1st Gen R53 Cooper S ScanGauge gives odd MAP readings

Discussion in '1st Generation: 2002–06 R50, R53 & 2004–08 R52' started by Ofioliti, Jan 24, 2010.

  1. Ofioliti

    Ofioliti New Member

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    Just installed a ScanGauge and have been using it for a few days now. There is something odd with the MAP (manifold air pressure) reading.

    When the MINI is idling, MAP reads 6 psi. I am in St. Louis, where the atmospheric air pressure should be around 14 psi.

    I attached the SG to my wife's Accord and it reads 4 to 5 psi at idle, so not exactly the same, but comparable.

    When accelerating moderately hard, the MINI's MAP goes up over 20 psi. So it is measuring boost.

    The other odd thing is that when I shut off the engine and before the SG goes to sleep, the MAP reading jumps from 6 to 14 psi ! :crazy:

    Any ideas what's going on? :confused5:
     
  2. BlimeyCabrio

    BlimeyCabrio Oscar Goldman of MINIs
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    MAP is Manifold ABSOLUTE Pressure.

    What does that mean?

    Absolute pressure is relative to 0 psi - an absolute vacuum. You are correct - atmospheric pressure is about 14psi, depending on altitude. That's about what you should see on the scangauge with the key on, but the engine not running.

    When the engine is running under NOT under boost, it typically runs under a vacuum Remember those things called "vacuum hoses" on the engine? They're connected to the engine which is SUCKING in air most of the time. This means that the intake manifold is seeing less than atmospheric pressure - sometimes as much as 10 or 11 psi below atmospheric.

    What most of us consider boost is the psi ABOVE atmospheric that is going into the engine. When displaying MAP, this is reflected as atmospheric + boost - so 10 psi boost would be about 24psi MAP.

    Here's info on how to set the scangauge to display Boost.

    MINI COOPER :: North American Motoring - Electrical :: Displaying Boost on a ScanGaugeII
     
  3. Ofioliti

    Ofioliti New Member

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    Thanks, Blimey. Just the one I was hoping to reply. :D
    Sorry, yes , absolute, not atmospheric. (I had two glasses of wine with lunch:crazy:)

    OK, that makes sense now!

    So, just as a follow up... since it shoots up to around 21-22 psi, am I getting "good" boost (+8 psi above atmospheric)? I have the stock pulley.
     
  4. BlimeyCabrio

    BlimeyCabrio Oscar Goldman of MINIs
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    You should be making 10-11ish PSI boost peak.

    If you're only making 8, you may have a weak or poorly adjusted bypass valve... or a boost leak...
     
  5. Ofioliti

    Ofioliti New Member

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    OK. The +8 or so is not yet with the pedal full mashed :lol: Gotta peek a look at the gauge again when I'm flooring it and its safe.

    (And just to be sure... it should be +10-11 with the stock pulley?)
     
  6. BlimeyCabrio

    BlimeyCabrio Oscar Goldman of MINIs
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    Yep - there about. I get 14-15psi with a 15%
     
  7. Ofioliti

    Ofioliti New Member

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    OK, thanks again. :cornut:
     
  8. BThayer23

    BThayer23 Well-Known Member

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    Yup, I get 10.0 psi with a stock pulley, and you have to be wide open throttle, foot to the floor, and up over 4000(ish) rpm to hit max boost.
     
  9. Jason Montague

    Jason Montague New Member
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    Sounds like you guys have supercoopers(R53) rather than turbocoopers(R56). Mini Margi is an R56 MCS JCW and @ idle MAP=6-7, 70mph=12.8, 3rd gear/5000rpm/pedal to the floor=30 MAP(overboost). This rapidly comes back down when shifting gears and again usually hovers around 12-13 when maintaining steady speed.:Thumbsup: Jason
     
  10. BlimeyCabrio

    BlimeyCabrio Oscar Goldman of MINIs
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    Yep - we've been discussing supercharged cars - and have been talking about both MAP and boost numbers.

    So when you're seeing 12-13 MAP - the car is still running under vacuum. At 30 MAP, you're making about he same boost I do with my 15% pulley under the same conditions.
     
  11. Ofioliti

    Ofioliti New Member

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    Things are alright. I easily hit 25 psi (+11 psi boost) going up an incline without flooring it. :D
     
  12. Ofioliti

    Ofioliti New Member

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    What is overboost? :confused5:
     
  13. Nathan

    Nathan Founder

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    Overboost is an odd beast ...

    If in the normal course of tooling around town you encounter a situation where you floor it NOW for a time of up to 15 seconds the ECU will allow boost from the turbo to add another 3lbs (I think, correct me if wrong) of boost.

    This increase in HP and Torque will whisk you out of the situation quicker.
     
  14. Jason Montague

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    :Thumbsup: Thanks Paul and Nathan. Jason
     
  15. Ofioliti

    Ofioliti New Member

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    So the turbo actually generates 'excess' boost that normally is not used by the engine?
     
  16. Nathan

    Nathan Founder

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    I did a lot of searching on this and am coming up with very little info.

    From what I can piece together...

    It is programmatic, handled by the ECU. For a set period of time, said to be in the range of 7 - 15 seconds depending on where you read the turbo is allowed to spool to a greater RPM.

    Now my own thought is this would be controlled by some sort of blow-off type valve that is electronically controlled to stay closed or bleed off less boost then under normal circumstances.

    Then again, I could be completely wrong...
     
  17. Deviant

    Deviant Banned

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    I believe the ECU actually keeps the wastegate closed longer, allowing for more boost. Typically the wastegate is the device the controls the amount of exhaust flowing through the turbos. Devices like boost controllers adjust the amount of vacuum/boost going to the wastegate so that it opens at a higher level of boost than the internal spring itself would allow. The blow-off or compressor bypass valve is mostly for preventing the shock wave of a rapidly closing throttle from going to the compressor wheel, creating a stall which results in increased lag between shifts.
     
  18. Metalman

    Metalman Well-Known Member
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    I hope I'm not going off topic, and I apologize in advance.
    I've been wondering about the differences between a wastegate (which I think is inside the hot side of the turbo..... correct?) and a BOV (which is normally mounted on the cold side...... correct?). The MINI R56 S comes standard with the wastegate valve built inside the turbo... correct? Are the benefits of a BOV to reduce or eliminate a shock wave from damaging the turbo impeller? By bleeding off the pressure, it also allows the turbo to continue to spin at a high RPM so the pressure can build quickly, say during a transmission shift?
     
  19. lotsie

    lotsie Club Coordinator

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    Maybe we need a "How does a turbo work" thread.

    Mark
     
  20. Metalman

    Metalman Well-Known Member
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    Good suggestion:smile5:
     

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