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Thread: JB4, Auto Trans, Boost - logs show boost holds

  1. #1
    Join Date
    May 2017
    Location
    Ontario, Canada
    Posts
    512
    My Cars
    335i E93 N54

    JB4, Auto Trans, Boost - logs show boost holds

    Hi all,

    My friend has a Manual Trans and you hear his boost drop in his BOV when shifting.

    My car is Auto Trans and looking at the logs and feel, there is no boost drop when shifting (I paddle shift around 6000-6500).
    My car does this in map 0 as well, so not sure it's JB4 related.

    Can I have your thoughts on this?
    I thought there was a JB4 feature that held boost... though not sure if that is strictly for manual or auto.

    My JB4 is used, so it's conceivable that it's not at default settings (though I looked at all on phone via BT and don't see this option)

    Thanks.
    Last edited by Codes2; 01-14-2018 at 01:38 PM.

  2. #2
    Join Date
    Dec 2012
    Location
    North Carolina
    Posts
    1,450
    My Cars
    2009 335i M-Sport Coupe
    Auto cars hold boost, manual cars dump boost when you shift. Since you lift off the throttle to shift a manual, the throttle closes and the car dumps boost. You can technically add a feature called "no lift shift" where the car aggressively cuts timing when you clutch in, so you can shift without letting up on the throttle. NLS can be really hard on the turbos and cats, so I wouldn't recommend it. Because of the timing cuts, you shoot burning fuel into the turbos and cats, which can dramatically shorten their life. Things like 2-step, no lift shift, and burble tunes tear up turbos and melt cats.

  3. #3
    Join Date
    May 2017
    Location
    Ontario, Canada
    Posts
    512
    My Cars
    335i E93 N54
    Thanks RS.

  4. #4
    Join Date
    May 2017
    Location
    Ontario, Canada
    Posts
    512
    My Cars
    335i E93 N54
    I casually wonder if this is why the auto is widely considered to be slightly faster. Not so much the trans, but rather due to boost.

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