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Thread: Two Level Boost

  1. #51
    S15R Guest
    my mate had a Starlet GT, it was overboosting at high rpm and still cant find the problem but after he changed the turbo with external wastegate, no boost spikes anymore

    probably too much exhaust going out and small wastegate?

    try putting it on dyno again!

  2. #52
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    To much flow maybe
    You could try to put your cat in again to get some restriction in the exhaust.
    That would slow boost down abit. Perhaps enough to stop the spiking.

    If this is totally wrong feel free to flame me Just thinking out loud.
    Nissan GTR -09 Now with Cobb accessport stage 2

  3. #53
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    Boost creep, I'm told. Make the wastegate bigger or get an AVCR to control to boost at specific rpms...

    Tested it at lunchtime with the actuator disconnected and the wastegate tied open. Pulled 0.5 bar at peak. Should be 0...

  4. #54
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    So it could be a wastgate issue, what would cause it to open to early, or by the sounds of it, intermittently?

  5. #55
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    Quote Originally Posted by Nicely
    Boost creep, I'm told. Make the wastegate bigger or get an AVCR to control to boost at specific rpms...

    Tested it at lunchtime with the actuator disconnected and the wastegate tied open. Pulled 0.5 bar at peak. Should be 0...
    OK. So your turbo flows more air than the actuator is able to evacuate.
    If you was to fit the stock cat or turbo-elbow. Wouldn't that reduce the flow in the turbo and the actuator would do it's work properly again?
    Nissan GTR -09 Now with Cobb accessport stage 2

  6. #56
    yewei Guest
    nicely did u replace ur mani by urself? as in DIY? i'm having problems with my car, it sounded jus like a tractor n lost a lot of power. i think i got a cracked mani? could u guys give me some pointers? is the mani + dump pipe from ss auto-chrome or xs-power recommendable?? thanx for replying

  7. #57
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    Hey yewei. Sounds like its more likely the turbo to mani gasket. Regardless, you'll need to replace the gaskets when you take everything off to get to the mani. It'll be pretty obvious if the gasket's gone, as it'll have a section missing out of it

    I did it myself (with the help of a mate). If you would like a guide, take a look at this one

    I wouldn't recommend either of those manis The quality is rubbish. They tend to crack more easily and are very untidy inside. If you don't mind paying a bit more, get the Tomei one off Greenline

  8. #58
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    Looks as though its boost creep. Its taken a year, but I finally got a diagnosis off one of the SXOC Mods

    Disconnected the actuator arm from the turbo and tied the wastegate flap open. This should ensure that zero boost can build. Floored it in 5th and 6th over the usual peak power points where the problem usually occurs. Boost started building as the revs increased and peaks at 0.5 bar. With the wastegate fully open...

    This means that the wastegate isn't large enough to allow the boost pressure to escape quick enough to keep up with the flow of the exhaust.

    Three options:

    1. port the wastegate slightly larger. This is a documented and proved process.
    2. fit an external wastegate. Expensive and a ball ache.
    3. fit a smaller turbo elbow/dump pipe to increase the amount of back pressure and slow the flow.

    Now, Meddy had a near identical spec to me and never encountered boost creep. The only major difference in spec is that he still had the standard manifold. I've got to think about it, but I'm seriously considering fitting a standard main back on...

    To those with a tubular mani, you may well find you have the same problem once you try to boost over 1 bar if you have a T28BB...

  9. #59
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    Quote Originally Posted by Nicely
    Looks as though its boost creep. Its taken a year, but I finally got a diagnosis off one of the SXOC Mods

    Disconnected the actuator arm from the turbo and tied the wastegate flap open. This should ensure that zero boost can build. Floored it in 5th and 6th over the usual peak power points where the problem usually occurs. Boost started building as the revs increased and peaks at 0.5 bar. With the wastegate fully open...

    This means that the wastegate isn't large enough to allow the boost pressure to escape quick enough to keep up with the flow of the exhaust.

    Three options:

    1. port the wastegate slightly larger. This is a documented and proved process.
    2. fit an external wastegate. Expensive and a ball ache.
    3. fit a smaller turbo elbow/dump pipe to increase the amount of back pressure and slow the flow.

    Now, Meddy had a near identical spec to me and never encountered boost creep. The only major difference in spec is that he still had the standard manifold. I've got to think about it, but I'm seriously considering fitting a standard main back on...

    To those with a tubular mani, you may well find you have the same problem once you try to boost over 1 bar if you have a T28BB...
    I would fit the stock manifold.
    It's free

    Edit: What about fitting a racing cat?
    Nissan GTR -09 Now with Cobb accessport stage 2

  10. #60
    Meddy Guest
    Quote Originally Posted by Nicely
    Looks as though its boost creep. Its taken a year, but I finally got a diagnosis off one of the SXOC Mods

    Disconnected the actuator arm from the turbo and tied the wastegate flap open. This should ensure that zero boost can build. Floored it in 5th and 6th over the usual peak power points where the problem usually occurs. Boost started building as the revs increased and peaks at 0.5 bar. With the wastegate fully open...

    This means that the wastegate isn't large enough to allow the boost pressure to escape quick enough to keep up with the flow of the exhaust.

    Three options:

    1. port the wastegate slightly larger. This is a documented and proved process.
    2. fit an external wastegate. Expensive and a ball ache.
    3. fit a smaller turbo elbow/dump pipe to increase the amount of back pressure and slow the flow.

    Now, Meddy had a near identical spec to me and never encountered boost creep. The only major difference in spec is that he still had the standard manifold. I've got to think about it, but I'm seriously considering fitting a standard main back on...

    To those with a tubular mani, you may well find you have the same problem once you try to boost over 1 bar if you have a T28BB...
    Sorry but thats not correct mate. With the wastegate fully open it wont mean your not going to build any boost it just means the boost will be slower to build and will ultimately be a bit lower in level. The max exhaust flow a wastegate can bleed off is only about 30-35%.

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