1JZ Overboost Issue! Modded Soarer. Please Help.

Thread in 'Technical Questions' started by Zee, Jun 15, 2023.

  1. Zee

    Zee New Member

    Jun 15, 2023
    Likes Received:
    Hi everybody. Im new here, I live in japan so greetings to everybody. I just bought a soarer single turbo factory manual. It has over boost issue.
    Let me write down the mods so you guys know what it is.
    Mod List
    HKS front mount intercooler
    HKS air cleaner
    Aluminium Piping
    Aftermarket Blow off valve (wastegater)
    Aftermarket Exhaust manifold
    After market Dual Exhaust
    KOYO Radiator
    HPI Radiator Hose
    GP Sports Radiator Fan
    Ogura Twin Plate Clutch
    Front Tower Bar
    Aragosta Coilovers
    Shuttle Works Knuckles
    Tomei 2WAY LSD
    Aftermarket Steering
    APEXi Boost Guage
    Defi Water Temp Guage
    GReddy PRofec-B Boost Controllee
    HKS Turbo Timer
    Stock Turbo btw.

    Thats probably it for the engine suspension mods as far as I remember.

    When I got the car, it was fully straight piped from cat till rear end. And for some reason the boost will spike to 1.3 around 3rd 4th and 5th gear or maybe 2nd too, Im not quite sure. Now I know after reading a couple forums that the non-restricted straight pipe flow should cause boost spike no matter what. But the thing is, previous owner told me that he was running 1.05 bar and it didnt overshoot and he is a pro drifter, he drifted it a couple times a month and maintained it like a baby, its 120K km and not a single drop of oil that leaks for anywhere. All the head gasket and timing belt and water pump stuff has been replaced and well taken care of from time to time.
    I just dont know how he ran 1.05 with stock ECU without fuel cut or maybe he never tried slamming the accelerator pedal in a straight line on 3rd 4th and 5th gear. He owned the car for 6 years and he is a mechanic so Im pretty sure he knows what he is talking about.
    Now I just bought a dual exhaust with four mufflers/resonators and put it on the car to pass the inspection, returning it to its stock condition for a day And I haven't driven the car yet to the point I could test the overshoot issue but it def felt the boost build-up became sloppy and slow after putting the exhaust on. But please help and tell me is there anyway the boost will be controlled to 1.05 with full straight piped 1jz? like the previous owner said? Is anything wrong with the car? Should it spike or is something wrong? and what should I do to fix it cause Im planning to change the exhaust to something lighter and single instead of dual with only one resonator and de-cat after I pass the inspection so the flow will be better and it will def spike again. Any help would be appreciated. Thank you so much im advance!

  2. Japtorque

    Japtorque Active Member

    Oct 25, 2018
    Likes Received:
    put a 50mm restrictor in the exhaust and see if it fixes the overboost
  3. Zee

    Zee New Member

    Jun 15, 2023
    Likes Received:
    2A13D5FF-840E-4C4E-A587-9B0B2066AD33. I put this exhaust on and now the boost is around 0.7 0.8. But the problem is now if I try to increase the boost on boost controller, it doesnt go up. I was thinking maybe around 1 bar but it just stays till 0.7.

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