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  1. #1
    Join Date
    Dec 2016
    Posts
    208

    Default Exhaust manifold swap

    Hey guys,

    The pcm exhaust manifold and risers are NLA or crazy expensive.

    There are aftermarket ones available from Barr, but still pricey.

    There are manifolds for other marine 454's like mercuriser etc. Which are cheaper...what's involved with changing to a different style on a full cap off rebuild?

    Thanks for your thoughts

  2. #2
    Join Date
    Dec 2016
    Posts
    208

    Default

    So after researching around quite a bit here's what I've decided to do. I thought I would share in case anyone else needs it down the line.

    Part # Chva184 - BBC manifolds
    Part # 20-0097 - 3" spacer block
    Part # 53-2027 - Barr/imdmar Riser with 3.5" OD outlet

    This keeps the longer riser putting the water /exhaust mix further from the exhaust flange and keeps a very similar geometry to the original PCM manifold/riser. It also keeps the 3.5" outlet to match the original PCM riser which is NLA.

    The total height difference between what I plan to go with and the OEM is ~ 9/16" measured from the center of the manifold flange to the highest point of the riser. If I remember i will post up a picture or two once the new parts come in.

    I did also consider looking at the Barr risers but these put the water/exhaust mix closer to the block than OEM and they also come in either the 4" or 3" outlest vs the 3.5" OD.
    Last edited by Cooose; 01-23-2018 at 05:32 PM. Reason: Corrected & added Part numbers

  3. #3
    Join Date
    Jul 2007
    Location
    Flowery Branch Georgia
    Posts
    2,742

    Default

    pics would help with what you are describing.

  4. #4
    Join Date
    Dec 2016
    Posts
    208

    Default

    Ok, here's some pics to try and illustrate what I'm talking about.

    Existing PCM manifold & Riser, note the water mixes w/ exhaust at roughly the 15" mark.



    Here's the replacement Barr equipment, here the exhaust mixes at roughly the 12" mark. The Barr equip has 3 pcs, 1 = manifold, 1 = 3" block, 1 = Riser



    The purpose of the 3" block serves 2 functions. 1 - Addresses a clearance issue shown below where the riser is contacting the manifold preventing a flush surface where it blolts to the manifold



    and 2 it keeps the total height from the center of the block exhaust port to the top of the riser to be within 9/16th of OEM.



    Instead of using this particular riser (53-2027) with the 3.5" OD output, there are 2 other options available. One is 20-0082 with a 3" OD, or 20-0100 with a 4" OD, however these two risers have the exhaust gas & water mixing at roughly the 8.5" & 9" marks respectively.
    Last edited by Cooose; 01-23-2018 at 05:38 PM.

  5. #5
    Join Date
    Aug 2010
    Location
    NJ
    Posts
    1,393

    Default

    Reversion will not be an issue with any of those options if running a stock cam. Also keep in mind you should be measuring the vertical rise as well in the distance before mixing water, since some have spacers. Personally I'd be looking at performance manifolds or shorty headers if I ever have to replace my manifolds.

  6. #6
    Join Date
    Aug 2013
    Location
    St. Louis
    Posts
    188

    Default

    Kudos for getting the manifolds off the block. I replaced the gasket between the risers and the manifolds a couple years ago. Took some real patience and PBblaster to get those out. Some of them were a hot mess. My manifolds seem a little rusty on the bottom exhaust ports. I thought about removing them and cleaning up/painting, but they don't leak and the bolts look ugly to get off ... so I'm going to leave them well enough alone.

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