Stage 1 Switch Pitch

Discussion in 'The "Juice Box"' started by BA, Jan 26, 2014.

  1. 71GSX455-4SPD

    71GSX455-4SPD Nick Serwo Magic Car


    This going into a '72 Riviera with a Jim W. Built short block (forged pistons, 288-94h cam IIRC) topped with ported TA SE heads, an SP1 intake, 3.42 rear. I have a nice cruiser Buick, I'm looking for this one to be a bit more of a brute. Mostly street driven, but plan to race it at a few events a year. Definitely want it to get out of the hole (heavy car!) and have good top end. That idea is what started down the road of the switch pitch.

    Given that, does that give you some ideas on timer suggestions?

  2. gsgtx

    gsgtx Silver Level contributor

    is it true the converter goes back to low stall at about 4000 rpms, even at wide open throttle from the factory. thanks.

    BRUCE ROE Well-Known Member

    Torque converters multiply torque something like 2:1 at stall, a little bit more for a switch
    pitch. As rpm increases, the multiplication gradually goes to a straight 1:1. The stator that
    redirects fluid starts to freewheel in the other direction at that point. In effect it gives you
    an extra 2:1 gear set.

    Since I don't race cars, I let others tell me what electronic function they need. Email me at if you like. Bruce Roe
  4. 71GSX455-4SPD

    71GSX455-4SPD Nick Serwo Magic Car

    Hi Jim,

    Checking in for an update. The Riviera where this converter will be installed is targeted for road duty this year. Also, the trans cooling lines would be need as well.


  5. Jim Weise

    Jim Weise 1000+HP

    Will be on the way this week Ken. Your cooler lines were 1/2 NPT .. correct?

  6. 71GSX455-4SPD

    71GSX455-4SPD Nick Serwo Magic Car

    Correct, 1/2" NPT, thanks.
  7. bigtorque5

    bigtorque5 Well-Known Member

    the convertor goes to 1to1 when vortex flow reverses in side the converter
  8. Yardley

    Yardley Club Jackass

    Jim, they are like the ones you sold me. Same as the GS only longer and the ends were not installed. Ken will have to install all 4 ends after he runs the lines.
  9. Jim Weise

    Jim Weise 1000+HP

    Ya Yards.. just making sure I had ordered the right size fittings for his external cooler.

  10. jamyers

    jamyers 2 gallons of fun

    What's the GM part # for the orifice plug, and what size to drill it? I've looked but apparently my "search-fu" is weak tonite.
  11. Jim Weise

    Jim Weise 1000+HP

    GM part number 8628864

    125, 125C, 3T40 orifice plug for servo in the case is what works.

    It's .255 in diameter and you drill a hole in it with a #60 drill bit.

    The trade p/n is D64484A

    Most online trans parts outfits stock it.

    price varies between 6 and 10 dollars.

    Good luck

  12. jamyers

    jamyers 2 gallons of fun

    Thanks! I'm seeing it online being called a servo air bleed, a transmission vent cap, and (most accurately) a Cup Plug Orifice.
    To refresh my memory, this restricts the fluid coming out of the converter when it is in high stall?

    BRUCE ROE Well-Known Member

    I have a bunch of 12" & 13" switch pitch converters needing rebuilding, can you send me your
    email so we can arrange details? thanks, Bruce Roe
  14. Jim Weise

    Jim Weise 1000+HP

  15. bobc455

    bobc455 Well-Known Member

    Sorry to hijack the thread.

    What are the consequences if the case plug is not drilled, or drilled with an incorrect size?

    I'm trying to diagnose a switch-pitch that doesn't seem to be switching correctly. (It reverts to low-stall under heavy throttle, even when it's supposed to be in high-stall)


    -Bob C.
  16. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    That may be normal, I'm not sure. I think I read somewhere that above a certain RPM, fluid flow in the converter forces the stator blades back to low stall. Maybe JW knows for sure?
  17. Jim Weise

    Jim Weise 1000+HP


    That is most likely caused by a leak in the activation system... the most likely cause is worn out stator bushings, or a damaged sealing surface on the stator shaft. Other concern areas are the piston/ring in the converter stator, or the cast iron sealing ring on the input shaft, and related surfaces.

    If it goes into high stall, the orifice plug is there, and the hole size is in the ballpark.

    No, it's not normal, the stator fins are moved by hyd pressure, and the highest force would actually be during initial launch, as it would be attempting to re-direct the most fluid under those condtions. Stator fins will stay in the high stall position as long as the solenoid is energized.

    What Larry is talking about is this.. as pump and turbine speeds nearly equal each other near coupling speed, the stator becomes ineffective, so what position the blades are in becomes less of a factor in converter operation.

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