Hi-Po verses normal TH-200-4R

From: Greg Moore (surfbeat at email.msn.com)
Subject: Transmissions

    Let me clear my throat....200-4R trannys were available
    in both SS's and garden variety Montes from 84 to 88.
    The hi-po versions have special codes on the ID tag.
    According to my reference article, many of the mods made
    to the hi-po 200-4Rs were performed on the valvebody,
    and all were done for the purpose of firming up the shifts.
       On these trannys, the MTV (modulated throttle valve)
    upshift spring was removed to give full line pressure at
    all times, and the 1-2 accumulator spring is stiffer than
    those used in milder car models. The TV's (throttle valve)
    boost valve diameter was increased to .474 (others were
    .326, .325 or .324). Pat Barrett of Level 10 says that this
    mod alone is akin to going from 7:1 compression to 14:1
    in an engine. Holes in the separator plate are larger than
    normal at approximately .074, again to firm up the shift.
       The servo on these trannys (hi-po) has a casting #
    on the outside. The GN and '89 Anniversary T/A end with
    94 while all other hi-po 200-4R's end with 92, and both
    are lipseal servos. The difference in these servos is that
    the 1-2 relief spring in the 94 servo is the strongest spring
    made that will fit in the housing. The 92 servo contains
    the second strongest spring.
       According to Barrett, many people think that the servo
    spring should be soft for a firm shift. This is a miscon-
    ception, it should be strong to allow more pressure to
    build up behind it before it releases to get a firmer shift.
     I'm not sure what the difference in converter stall is
    between the mild and hi-po versions (or if there even
    is a difference).

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