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Thread: Boost Pressure higher than estimated - causes?

  1. #1
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    Boost Pressure higher than estimated - causes?

    Would like input on why my boost pressure is so much higher than estimated by this worksheet.

    Made the following mods to stock '02 HD, 58K miles:

    Replaced cat back with Magnaflow
    R&R Supercharger - cleaned intercooler, replaced gaskets, TTY bolts, closed off lower PCV
    Replaced stock plugs with NGKTR6 gapped to 0.32"
    Replaced stock LP with Metco 9.5" (8lb)
    Replaced stock TB with single blade SCT
    Replaced stock CAI with JLP
    Added Mafia to MAF
    Added oil separator
    Pro Dyno Tune yielding 433.2 RWHP and 569.3 ft lbs of torque

    Tuner said the engine is making a lot of boost - it pegs my Autotune gauge just above 3K (15lbs) and tuner said it is making 19lbs above 5K. That seems high when compared to the calculator referenced above, which says I should be seeing 12.5lbs.

    Tuner said my cats got a little stinky as he was tuning - thinks maybe I would benefit from a freer flowing exhaust system, but doesn't think my boost pressure would drop.
    Is maybe the combo of JLP CAI and SCT TB reducing the inlet tract pressure drop? If I lower this value in the worksheet to 0.5psi from 1psi the calculated boost goes up to 15.
    I would question the gauge except the tuner put his own gauge on and it matched.



    Other thoughts? Crankcase ventilation imminent, or safe to play (I'll keep it below 5K)?

  2. #2
    Mobbin around the NW
    Name: Derek

    SonicHD's Avatar
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    I'd say with those mods, you should be about 12-14lbs boost max. I dont see how on Earth you could see 19lbs with those mods. Since boost is a measure of resistance, you must have a blockage somewhere? You're sure it still has the stock upper pulley, right? The power numbers are solid, though a little high for the mods mentioned, especially the torque.

  3. #3
    Registered User
    Name: Derek


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    Thanks for the feedback, SonicHD. Will advise if I get it sorted. Here's a pic of the tq/hp printout.

    20170411_145309.jpg

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