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  1. #1
    Join Date
    Jan 2010
    Posts
    89

    Installing thruhull exhaust

    Hi all,
    I have an 1990 175 Thompson. I am very interested in installing a thru hull exhaust on this boat for that v8 sound and to get more out of the motor and to be better on gas mileage while fishing. This boat sounds great when running out of the water but too quiet while in the water. I need to know if I would have to change my original exhaust manifold? Can I just put on a header? Do I need to install anything special in the transom to protect from heat or to seal around the exhausts? How to keep water from coming up the old fart pipe? Any particular size of pipe be better? One of my buddies works at an exhaust shop and said a glasspack on this thing would make heads turn. One last question, I have a hole saw , anyone wanna come over and help?

  2. #2
    archerytech1 Guest

    RE: Installing thruhull exhaust

    Just a wild guess but maybe to fabricate your own it may need some sort of loop in the exhaust to stop water from entering heads... Like I said, I really have no idea but loop sounds good :-)
    Shane
    Pro-Line 190
    Home Ports:Mich city,IN &
    St.Joe,MI

  3. #3
    Join Date
    Jul 2007
    Location
    Eden Prairie, MN
    Posts
    2,202

    RE: Installing thruhull exhaust

    Why in the world would you want a loud exhaust while fishing? Is this a 5'6" with a mustache type of thing? Unless you have a high performance boat, you're not going to see any noticeable change in fuel consumption or performance.

    I don't know the specifics of what's involved but it involves more than just a couple of headers and a hole saw.
    Eric
    '87 Four Winns 245 Vista named "Cousin Eddie"
    "Now Clark, don't you go fall'n in love, she's coming with us when we leave here next month".

  4. #4
    Join Date
    Jun 2006
    Location
    De Pere WI
    Posts
    111

    RE: Installing thruhull exhaust

    Of course you realize that all marinized engines have water cooled exhaust manifolds. Right?

    I hope you are joking if you think you can put "headers and glass packs" on a boat....

    I think a commercial version of the thru hull exhaust is called "captains call". this allows you to have a quiet/obnxious lever.

    Once installed, boaters use them twice then leave them in the quiet position.

    Personally, I love having a kicker motor on my boat that makes very little sound.

    Not trying to be a tool, but my guess is the exhaust fumes and noise would make thru hull a real PITA in two trips or so....

    http://www.boatstoreonline.com/corsa.html

  5. #5
    Join Date
    Sep 2006
    Location
    Ellison Bay, WI
    Posts
    4,207

    RE: Installing thruhull exhaust

    I think the water cooled manifolds are there to keep the boat from catching fire.

  6. #6
    Join Date
    Mar 2005
    Posts
    76

    RE: Installing thruhull exhaust

    Here's what you will need to consider should you decide to go forward with the project.

    1) You'll have to install two exhaust tips - one for each exhaust manifold on a V8. They will install thru the transom directly behind the exhaust manifold elbows. You'll need to cut holes in the transom with a hole-saw. The tips will be 3" or 4" depending on the vintage of your engine. The newer mercruiser alpha drives are 4" output the older ones were 3". These exhaust tips typically will exit the transom above the water line but you could install customs that would exit below the water line so that the exhaust tips are only out of the water when the boat is on plane. You will need either internal or external flappers on the the tips to prevent water backing up into the engine. Also, you may have to install muffler inserts into the tips if you plan on running the boat where they check for that sort of thing with a noise meter. If your boat is an older mercruiser with the log style manifolds you'll have to convert to the newer style manifolds before you start, but then you'll be starting off with the 4" outputs.
    2) If you install plain old thru-hull's you'll have to block off the Y-pipe. This can be done by buying special rubber caps that install on top of the Y's and attach with 2 stainless hose clamps per side of the Y. You could also yank the engine, remove the Y pipe and install a special Y-pipe block-off plate. The block off plate is the better 'look' if you don't mind yanking the engine to do this.
    3) You can also install a switchable diverter Y system which will allow you to select between thru-hull exhaust and thru-prop exhaust. This is an additional Y that connects the exhaust elbow to both the thru-hull tips and the original Y pipe. This approach doesn't require blocking off the original Y pipe since the thru-prop exhaust will still use the Y. The diverters either use an electrical solenoid or a air cylinder to switch a flapper within the special diverter Y. Although costly, this is the better approach since it gives you fingertip control of both thru-hull and thru-prop. I'll try to attach a picture of this set-up. Note that in this photo the elbow was also replaced with a custom stainless elbow. You really don't need to replace your elbow. Also note the thru-hull tip will connect to the elbow with special wet exhaust grade rubber hose which is readily available.

