quickly the throttle is opened by the drivers right foot, and will attempt to match the desired throttle opening as long as grip is available and the engine parameters are acceptable.

    Assuming all the engines parameters are OK, the ECU will open the throttle plate in line with the requested position (although it may be slower, or even faster, if all other parameters are in a healthy state)

    As for measuring how fast the throttle plate turns, the ECU knows this by having the throttle body calibrated (Adaptation in VAG Com talk) for closed and wide open - assuming the TB is not faulty the ECU then knows it's 'zero' point, and 'full span' point, and can assume with reasonable accuracy that a signal 50% of the way between will equate to 50% throttle opening.

    I believe the MAP, MAF, TB position, pedal position, knock sensor, charge temperature, coolant temperature, N75 and engine speed (and ESP inputs on such equipped cars) are all used to determine the power delivery based on the revs/fuel/ingition/boost maps.


    [ QUOTE ]

    DBW engines are slightly less intelligent as they do not have the MAP sensor. I think this type rely more on the MAF and throttle position. Not read up much on these (even though I have one!!).


    [/ QUOTE ]

    Did I read you right there?
    DBW LESS intelligent?
    Surely not...

    DBW cars have a MAP sensor...on the S3 it's in the hard boost pipe from the second SMIC to the TB.

    Look at the control algorithms for a DBW car (also an ESP car) and they are far more advanced than a non-DBW car...and far more intelligent....although the ECUs ability to regulate throttle position relative to its control parameters and not always what you want it to do, can (and do) make for slightly erratic behavoiur.



    [ QUOTE ]

    Hope that helps a bit, and someone correct me if I've got it all wrong :-)

    [/ QUOTE ]

    ...and correct me if I'm wrong too... [img]/ubbthreads/images/graemlins/smile.gif[/img]

  10. #9
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    Re: Boost Via Demand??

    [ QUOTE ]

    Did I read you right there?
    DBW LESS intelligent?
    Surely not...

    DBW cars have a MAP sensor...on the S3 it's in the hard boost pipe from the second SMIC to the TB.

    Look at the control algorithms for a DBW car (also an ESP car) and they are far more advanced than a non-DBW car...and far more intelligent....although the ECUs ability to regulate throttle position relative to its control parameters and not always what you want it to do, can (and do) make for slightly erratic behavoiur.


    [/ QUOTE ]

    I do believe he meant Throttle Cable card not DBW

    Rich

  11. #10
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    Re: Boost Via Demand??

    Yeah sorry, it was late. I was supposed to write "non DBW".

    Thanks for the extrra input Glen.

  12. #11
    imported_bantam1
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    Re: Boost Via Demand??

    OK reading this quickly at work and didn't follow much of the technical malarkey anyhow.

    What was the answer then - quick or full or what?

    Thanks,

    B.

    Fighting the corner for the mechanically inept!

  13. #12
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    Re: Boost Via Demand??

    [ QUOTE ]
    OK reading this quickly at work and didn't follow much of the technical malarkey anyhow.

    What was the answer then - quick or full or what?


    [/ QUOTE ]

    Perhaps if you'd take the time to read the answers people have given to the question, you'd learn something. [img]/ubbthreads/images/graemlins/tongue.gif[/img]

    The throttle is opened as fast as the ECU decides it is able to open it based upon parameters such as speed of throttle pedal being pushed, amount of throttle pedal travel, car speed, engine load, ambient temperature, charge air temperature, coolant temperature, grip available etc...
    It's not just a case of how far or how fast you press the pedal..the ECU opens the throttle plate as far as it needs to to produce what it decides is the best power under the conditions, at the time of the throttle being pressed.

  14. #13
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    Re: Boost Via Demand??

    So bantam1 more or less yes it does have something to do with how fast the pedal is pressed down by the right foot!!

    Mine certainly goes better like this anyway!

  15. #14
    jojo's Avatar
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    Re: Boost Via Demand??

    Not sure if it's relevant, but I'm sure the DBW throttle learns how you drive, and adjusts sensitivity to your driving style. So if you are trundling around town, you get a lazy throttle and when you are giving it the full beans, the throttle response is lightning, giving maximum throttle before the pedal is fully pressed?

  16. #15
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    Re: Boost Via Demand??

    jojo, how quick does the car learn this? I mean if you are driving lazy round town then want the "full beans" throttle does this adjust immediately or do you have to have a few attempts/do a few miles for it to re-adjust?

  17. #16
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    Re: Boost Via Demand??

    [ QUOTE ]
    jojo, how quick does the car learn this? I mean if you are driving lazy round town then want the "full beans" throttle does this adjust immediately or do you have to have a few attempts/do a few miles for it to re-adjust?

    [/ QUOTE ]

    Within a mile of brisk driving I would say, takes longer to revert back to lazy throttle....

  18. #17
    imported_bantam1
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    Re: Boost Via Demand??

    [ QUOTE ]
    [ QUOTE ]
    OK reading this quickly at work and didn't follow much of the technical malarkey anyhow.

    What was the answer then - quick or full or what?


    [/ QUOTE ]

    Perhaps if you'd take the time to read the answers people have given to the question, you'd learn something. [img]/ubbthreads/images/graemlins/tongue.gif[/img]


    [/ QUOTE ]

    [img]/ubbthreads/images/graemlins/frown.gif[/img] [img]/ubbthreads/images/graemlins/frown.gif[/img] but I've only just learned to read. Comprehension is'nt scheduled till next term.

    So the thing on the right makes it go faster then? Might try that out.

    Cheers,

    B.

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    Re: Boost Via Demand??

    uuumm,remends me of the time my TB seized ,ecu switched the car to running on less cylinders and 20mph.

  20. #19
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    Re: Boost Via Demand??

    [ QUOTE ]

    [img]/ubbthreads/images/graemlins/frown.gif[/img] [img]/ubbthreads/images/graemlins/frown.gif[/img] but I've only just learned to read. Comprehension is'nt scheduled till next term.


    [/ QUOTE ]

    You are a very funny man...

    Tell me, where is spelling and grammar on your list?
    After comprehension?

    There, there...stick in...you'll get there.

  21. #20
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    Re: Boost Via Demand??

    Told you they would know [img]/ubbthreads/images/graemlins/tongue.gif[/img]

    A most Informative post, and still useful to the newly converted Leon owner [img]/ubbthreads/images/graemlins/smirk.gif[/img]

    Regarding the ecu learning your driving style as per jojo's post, I'm sure I read somewhere that resetting the ecu had a similar effect. If after resetting it you gave it a good old thrashing it learnt the new more agressive parameters.

 

 

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