6nz"d BXS Acert thumping noise

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by w9l, Jun 29, 2020.

  1. Brettj3876

    Brettj3876 Road Train Member

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    1st hand experience messing around with timing. Slightly retarded timing will pull way better than advanced timing.

    Pulling timing away will decrease hp but adds torque and boost. Your egt will run a bit higher but that's better than having excessive cyl pressures.

    Adding timing will see an increase in overall HP but torque will actually decrease torque and will lose rpms quicker on a pull. And if your running with bumped up timing do not lug it.
     
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  3. Brettj3876

    Brettj3876 Road Train Member

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    Your gonna be pulling it apart again with those 18: 1 packs and that tune.
     
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  4. Shawn2130

    Shawn2130 Heavy Load Member

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    Brettj3876: I hope not. There’s a few things I’d like to try that I’ve applied to other engines I’ve worked on when I want to make more power on.

    The tune itself wasn’t the reason for the head cracking which is why I’ve taken it apart.

    Besides, I’m always hearing stories as well of people going single turbo and still taking their engines apart.
     
  5. w9l

    w9l Medium Load Member

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    One thing I don't understand is how a basically stock Acert with compounds can make well over 40psi boost with no ill effects and at 18:1. But put a single on it and at 40psi you are gonna have a wreck. It already had excessive blowby before it was singled. I now think the guy that singled it knew it would let go so he could inframe it. Does have 6nz head now and industrial cyl packs. I don't remember what the cr is on those.
     
  6. Shawn2130

    Shawn2130 Heavy Load Member

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    The ACERT engine runs on the Miller operation cycle.

    That’s why they use Intake Valve Actuation.

    The IVA makes the intake valves stay open just a little longer which forces some pressurized air to go backwards into the intake during the compression stroke. This makes the engine more like a 16 to 1 compression engine for example.

    This is Cat’s way of making EGR work without the egr cooler. It’s supposed to make the engine be 15% more efficient while being cleaner.

    The high compression compensates for some of the charge being forced back into the intake.

    The small turbo prevents the intake charge from going too far by pushing back.
     
    Last edited: Jul 2, 2020
    Reason for edit: More info
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  7. Shawn2130

    Shawn2130 Heavy Load Member

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    If I remember right, the low compression packs are around 15:1.

    The 2 Pete’s we have with the 3406b’s are 16:1 and 16.7:1.

    So when someone re tunes the computer, turn off the IVA’s, the cylinders are now taking the full force of 18 to 1 compression along with the boost pressures of 40 plus psi of the two turbos or the single.

    I think my ACERT is pushing around 45-50 psi with the twins. The boost gauge says 60 but I’m not sure if that’s accurate.
     
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  8. Brettj3876

    Brettj3876 Road Train Member

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    I bet they pull some timing out to compensate for higher comp? @Superhauler the guy to ask
     
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  9. Superhauler

    Superhauler TEACHER OF MEN

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    More than likely when it was a twin turbo the vva's bleeded off the excess cylinder pressure even though it showed better than 40psi on the gauge. Because of the high comp pistons. Now when it was singled the vva's were removed or deleted so they couldn't "bleed off" the excess cylinder pressure. Which causes higher cylinder pressure with the single and high comp pistons. Its not "if" the headgasket will fail. Its "when" it will fail. Either cut the bowel of the pistons or install the low comp pistons.
     
  10. w9l

    w9l Medium Load Member

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    It now has the low compression pistons. BW 1496988 blows about 40psi. That turbo is supposed to support 750hp. I am not close so how did over speed it and break shaft? I notice boost gauge needle bouncing 2 or 3 psi when in a pull. Seemed to correspond with thumping. My thoughts were if one cylinder is hitting harder than the other 5 it would be likened to 5 ping pong balls hitting the drive side of turbo followed by a baseball on the 6th? Hammer the turbo to catastrophic failure?
     
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  11. swaan

    swaan Road Train Member

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    Shafts break from compressor surge. Not overspeed. Barking the turbo . Lifting off the fuel pedal too fast under a heavy pull will do this sorta thing. You can't drive like a cowboy when your pushing some HP. Ease on/off the go pedal and the truck will thank you.
     
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