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Overboost... ? Turbo power

Discussion in 'A3/S3 Forum (8L Chassis)' started by mordz, Apr 30, 2007.

  1. mordz
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    mordz Audi S3 (2000)

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    [Apr 30, 2007]
    Hi Guys,

    I have seen ... and no doubt so have you, the advert for the new astra VXR.

    My question is.. what is Overboost? the advert for this VXR says it has an 'overboost' feature.

    from reading posts my understanding what this is a fault not feature?! however after a bit of googling found that its a point when the turbo can momenteraly force more oxygen into the chaimbers thus giving an 'overboost' above its normal operating spec?!

    another question regarding the turbo on the S3.. i have read a post saying that the boost dies off around 3000rpm and this is an 'issue' my car has always been like this. i guessed it was the lag while the turbo spooled up - learning to drive the car poperly you can always be in the 'boost' is this the case or does it need looking at.

    ta dudes.
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  3. Blunteh
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    Blunteh Member

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    [Apr 30, 2007]
    Is your S3 remapped ?
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  4. mordz
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    mordz Audi S3 (2000)

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    [Apr 30, 2007]
    bloody hope not... it was bought as a totaly un modified model.. but i did plan to do it.

    i will be gutted if its already running at full pelt. its started to feel slow.

    is there a way to check?
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  5. scib4
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    scib4 Beep-Beep!

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    [Apr 30, 2007]
    Get it on a Dyno :icon_thumright:
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  6. Blunteh
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    Blunteh Member

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    [Apr 30, 2007]
    2ndly... has the MAf ever been changed ?


    BTW I thought/vagually remember/dreamt/imagined/(insert any other possibility) the overboost was like a mini remap where they allow you to use the engine at a higher state of tune for a limited time period. (It waits for a set period before allowing you to do it again).
    #5
  7. Blunteh
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    Blunteh Member

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    [Apr 30, 2007]
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  8. mordz
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    mordz Audi S3 (2000)

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    [Apr 30, 2007]
    maf never been change to my knowlage.. (nothing in the history) i take it its not normal for a sudden boost to pick up just at 3000rpm and die off arround 6500rpm?

    yes same as corsa from that quote, whats all that about? does it have a button?
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  9. mordz
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    mordz Audi S3 (2000)

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    [Apr 30, 2007]
    sorry for being a dump ass n00b, but whats that? and where can i take it for it checking? will VAGCOM read anything off?
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  10. madvw
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    madvw Active Member

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    [Apr 30, 2007]
    another word for dyno is "rolling-road" - can be used as a way of calculating the power output of your car.

    There is a spreadsheet available for excel too, albeit a bit inaccurate, but suprisingly good too... have a google on butt-dyno (i think... could get some dodgy hits with that one...) Using that, with logged output from VAG-COM, you can calculate your BHP output.
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  11. Blunteh
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    Blunteh Member

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    [Apr 30, 2007]
    Dyno - rolling road Mordz...

    About your power curve.... that sounds fairly normal... if it feels like it's hesitating it could be the MAF though (mine was)

    As for the VXR overboost thing.... no idea, I assumed it was a button....
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  12. rodenal
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    rodenal Active Member

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    [Apr 30, 2007]
    Also your turbo suddenly kicking in at 3000 rpm isnt really normal, does the car hesitate, then suddenly go? sounds maf related if so.

    The overboost facility on the vauxhalls is just the car very temproarily making the turbo work harder, but only for a few seconds so as not to damage it - its nothing special tbh. As far as im aware the S3's dont have an overboost facility.
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  13. TheSpaceCowboy
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    TheSpaceCowboy Member

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    [Apr 30, 2007]
    I assume with the overboost it just forces the turbo to run near maximum boost, although I'm sure it's running below the actual maximum what with tolerances on modern cars.
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  14. mordz
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    mordz Audi S3 (2000)

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    [Apr 30, 2007]
    Hi guys, thanks for the info MAF seems to be an issue that pops up a few times. ill dissconnect it and see if it makes a differance when i get the car back this weds.

