OMG I need desperate MBC help!!!

  • #1

    OMG I need desperate MBC help!!!

    ok this is my second mbc (the first one was a cheapo ebay) the new one is a hallman pro rx. i took the "j" hose off and replaced it with about a foot of hose with the controller in the middle. whenever i test it with the mbc needle turned all the way to 0 i get 5 lbs of boost, then when i turn it up gradually i get 5lbs of boost no matter what i do i get 5lbs of boost!!! when i connect the hoses without the mbc i go back to 6lbs with no leaks. WTF is going on >?>!!!?!>!>!@#<

    1986 300zx turbo
    1999 Buick Park Ave Ultra *Ported supercharger, smaller pulley, intake, 3"exhaust manifolds (my fast grocery-getter)
  • #2
    pretty sure it's the pop off valve.

    it's SUPPOSE to bleed air at 10 psi but the spring gets worn and week and usually it opens alot sooner 5 - 7 psi

    he gives me shit all the time about the money i spend on my car but he simply doenst understand what type of "high" you get from watching a stock car transform into something alive with as much emotion and feelings as any human.
    Originally posted by PurePontiacKid
    My god… 10 pages and so far he's only pulled the motor out of the donor car, and bought some valvetrain parts for it? way to be proactive guys.
  • #3
    i see , obviosly this would be dangerous because the turbo may over spool and EXPLODE, bust can i just use a cap npt cap to block it off?

    1986 300zx turbo
    1999 Buick Park Ave Ultra *Ported supercharger, smaller pulley, intake, 3"exhaust manifolds (my fast grocery-getter)
  • #4
    nutball wrote: i see , obviosly this would be dangerous because the turbo may over spool and EXPLODE, bust can i just use a cap npt cap to block it off?
    take the pop off valve off and go to a plumbing place thats sells parts or home deport and they should have the size.

    OR just get a N/A intake plenum

    i wouldn't spool over 12psi though.

    he gives me shit all the time about the money i spend on my car but he simply doenst understand what type of "high" you get from watching a stock car transform into something alive with as much emotion and feelings as any human.
    Originally posted by PurePontiacKid
    My god… 10 pages and so far he's only pulled the motor out of the donor car, and bought some valvetrain parts for it? way to be proactive guys.
  • #5
    Re: OMG I need desperate MBC (and boost gauge) help!!!

    Thanks for the help!!!! :twisted: ALSO where is the best place to plumb a boost gauge mine is tee'd off of the main boost line, but i checked some old write ups that show it going to the intake manif, they removed a random bolt, but where the random bolt was on there car i have a bolt with a vacuum line coming out. where should i put it?!?! http://www.mys15.org/bobsharp/Tech/Z31/Boostgauge.htm thats the write up

    1986 300zx turbo
    1999 Buick Park Ave Ultra *Ported supercharger, smaller pulley, intake, 3"exhaust manifolds (my fast grocery-getter)
  • #6
    plug is 1" NPT.

    1988 300zxt. gt35, stance, etc. Wheels: Varrstoen ES2 18x9.5 et-13 225/40. 18x10.5 et0 245/40
    1990 jetta vr6'd
  • #7
    Um, I highly doubt it is the pop off valve causing you to only hit 5 psi of boost. Why would the pop off valve allow him to hit 6psi in stock form but then knock it down to 5 when he slaps the MBC on there? You probably have your boost controller hooked up wrong.
    Pull off the boost controller, look at it, play with it, touch it squeeze, hold it, love it and figure out how it works. Remember, you are trying to manipulate the signal to the waste gate actuator, essentially blocking air from getting to it.

    For your gauge placement. You should put it on your plenum, this way you know what the ENGINE is seeing, not what the pressure is at any other random point or pipe.
    85 Z31 6.0 LSX turbo 766whp/792wtq
    04 GTO, LS6, big cam, porting, N20… underway for summertime daily driver.
  • #8
    while you are getting the piece to block off the pop off grab all of the vacuum fittings as well. They come in handy.
  • #9
    SATAN wrote: Um, I highly doubt it is the pop off valve causing you to only hit 5 psi of boost. Why would the pop off valve allow him to hit 6psi in stock form but then knock it down to 5 when he slaps the MBC on there? You probably have your boost controller hooked up wrong.
    Pull off the boost controller, look at it, play with it, touch it squeeze, hold it, love it and figure out how it works. Remember, you are trying to manipulate the signal to the waste gate actuator, essentially blocking air from getting to it.

    For your gauge placement. You should put it on your plenum, this way you know what the ENGINE is seeing, not what the pressure is at any other random point or pipe.
    In my experiance when the boost controller is hooked up wrong you get infinite boost.. Happend to me before..


    If its a use MBC it might need a rebuild..
    1989 300ZX 2+2 N/A GLL
    Auto to Manual Swap
    NA2T Complete
  • #10
    i GOT IT!!! thanks for the help!, i found an empty block off bolt on the manifold for the gauge and my problem with the controller was that i was doing little 1/4 turns but to get it to 11lbs it took 5-6 full turns. :twisted: crazy what a difference it makes

    1986 300zx turbo
    1999 Buick Park Ave Ultra *Ported supercharger, smaller pulley, intake, 3"exhaust manifolds (my fast grocery-getter)