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Thread: Boost question

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    Boost question

    I have been trying to figure out something and need some help/advice.

    This is all based on 3rd gear logs same map, same road, same day, same song on the radio;

    So if i start the run in the 2.5k - 3k rpm range, a lot of taper and boost loss at 5.5krpm to 6k.
    However if i start the run in 2nd gear, then shift to 3rd, (rpm falls just above 4k) i then hold the boost perfectly to 6k.
    Difference between them is 2 psi, (11psi on the former and 13psi on the latter at 6k).

    This question might be related to different air flow at different RPMs or the rpm the turbos are spooling, but i do remember 14 years ago i failed all classes in science (physics, biology and chemistry) so let me know your thoughts please

    Thanks

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    Which tune and what mods?

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    Cobb s2 aggressive all bolts no FMIC (which is being installed as we speak)

    335i e92 AT 2007

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    Click here to enlarge Originally Posted by Bash Click here to enlarge
    I have been trying to figure out something and need some help/advice.

    This is all based on 3rd gear logs same map, same road, same day, same song on the radio;

    So if i start the run in the 2.5k - 3k rpm range, a lot of taper and boost loss at 5.5krpm to 6k.
    However if i start the run in 2nd gear, then shift to 3rd, (rpm falls just above 4k) i then hold the boost perfectly to 6k.
    Difference between them is 2 psi, (11psi on the former and 13psi on the latter at 6k).

    This question might be related to different air flow at different RPMs or the rpm the turbos are spooling, but i do remember 14 years ago i failed all classes in science (physics, biology and chemistry) so let me know your thoughts please

    Thanks
    You may have a vacuum leak which on a longer pull will not allow enough vacuum to accumulate in the tanks to be available for application to the wastegates (e.g. torn vacuum line going to/from the vacuum tanks, vacuum tank nipple broken, etc.)...it might also be weak wastegate solenoids...post up a datalog and we can have a look

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    Click here to enlarge Originally Posted by Bash Click here to enlarge
    I have been trying to figure out something and need some help/advice.

    This is all based on 3rd gear logs same map, same road, same day, same song on the radio;

    So if i start the run in the 2.5k - 3k rpm range, a lot of taper and boost loss at 5.5krpm to 6k.
    However if i start the run in 2nd gear, then shift to 3rd, (rpm falls just above 4k) i then hold the boost perfectly to 6k.
    Difference between them is 2 psi, (11psi on the former and 13psi on the latter at 6k).

    This question might be related to different air flow at different RPMs or the rpm the turbos are spooling, but i do remember 14 years ago i failed all classes in science (physics, biology and chemistry) so let me know your thoughts please

    Thanks
    isnt cobb load based?

    you need a vbox and the log to correlate to get accurate. just because you start "same" place isnt always true. load, IAT and im sure a few other parameters are changing that affect your boost

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    Click here to enlarge Originally Posted by LostMarine Click here to enlarge
    isnt cobb load based?

    you need a vbox and the log to correlate to get accurate. just because you start "same" place isnt always true. load, IAT and im sure a few other parameters are changing that affect your boost
    Thats a good point.

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    1 out of 1 members liked this post. Reputation: Yes | No
    I figured it out and as Dzenno mentioned i did have a leak. i came to notice when changing my FMIC that the cold side had some oil residue on the pipes, so figured that as the leak. When i changed the FMIC and tightened everything up i was seeing normal boost again with the higher map its crazy fast.

    Thanks to all that replied.

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