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Thread: Lower Plenum ?

  1. #1
    Member Feedback Score 0 Primus101's Avatar
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    Lower Plenum ?

    Dear Gearheads,
    I'm sure I've read somewhere that you have to be cautious about torqueing the lower plenum down due to potential cracking- or warping?
    In the FSM I noticed that there's a change in torque specs from Nov. '93.
    It's a fairly substantial change- up to Nov.'93 11lbs max, after that 17lbs.
    Did they upgrade the material in the casting?
    I have done some port blend refinements on my '93 lower(pre Nov.), but I do have a '95 lower and am wondering if I should be using it instead-they both appear identical, same casting marks.
    My '93 TT is a 4 bolt.
    Thanks in advance

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    The one. The only. verified Feedback Score 11 (100%) stealthee's Avatar
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    Quote Originally Posted by Primus101 View Post
    Dear Gearheads,
    I'm sure I've read somewhere that you have to be cautious about torqueing the lower plenum down due to potential cracking- or warping?
    In the FSM I noticed that there's a change in torque specs from Nov. '93.
    It's a fairly substantial change- up to Nov.'93 11lbs max, after that 17lbs.
    Did they upgrade the material in the casting?
    I have done some port blend refinements on my '93 lower(pre Nov.), but I do have a '95 lower and am wondering if I should be using it instead-they both appear identical, same casting marks.
    My '93 TT is a 4 bolt.
    Thanks in advance
    Never heard of issues with cracking the lower plenum. The main issue is people overtightening the upper plenum stripping the holes out. The holes go into the lower plenum.

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    Better than that "other" place Not Verified Feedback Score 2 (100%) x2xtreme360's Avatar
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    Make sure you hand tighten all the nuts until you can't anymore... then tighten each one a quarter turn to seat the manifold. After that, do half turn increments on each nut until it's nice and snug.

    And as Stealthee said, the upper and lower manifold are made of aluminum... stripping the holes in the lower manifold that the upper plenum bolts to is BEYOND easy so be careful.

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    Member Feedback Score 0 Primus101's Avatar
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    I'm refering to torqueing the lower plenum to the heads-
    Steel stud, 'bearing washers' & nuts. Side to side tightening sequence.
    Looking for some insight as to why the torque rate for the lower plenum is approx. 60% higher on '94 models.....?

  5. #5
    Forum User Feedback Score 3 (100%) toddrs93's Avatar
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    Odd, but thats not really an area that needs to be real exact. A good gasket and a reasonable crank with a 3/8 ratchet is all you need.

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