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  1. #1

    Releiving the exhaust above the Cavitation plate?

    I have heard of people relieving the exhaust just above the cavitation plate on an outboard motor. My question is, is there any significant gain in doing this other than making the motor louder for bragging rights? Where and how are they exactly releiving the exhaust? Are they drilling holes into the midsection above the cavitation plate?
    BTW:
    I know I'm full of questions guys but I'm new to all this High Performance Boat stuff and I'm trying to learn all that I can.

    Thanks again:
    Jason

  2. #2
    Join Date
    Apr 2001
    Location
    WASHINGTON N.C.. I TOO HAVE A BOATING PROBLEM
    Posts
    10,110
    Jason,

    I am from washington, and probably have seen you on the Tar River, (I am the guy with the blue Hydrostream and long ponytail that is always riding wheelies).

    If you ask Raceman, he will say it makes no differance, (mabey on take off), I notice better midrange accelleration, and if I plug the holes, I notice a slight loss on top.

    What does your boat look like?

    What motor and size?
    JOHN MASON
    '83/VECTOR/MERC 200-- SOLD
    '98 Quartershot T-3/ MERC 200




    "If your not living on the edge, your taking up to much space"

  3. #3
    Waterwings,
    I have probally seen you some time or another on the tar river. I haven't there in probally a year because my parents bought a place in Swansboro on the intercoastal waterway. The boat I have is a 17' Red and White Sunbird with a 115 Evinrude off the back. The boat is an older 1985 style. Where did you drill your holes at and how big did you drill them? Also how many holes on each side of the lower unit did you drill? Did it make the motor louder once you got up on plane?

    Thanks:
    Jason

  4. #4
    Join Date
    Jan 2003
    Location
    Georgetown,SC
    Posts
    1,156
    I not far from both of yall.Lets swap props or stories some time.I have a blue with yellow checker board on the rear of my 85 action marine.Its actually a modified version of the hydrostream ventura.By the way i just bought a laser II 26 p prop for the boat .Iam building a mod 200 2.4. Is this a decent prop for it?

  5. #5
    Does anybody have any pics that they can post so I can see exactly how it is done? I don't know what size to drill the holes and how many on each side do I drill?

    Thanks:
    Jason

  6. #6
    Join Date
    Apr 2001
    Location
    WASHINGTON N.C.. I TOO HAVE A BOATING PROBLEM
    Posts
    10,110
    I have used 1-1/2" hole saw on the rear of the mid, one hole on each side, at the bottom of the mid, I also removed the mid and drilled 5, 1/2" holes each side (on the inside so that they can't be seen)

    I have seen it done many ways in different places, even in the center middle of the sides of the mid, even in the lower unit, but most are in the lower rear of the mid, (these are on mercs)

    Sorry, I don't have any pics.

    Hydro1, I run a 26 Trophy 4 blade that I like, it runs 88.3

    I also run a 28 inline chopper for speed runs, it runs 94.1

    But the Trophy is the best of my all around props, I did run a 25 Marage, but after running the 4 blade, I wouldn't go back to the 3 blade.
    Last edited by WATERWINGS; 07-10-2003 at 09:13 AM.
    JOHN MASON
    '83/VECTOR/MERC 200-- SOLD
    '98 Quartershot T-3/ MERC 200




    "If your not living on the edge, your taking up to much space"

  7. #7
    Waterwings,
    When you say at the rear of the mid, one hole on each side are you talking about drilling them so if you were standing beside the boat looking at the side of the motor that the holes would be close to the boat where you could see them or would they be on the backside of the mid? Hopefully that question was not too confusing. LOL
    Thanks:
    Jason

  8. #8
    Join Date
    Apr 2001
    Location
    WASHINGTON N.C.. I TOO HAVE A BOATING PROBLEM
    Posts
    10,110
    At the very rear of the mid, pointing straight back on a merc.

    I can't see in my mind how a evinrude is shaped at the rear, but a merc is kinda flat at the lower back of the mid.

    Enough room for two 1-1/2" holes.
    JOHN MASON
    '83/VECTOR/MERC 200-- SOLD
    '98 Quartershot T-3/ MERC 200




    "If your not living on the edge, your taking up to much space"

  9. #9
    Join Date
    Nov 2001
    Location
    Lake Charles, Louisiana
    Posts
    6,784
    Here is one way to drill the mid.
    Attached Images Attached Images
    -----------------------
    93 STV Mod VP/MERC 2.5 200
    -----
    “Do not judge others, and you will not be judged. For you will be treated as you treat others. The standard you use in judging is the standard by which you will be judged."

  10. #10
    Join Date
    May 2003
    Location
    Tarpon Springs, FL---Queens,NY
    Posts
    14,979

    hey i need help 2

    i have a 19' baja with a 1994 200 johnson venom and i was wondering what prop i need i know i need alot more prop because im only doing 50 and i am gettting 6300rpm opened up trim up (no jackplate yet! ) i m runnin a 15x17 ss but i need more alot more i need to drop the rpm down to about 5500 or so ok thanks for your help boys

  11. #11

    relief

    heres mine drain plugs will fit it if you want it quiet again.
    Attached Images Attached Images

  12. #12
    Join Date
    Nov 2001
    Location
    Coppell, Texas
    Posts
    501
    Use Bob's Outboard Exhaust Housing.

    c/6

    Hooty
    c/6

    Hooty



    /team2004.gif[/img]

  13. #13
    Join Date
    Oct 2001
    Location
    Voorheesville, Upstate NEW YWAK!
    Posts
    2,864
    Check out the metal fabracation section. I have some pictures of a exhaust snout that I made with a couple of 1-1/2"x4" holes.

    Tom

  14. #14
    Join Date
    Nov 2001
    Location
    Coppell, Texas
    Posts
    501
    Here's Bob's setup. Requires one 2" hole through inner and outer exhaust housings.



    c/6

    Hooty
    c/6

    Hooty



    /team2004.gif[/img]

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