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Turbo Overboost

Austineer Nov 3, 2004

  1. Austineer

    Austineer King of cabs ;) Audi A3 Audi Cabriolet Owner Group TDi


    I interested if any of you guys have a boost gauge fitted and have notice your cars overboosting when accelerating hard in 4th & 5th gear at low rpm. My A4 has a sustained boost of 1.32-1.43 (20-21 psi) during hard acceleration in 1st 2nd and 3rd (without fluctuating), yet when I put my foot down in 5th doing 50 mph @ just over 2000 rpm the car boosts to 1.7 bar. When the car reaches about 80 mph ish with the revs @ about 3500 the boost then drops down to 1.32-1.43 bar and sustains that without fluctuation.

    When the car in running in the 1.7 bar zone it is like a complete limp snail and I guess the engine auto protection system kicks in. However i still dont know why the car is able to generate that much boost during those conditions when it controls the boost at all other gears/revs/speed. Any information or thoughts would be appreciated.

  2. AndyS3

    AndyS3 Member

    From memory Kim collins told me that the S3 has full boost on in 5th gear at about 1500 rpm so A4 is probably similar.
  3. Austineer

    Austineer King of cabs ;) Audi A3 Audi Cabriolet Owner Group TDi


    Thanx for that. Maybe it is a trate of the 1.8T to have full boost in 5th at low rpm. But It seems as though my boost setting is still too high compared to my other gears. For example with my car I could probably accept the 1.36-1.43 boost pressure in lower revs in 5th as the engine protection system wouldnt kick in, but 1.7 bar is way too high. So still cant figure out why there is differences though in the max boost pressure reading under different gears.
  4. t30gue

    t30gue Member

    Perhaps you need an overboost kit from www.boostvalve.com in the US. Look at their site.(think it's under 1.8t overboost solution or similar)It enables you to set the max boost your car can produce with a modified bleed valve. They are normally used if you are running a 1.8t with different N75 valve (gives higher peak boost)You can then set a boost ceiling just below the limp mode level, say 1.5 bar.
    All in with delivery the part is around £45 with excellent instructions.
  5. dickys3

    dickys3 Moderator Staff Member Moderator

    [ QUOTE ]
    welshdragon said:

    Thanx for the info. I think I will see what happens when I change the software first and if its still overboosting then that looks a good solution to try next. By they way where in south wales u from?

    [/ QUOTE ]

    Chris is from Neath.

  6. Austineer

    Austineer King of cabs ;) Audi A3 Audi Cabriolet Owner Group TDi


    I should be able to make it on saturday aslong as I can get away from the decorating. I did have a different N75J valve with the new turbo but I changed it back to the OEM one. The problem just reduced a little when I changed it back but it didnt actually go away. Will be speaking to superchips today to discuss my software update where the problem is most likely to lie.

    However as I meantioned in a previous forum I think this overboost problem have always been there but just seemed more noticable when modifying and in particular when I actually had the boost gauge (noting that this may not be 100 % accurate).

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