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  1. #1

    Default Replacing mufflers with straight pipes.

    2001 Moomba Mobius. All measurements, parts, and pictures are based on this boat. Your boat may vary. I had to split this up into several post to get all the picture in. You can see my pics at:

    I noticed my muffler was leaking, and after looking at how poorly they are constructed, I decided to simplify the exhaust by replacing the muffler with a straight pipe. There should not be any issues with the performance of the motor. In fact, I might gain a couple of HP as the exhaust is now more free flowing. The only thing to consider is an increase in exhaust noise. For me, I like my carbon footprint to be loud! Plus, with all the music coming out of the boat, motor noise is my last concern.

    My exhaust exits the manifold and enters the muffler at 3 1/2" I.D., then exits the muffler at 3" I.D. This 3" line then continues to the exhaust exit at the back of the boat.

    Through eBay, I found Ashland Muffler House, Inc.

    For about $60: They sold me a 5' piece of 409 stainless 3" O.D. tubing. Cut it in half. Put a 30 degree bend at the end of each 30" pipe, leaving 4" of straight pipe. Here, you can see the pipes, placed next to the mufflers:

    HINDSIGHT: If I'd known that I was reducing from 3 1/2" to 3", I would have asked them if they could flange the short end to 3 1/2", saving me the headache of sleaving the small pipe to fit into the large one. I'd also have them bend the tube to 45 degrees.

    This is a picture of the pipes inserted into the large rubber exhaust:

    In this configuration, the tail of the SS pipe, overlapped the 3" rubber by 7":

    Since I'm not going back to the mufflers, I cut off 3 1/2" of this rubber exhaust to use as a sleave for fitting into the larger rubber pipe at the manifold. I used the clamps as a guide to cut. I then inserted the short end of the pipe into the sleave, giving me a perfect 3 1/2" O.D.

  2. #2

    Default Page 2

    I lubed everything up with a lot of WD40, inserted the 3" end into the 3" rubber, and then muscled the sleaved 3 1/2" end into the 3 1/2" rubber:

  3. #3

    Default Page 3

    Clamped everything down:

    I went to the boat ramp and checked for leaks. At the lower RPMs, I did not notice much more noise. The installation was clean and simple.

    Afterwards, I used the old muffler clamps to secure the exhaust. I was also careful to route and zip tie all electrical wires, hoses, or anything else that could melt well away from the SS pipe. It will be hotter than the mufflers.

  4. #4

    Default Page 4

    Addtionally, I replaced the the shaft log and repacked the gland nut. To do this, I had to remove the prop shaft flange. I simply put a socket between the flange and the transmission, tightened the bolts, and it popped loose very easily:

  5. #5

    Default Page 5

    Here's a picture of all the parts cleaned up and ready for assemble. NOTE: I was only able to use two of the packings.

    I'll let you know what the noise level is like once the winds calm down and I get on the lake. I'm really not worried about it.


    KISS: Keep It Simple Stupid

  6. #6
    Join Date
    Aug 2009


    definitely post up some video with the sound of that when you are done if you can

    2007 Moomba Outback - going, going, GONE
    2015 "NOT A MOOMBA"

    Why Not? Play Hard! Get wet

  7. #7
    Join Date
    Jul 2009

    Default Exhaust Replacement

    I am in the same situation as you were. My exhaust is leaking and I have to do something.
    I was wondering if you tried it out yet and found out how the sound is?
    Also, does the pipe get to hot?

  8. #8
    Join Date
    Jul 2009

    Default Exhaust Replacement

    Sorry, I just saw your last posts about the sound, that's great, but still wondering if the new exhaust pipe gets to hot?

  9. #9


    Quote Originally Posted by outbackhead View Post
    Sorry, I just saw your last posts about the sound, that's great, but still wondering if the new exhaust pipe gets to hot?
    I haven't actually done any testing to see how hot the pipe gets, but I'm sure it's warm. I've been careful to route everything clear of the pipes. I don't think it'd get too hot, as the mufflers look to be made of PVC and or plastic. I think I've even read where some people have used PVC in this area?

    Once the motor is off, they get water in the pipes to cool them down, as well.

    Good luck.


  10. #10
    Join Date
    Jul 2009

    Default Exhaust Replacement

    Thanks for the info.
    I'm going to go the same route as you because I just priced new mufflers and they are $325 each and mine are leaking enough that I have to do something.
    So I will get the short end flanged out to 3 1/2 inches and the angle to 45 deg. like you said.
    I will let you know how it goes.

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