    as far as hessitation etc... if i set of in 1st it goes like a normal (none performance car) as soon is i hit 3000rpm the power is delivered throwing you back in the seat..(though if you listen to the engine it does kind of wind up to it) although its great fun i would have thought for an inexperianced driver its rather unsafe and cant be right ?! i dunno.

    hehe reminds me for doc brown and the magic 88mph "jumping giggawats"

    its the same in most gears, seems to come from nowhere and bite you suddenly at 3k.

    the seller said its how it was designed blah blah - him being a traffic cop, i believed him
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  15. TheSpaceCowboy
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    TheSpaceCowboy Member

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    [Apr 30, 2007]
    Mordz I'm not sure if its the same on the S3 having no real experience, but on the few turbo cars I've driven there is normally a certain amount of turbo spool up where the turbo doesnt kick in with any kind of power until you reach a certain rev range.
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  16. mordz
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    mordz Audi S3 (2000)

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    [May 1, 2007]
    thanks space cowbow, this does seem to be whats happening...

    maybe someone else with an S3 can confirm?
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  17. Blunteh
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    Blunteh Member

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    [May 1, 2007]
    It shouldn't be *that* pronounced on a stock mapped S3 (IMHO)
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  18. sitrials
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    sitrials Member

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    [May 1, 2007]
    yeah my S3 remapped to 265 really kicks you back in the seat when the turbo kicks in! but then my friends evo 6 did this and blew his turbo up as it was running way to lean!
    but i've always found with turbo'd cars you get a sudden surge more so if its been remapped as the boost pressure has been increased with the fueling!
    get it on a dyno and have a healthcheck on your motor!
    or another way is fitting a boost gauge, then see what its running i'm sure someone knows what a standard S3 will run at mine is 18psi peak
    they will both cost about the same! but the boost gauge you can do yourself!:icon_thumright:
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  19. mordz
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    mordz Audi S3 (2000)

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    [May 1, 2007]
    Thanks guys,

    It does drink too 22mpg average.

    it needs to go in after the respray anyway as the ARB bush's need doing. ill get them to check then. i was also going to fit a boost gauge anyways.

    ill let you know what i find, does anyone know a decent place to get it dyno'd in leeds?
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  20. TheSpaceCowboy
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    TheSpaceCowboy Member

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    [May 1, 2007]
    Hi Mordz, I think 22mpg is around what you would get, you may get a little higher if you drive sensibly, I was told to expect 14 mpg out of my car (1.8 N/A) but are you booting it about every now and again? I get around 280 - 330 miles from a tank (55 litres) depending on how I drive and what fuel I have in the car. Hope that helps put it in perspective!
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  21. rodenal
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    rodenal Active Member

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    [May 1, 2007]
    Ehhhh 14mpg out of a 1.8n/a - what planet was the guy that told you that on - you should never see any less than 25 even being mean to it, and you should be able to get 35-40 on the motorway
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  22. TheSpaceCowboy
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    TheSpaceCowboy Member

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    [May 2, 2007]
    I know he was on a different planet, you'd get better mileage out of an Aston Martin Vanquish if that were true! Not sure if your talking about my car or the S3 but I get less than 25 if I really gun it about, I've never got 40 mpg out of it either, it had an audi service 6000 miles ago.
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  23. mordz
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    mordz Audi S3 (2000)

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    [May 2, 2007]
    i drive fast, (ended up tuning off the instant mpg computer coz i dont like what im seeing) though i have never got 30mpg on motorway - 28-29mpg.
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  24. foolish3uk
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    foolish3uk Member

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    [May 4, 2007]
    i average 23 mpg even after blasting around in it all the time.
    the turbo cuts in at about 2,500 rpm and goes to full boost, if you have any lacks of power or anything then i recommend that you replace the air mass meter first.
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  25. mordz
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    mordz Audi S3 (2000)

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    [May 5, 2007]
    having got it back it does seem to wind up at 2.5k then be fully boosted at 3k. maybe its pronounced to me as im used to driving a hyundi shed!?
    #24

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