MAF vs. MAP - Turboing an NA Car

Discussion in 'OT Driven' started by Kroze, Feb 22, 2008.

  1. Kroze

    Kroze Active Member

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    What?
    I'm a noob at this and wanted some insight. If you were to turbo an Non-Turbo car that's using MAF system, will you have stalling issues since it doesn't compensate for elevation & temperature differences? How can you fix this?

    I read this from another forum and got confused.

    Piggyback fuel unit. It poses problems such as having to manually compensate for temperature, and altitude changes. I for one went the standalone route with my MAS based car and had a local SoCal tuner take care of that. On my MAP based turbo car, it was tuned with a SFMU, EGT, and Wideband. To this day it makes good/usable power without any issues, or having to constantly fidgit with fuel pressure or rise rate.
     
  2. Kenny Powers

    Kenny Powers OT Supporter

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    TRUMP IS MY PRESIDENT
    wat?

    not that i've done it, but i can't see why you'd have stalling issues
     
  3. Bugalu

    Bugalu OT Supporter

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    the ecu has sensors for temperature and elevation, so the car will automaticaly correct for these.

    put the maf before the turbo and make sure you arnt maxing it out, get it tuned, and you will be good to go.
     
  4. alltracman78

    alltracman78 New Member

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    The piggyback intercepts some of these signals and modifies them.
    If you get rid of the MAF [you're probably going to max it out anyways] and use a MAP sensor you'll need to add a intake temp sensor [most times the intake temp is part of the MAF sensor].
    The PCM should still be able to read elevation however, it's normally not measured via the MAF sensor.
    You can't run a nonturbo car with a turbo without adding some kind of piggyback or stand alone to manage the extra fuel, it's normally more than the stock PCM can handle.

    What engine/car is it?
     
  5. Bugalu

    Bugalu OT Supporter

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    you also need a convertor to conver the map signal to what the factory computor is designed for. if you have a popular application this part might be readily availible. if not....

    well.
     
  6. alltracman78

    alltracman78 New Member

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    Hence the piggyback.
    Something like an HKS VPC [old school] or a MAP ECU.
     
  7. Bodhi

    Bodhi My crotch is red .. my lambos blue .. and ill be g

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    yup .. or for the do-it-yourselfer .. ive seen some mega-squirt setups that have done decently in terms of a properly running idle/cold start/etc ..

    .. speed density or map setup .. MAF's blow when converting an N/A setup from the factory to forced induction .. even with most nitrous setups (dry shots) ..
     
  8. deusexaethera

    deusexaethera OT Supporter

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    My car has a turbo. The MAF is before the turbo, the air temperature sensor is after the intercooler, and there is no air pressure sensor because it's the amount of air that matters when metering fuel, not the pressure.

    (of course, the fuel rail does have a pressure regulator capable of dealing with up to 25psi above ambient air pressure.)
     
  9. Mr3GTP

    Mr3GTP OT Supporter

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    O motherfucking HI-O
    The main problem I encountered with forced induction on a speed-density system (EECIV, lol) was idle surging. Why this happened at idle (with boost at zero) i don't know. I simply unplugged the idle air control and set the idle manually. I also unhooked the EGR. Kinda ghetto (no, VERY ghetto), but I've run it over 10,000 miles like that, so it works OK. Idles good once warm, and is turn-key reliable. I do occasionally have to fuck with the fuel pressure, but for the most part I just thrash on it.

    A real control system (and a serious tune) would get a lot more out of my boosted shitbox, but I have other priorities for the funds right now. :mamoru:

    I'll save that expense for when I'm running more than 7.5 pounds. :x:

    Besides, it's a toy, not my life's work...
     
  10. alltracman78

    alltracman78 New Member

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    Idle surge on MAP sensored engines usually means a vacuum leak.
    Did you check for one at all?
    Are you using the stock MAP sensor?
    If so, I assume it doesn't read positive pressure?

    Welcome to speed density, AKA MAP sensored engines.
    They don't use airflow, they use manifold pressure and RPMs to determine fueling.
     
  11. Mr3GTP

    Mr3GTP OT Supporter

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    Yes, I checked for vac leaks, found none. MAP sensor is stock. The only changes made to the engine controls are;

    PCV eliminated

    Idle Speed Control disabled

    EGR disconnected (header has no provision anyway)

    MSD Boost Timing Master

    Kirban adjustable FPR

    Bigger injectors

    Walbro pump.

    I had to move the battery, build an airbox, etc, but those changes were just to make room for the blower, FMIC, and cold-air box. The fucker runs pretty good for a ghetto build; I know it can run better, and I'm making the necessary changes as the cash becomes available...
     
  12. deusexaethera

    deusexaethera OT Supporter

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    Yeah, I know what it is. My old Mazda had a MAP sensor. If the guy has the option to use a MAF instead, depending on how invasive his upgrade is going to be, then he'd be better off using one instead of a MAP. MAFs are more accurate because they don't have to calculate anything -- the air mass is measured directly.

    On the other hand, if he's sticking with the stock MAP sensor (or a turbo-compatible direct replacement), then all of the sensors should be after the intercooler -- that's where they were on the Mazda MX-6 Turbo, according to my shop manual.
     
  13. Bugalu

    Bugalu OT Supporter

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    OFG.

    SHUT UP.
     

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