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Anybody else done the N75 mod?

Discussion in 'A4/S4 forum(B5 Chassis)' started by Oranoco, Mar 6, 2011.

  1. Oranoco
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    Oranoco Well-Known Member

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    [Mar 6, 2011]
    If anybody isn't aware:

    Remove N75 valve, turn screw in end 1/2 turn anti-clockwise (it's hard to shift) and refit

    I had a spare one so thouht I would try it out. Definately seems to make the boost come in with more of a punch and it also seems to hold the boost further along the rev range before tailing off.

    Wondering if anybody else has done it and how they've found the effects?
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  3. Broken Byzan
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    Broken Byzan Photographic Moderator Staff Member Moderator VCDS Map User

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    [Mar 6, 2011]
    It;s the approx equiv of changing to a differebt boost control vavle, H, J etc.

    I tried it once but couldn't shift the screw and gave up,lol
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  4. Oranoco
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    Oranoco Well-Known Member

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    [Mar 6, 2011]
    lol, know what you mean mate if it had been the main valve I wouldn't have wanted to give it that much welly to the screw in case it broke
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  5. EdgeyA4
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    EdgeyA4 Member

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    [Mar 6, 2011]
    How do you remove the N75 valve? as i belive im having issues with mine (110 TDi AFN), with Boost trailing off at 2K etc
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  6. bengal
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    bengal Member

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    [Mar 6, 2011]
    I did it a while ago and it does work but I kept messing with it and ended up breaking it :keule:.
    I haven't touched the new valve since.

    There is a guide somewhere on the net which tells you which way gives more boost or less boost I'll see if I can find it.

    It's not really a guide but it does explain how it works and how to do it.

    What the N75 valve does... - SEAT Cupra.net - SEAT Forum
    Last edited: Mar 6, 2011
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  7. bengal
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    bengal Member

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    [Mar 6, 2011]
    The way I did it presuming it's the same on yours is, remove the top hose which goes to the actuator and drive it like that but don't give it full throttle as you will risk blowing the turbo or worse the engine, I capped my n75 when I did mine as it seemed better this way but try it without first.
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  8. Oranoco
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    Oranoco Well-Known Member

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    [Mar 6, 2011]
    I have no idea as to the effect of this on a diesel engine .
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  9. EdgeyA4
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    EdgeyA4 Member

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    [Mar 6, 2011]
    Thanks for the Advice, What do you mean by you capped your N75?, i did try taking the hose off my actuator earlier, i just tapped the accelerator at a stand still and boost gauge didnt move? so i dont no if you actually have to drive it?

    So if i get full boost with this pipe off the actuator it means i need a new N75? Sorry for all the Questions

    Thanks in advance
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  10. bengal
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    bengal Member

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    [Mar 6, 2011]
    Sorry I should have been more specific, basically I used a bit of pipe with a bolt wedged in so it's air tight and put that in place of the actuator pipe but tbh I don't think this is necessary. Presuming a diesel works in the same way as the petrols what it means is either the N75 or the wastegate if the boost is better if not it's something else. You do need to drive it but like I said take it easy but as the problem is noticeable at low revs you should be able to tell if there is a difference.

    You could try driving the car with the N75 unplugged as I have done this to pinpoint a bad N75 before on my 1.8T. Also you need to find out what pressure the wastegate opens at on a diesel, I know on a petrol it is about 5 psi, you can test the opening pressure by using an air pump on the actuator hose and see what pressure it opens at, normally it can be adjusted if it is opening too early. Having said that VCDS should help you out with the N75 as they normally throw a fault code when they go bad.
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  11. Oranoco
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    Oranoco Well-Known Member

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    [Mar 6, 2011]
    Absolutely do not drive with the actuator pipe off. You will lunch something expensive as it's pressure getting to the actuator that causes it to open and maintain a safe boost pressure. All pipes need to be present and correct. Modifying the N75 valve just alters the way it behaves not increasing the boost
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  12. bengal
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    bengal Member

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    [Mar 6, 2011]
    I agree with what you said about the actuator, I shouldn't really give advice like that although I have done it myself but only drove with part throttle it was for troubleshooting purposes. As for the N75 screw I wouldn't know about it not giving more boost as I don't have a boost gauge, it felt like it was boosting more to me but as you have said it behaves differently, I think it's more the boost coming on earlier and stronger but the peak boost is the same.
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  13. EdgeyA4
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    EdgeyA4 Member

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    [Mar 6, 2011]
    Well i tried driving the car (Just across a car park) without pipe off the top of the Actuator (before i saw the post about not to lol) but there was No boost What so ever? so does that mean i can Rule out the N75?

    At this moment in time i guess i will Double and Triple Check for boost leaks, ill take all the pipes off and check them, make sure there tight etc, as this seems to be the 1st, easiest and cheapest place to start at,

    If i can get the N75 off i will try adjusting the screw just to see if it helps abit, is the N75 easy to get off the car?

    Thanks Again
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  14. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Mar 6, 2011]
    Edgey: the actuator on a 110 TDI is vacuum actuated, so it wont act the same as a petrol engine.
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  15. EdgeyA4
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    EdgeyA4 Member

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    [Mar 6, 2011]
    Hmmm, This is getting confusing lol, Can i still adjust the N75 or test it any other way?
    #14
  16. bengal
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    bengal Member

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    [Mar 7, 2011]
    My advice for the adjustment is to leave it, only do it when the car is running okay plus if the N75 valve is dead then adjusting it won't do anything. See this is the thing with diesels, they work differently and I'm used to petrols lol.
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  17. tazzy baby
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    tazzy baby Rookie

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    [Mar 8, 2011]
    Mine is dead so im getting a new one this week so will hav a go at this,,, thanks for the tip Oranoco,, will let you know how it turns out
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