    I have a 26' formula sportfisher with twin 350's. It already has the thru-hulls installed but has the block off plates instead of the Y pipes. Since the holes are already thru the transom instead of just blocking them off and going back to a conventional thru-prop exhaust I'm in the process of installing Y-pipes and a switchable diverter Y system (Corsa) so that I can select between thru-hull and thru-prop exhaust. There are a lot of times where it is fun to just run the exhaust thru-hull but trolling is not one of them. It makes for a long day.

    There is some horsepower gain with thru-hull exhaust due to reduced back pressure but its only estimated at about 10-20HP so that would be a lot of work just to gain a bit of power.

    If I had a boat that had thru-prop exhaust I don't know if I'd go through all the trouble, but if I did want to do it, it would have to be the switchable type because I wouldn't want to troll all day with above-water exhaust such as the thru-hull.


  7. #7
    Join Date
    Nov 2005
    Location
    IL/WI State Line
    Posts
    83

    RE: Installing thruhull exhaust

    I loved the sound of the big block with my Corsa trough hull exhaust and it would sure turn heads at the ramp when I fired it up.

    I must be getting old, but the loud motor noise and the exhaust drifting back into my boat got to me after 10 plus hours trolling. I installed a Gill Marine DGM silencer system. Now the exhaust diverts underwater when I am going slow and above the water when it is up on plane. Way more fishing friendly.

    If you are very handy, you can get a Corsa system for a couple of grand and install it yourself. It is a lot of work. That is why I elected to use a bolt on silencer instead of switching to captains call. Check the go fast boat websites. Those guys are all over that type of stuff.

    By the way - I posted this for guys who might have a similar issue with their exhaust. Not for JeffM who is obviously pulling our leg.
    Good Luck and Good Fishing - John

  8. #8
    Join Date
    Aug 2008
    Location
    Algoma, WI
    Posts
    1,780

    RE: Installing thruhull exhaust

    As stated- you'll probably enjoy it for about the first 10 minutes and then want to silence the noise, it's one thing to have inboards with exhaust 'cans' rumbling a bit, but it's entirely different to have pipes coming straight off the exhaust elbows and listening to them slapping for hours on end. I say leave it to the sport boat guys.

    -Champ

  9. #9
    Join Date
    Dec 2006
    Location
    Pipestone, Mn
    Posts
    2,584

    RE: Installing thruhull exhaust

    Would it be cheaper and easier to put a GREAT stereo in with a CD of motor noises??? Just a thought, I have a Harley Davidson mp3 that I play on my goldwing that seems to turn heads. :P


    http://i224.photobucket.com/albums/d...rboy1/0008.jpg

    Rod's R&R
    LAKE MICH./WEST SIDE

  10. #10
    Join Date
    Apr 2009
    Location
    right hear
    Posts
    160

    RE: Installing thruhull exhaust

    You got a v8 in a 175 thopmson?

  11. #11
    Join Date
    Feb 2012
    Location
    Clovis ,new mexico
    Posts
    2

    exhaust flaps?????

    i am in the prosess of fabricating my own thru-hull exhaust through the side on my boat.. i am curious if i absolutely need to install the flappers on the exhaust tips??? any thoughts will be greatly appreciated

  12. #12
    Join Date
    Jan 2011
    Location
    Briggsville,Wi.
    Posts
    170
    REALLY!why on earth would you,or anybody around you want to listen to that noise when it is supposed to be a relaxing time?you better get your spread well away of the boat cuz they will know you are coming.i knew a guy that did that some years back and he ended up selling the boat for whatever reason..good luck with your decision,but maybe give it alot of thought.

  13. #13
    Join Date
    Feb 2011
    Location
    Munger, MI
    Posts
    235
    You are going to scare away fish if they are running high, and also get alot of funny looks while in harbor patrol. I think you should buy a cheap cigar boat and have the best of both worlds.

  14. #14
    Join Date
    Feb 2012
    Location
    Clovis ,new mexico
    Posts
    2
    i have already cut the holes the decision has been made im just not shure about the flapps in the exhaust tips

  15. #15
    Join Date
    Jul 2003
    Location
    W. Michigan
    Posts
    5,064
    If you slip the boat and fire it up at 4am to go fishing, the people around you at the marina, with hangovers, who went to sleep an hour ago, will be waiting for you when you come back. I don't have through hulls but we still slid out boat out of the slip, pushed it into the current and fired it up beyond the marina as a courtesy.
    I buy my own tackle, as cheaply as possible.....

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