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  1. #1
    dcuhpw's Avatar
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    15f Exhaust mods that work

    Curious to see what the consensus is regarding any 15f exhaust mods. I know the pre 09’s could upgrade to the Riva exhaust and it was 2.25” pipe iirc. The itty bitty exhaust on the 09 and later with the single waterbox seems excessively restrictive. My calculations are that at least a 2” exhaust is needed for stock HP. However, as much water as the waterbox holds it is likely that there is enough restriction there that the tiny 09+ exhaust pipe is sufficient. So that turns the attention to the waterbox. I haven’t seen any aftermarket water boxes. Has anyone had good success modifying one or running a straight pipe setup? If so please let us know what you did specifically and the results. Thanks!

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    dcuhpw's Avatar
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    Just to update, the exhaust manifold inner diameter is 2” so that would be the max through size I suppose. The waterbox inlet is 1.75” and outlet 1.5”. Quite a bit of restriction there not to mention the 1/2 ton of water in the box while running.


  3. #3
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    Quote Originally Posted by dcuhpw View Post
    Just to update, the exhaust manifold inner diameter is 2” so that would be the max through size I suppose. The waterbox inlet is 1.75” and outlet 1.5”. Quite a bit of restriction there not to mention the 1/2 ton of water in the box while running.

    DO NOT RUN A STRAIGHT PIPE the engine will suck water up the manifold and hydro lock the motor.

    Sean

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    dcuhpw's Avatar
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    Quote Originally Posted by smokeysevin View Post
    DO NOT RUN A STRAIGHT PIPE the engine will suck water up the manifold and hydro lock the motor.

    Sean
    Sounds like the voice of experience lol. What about the old style box with the Riva mod?

  5. #5
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    Quote Originally Posted by dcuhpw View Post
    Sounds like the voice of experience lol. What about the old style box with the Riva mod?
    Yep, learned it the hard way all in the name of testing. Riva mod is fine if you follow the directions exactly.

    Sean

  6. #6
    dcuhpw's Avatar
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    Quote Originally Posted by smokeysevin View Post
    Yep, learned it the hard way all in the name of testing. Riva mod is fine if you follow the directions exactly.

    Sean
    So here is the plan: 49070-3744 water box (new or used), Riva mod (1.75” hole drilled in baffle), and run a larger exhaust outlet. Question is what to use for the waterbox to outlet tubing/hose.

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