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Thread: Running rich with FMU?

  1. #1
    Junior SCH Member
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    Jul 2004
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    Running rich with FMU?

    My car is stock except for shorty headers, O/R H-pipe, flowmaster catback and underdrive pulleys. How rich will my car run with the FMU supplied with the blower and will it be to rich to run the car all spring summer and fall like that?

    Next winter i'm gonna ditch the FMU and run 36lb injectors and 75mm Pro M
    91 Mustang GT

    shift kit'd AOD, 3.73 gears, MAC shorty headers, O/R H-pipe, 40 series flowmasters"original", underdrive pulleys, BBK CAI, 16x7 BBK Speedware chrome pony wheels, Cervinis Cobra R Hood and new showroom quality paint

    Soon to come: Brand new interior, AOD to T5Z swap

  2. #2
    Junior SCH Member
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    Dec 2003
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    Montreal
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    Should be ok if you have the stock 19lbs. Better too rich then too lean. If you think your running too rich you can always recalibrate the FMU with a 10:1 disc instead of the 12:1 supplied with it for about 30-40$

    Simon

  3. #3
    SCH Moderator "SN Guru" speedytang's Avatar
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    FMU only works under boost so your usually ok. If it is to rich on WOT you can always change the disc or add a fish tank valve in the vacuum line of the FMU to adjust its action.

  4. #4
    Junior SCH Member
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    Quote Originally Posted by speedytang View Post
    FMU only works under boost so your usually ok. If it is to rich on WOT you can always change the disc or add a fish tank valve in the vacuum line of the FMU to adjust its action.
    Can you elaborate on this?
    92 GT w/373,T-5, 70mm TB, 75mm MAF,MM LCA's/FRP UCA, BBK 1 5/8 headers, MAC H-pipe, FMS aluminum D/S, 3G, MSD6AL, BTM, Thumper ported GT40s, Cobra intake w/TMoss ported lower, Crane 2031, Crane 1.7 rockers, 42lb injectors, CF DF, Novi 1K, 8" lower, UPR PP, AIS
    432/407 RWHP/RWTQ @11lbs SCT tuned

  5. #5
    SCH Moderator "SN Guru" speedytang's Avatar
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    If your to rich under WOT you can cut the boost back to the FMU by using adjustable air valve like used with a aquarium. The Super FMU by Vortech used this technique except it was manufactured into the top of the unit at the vacuum nipple. For those that did not have the money for new injectors and used a FMU I have always used this method instead of replacing the disc unless the A/F was just so far off that the lower disc was the only solution. Tuned Turbo cars like this also back in the 80's when no other solution was made yet. The best solution is always matching the injector size to the car output.

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