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Thread: Water Box Mod

  1. #1

    Water Box Mod

    So the boss has this 04 RXP that I am currently working on. AND just got an 08 RXP-X. I've read here about shortening the water box. Since we are a fabrication shop it would be easy to do if I had a clue.

    How short do I make it? Are there internal parts that need any work?

    Thanx in advance. Send Pix if you can (of the water box!), I'm a real visual guy!!


  2. #2
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    You can shorten the 04 waterbox, you CAN NOT shorten the 08+ waterbox due to the water entry of the exhaust.

    On the 04 box, open the front end (towards SC)...Cut the flared outlet and make it flush, and in the baffle wall make a 5" hole. This will give you the BEST flow over a shortened box. I've modified atleast 2 dozen boxes this way and its the best way to go...Free flowing and DEEEEP sound

    SAME modifications on the 08 box, open it up and remove the flared outlet...and open up the baffle wall as much as you can...I use a 2" hole saw to make several holes until the baffle is gone.

    For flow information, check here...
    http://greenhulk.net/forums/showthread.php?t=97790

  3. #3
    Doesn't say how short to make the box.

    Also, As I read in one of the other posts, can the J pipe be trimmed at the exit end? and how much?

  4. #4
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    Quote Originally Posted by melcraven View Post
    Doesn't say how short to make the box.

    Also, As I read in one of the other posts, can the J pipe be trimmed at the exit end? and how much?


    Shortening the waterbox can be ANY length, and from my testing, I do not recommend it. Reason is that varying length will change the waterflow/airflow dynamics internally, which can vary based on how much material internally you remove.

    This can cause water to either pool up and choke the outlet, or not flow in the right direction and cause a hot spot, which can burn through...a host of issues.

    But if you want to shorten it, which you will get a "ting-ting' sound like a motorcross bike, then you simply need to cut the BACK of the box and remove enough material until you get to the middle horizontal baffle (you'll see it)...THAT BAFFLE must remain there to help prevent burn through in the event of water starvation of the system. If you remove that, you are on your own for the rest of the system. If it burned through it will fill your hull with water and exhaust...

    Jpipe trimming, don't...This will change the torque curve/response of the motor at specific RPM...PLUS increase backpressure. If you have the ability to expand pipe, simple flare will do wonders to flow...

  5. #5
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    I shortened my 2008 water box a little over an 1 1/4 and added about that to the neck to gain a little more clearance for the thru hull and to make supercharger removal alot easier. I have a 2005 RXP. I have not seen ANY adverse affects in doing this. My boat currently runs 81.8

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