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  1. #1
    cerebral's Avatar
    Join Date
    Jul 2007
    Virginia, LKA, Colonial Beach

    Kawasaki 15F Single Muffler Free Flow Exhaust Upgrade Guide - 2009 and UP

    PART 1 - Why & What will be Upgraded?

    Kawasaki did us a big favor by removing the 2 muffler system AND the emissions systems in the 2009 and up 15F's... BUT (you knew it was coming) they crippled them by replacing the 60mm (2 3/8 inch) system with a 45mm (1.75 inch) setup. It might not seem like much but take a look at the muffler outlet pics below and you will see just how much they have restricted the flow to make up for the loss of the emissions hardware and still meet 3 star California emissions ratings (pic 1, 2 & 3).
    Click image for larger version. 

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    The original exhaust flange on the rear of the ski is actually 60mm tubing but they flange it out to 70mm at the very end of the flange, the pic shows the new OEM flange that stays 45mm from muffler to flange (pic 4).
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    To take advantage of any intake upgrades or Engine mods you will need to get the exhaust up to par, this guide shows the "no corners cut" method, you can probably save a few bucks with some creative work, or not top of the line parts that I tried to use.

    Please add comments, suggestions, or mistakes you might find in this thread as I would like to keep it a "living" document that we can change or add if needed.


    V 1.0 08.28.2010

  2. #2
    cerebral's Avatar
    Join Date
    Jul 2007
    Virginia, LKA, Colonial Beach
    PART 2 - Parts Needed & Parts To Be Removed


    The new parts needed are shown in picture 1, the prices listed are what I PAID, you might be able to get some cheaper, some might be more expensive especially when dealing with factors like eBay or forums where prices are liquid or can be negotiated.
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    A. 1x Primary Muffler from a 2003 ~ 2008 STX-12F or 15F (60mm outlet)
    B. 1x Brass 90 degree waterline 1/2 inch fitting (already installed on top of muffler with red LOC-TITE, not thread tape)
    C. 2x 2.5 inch (63mm) silicon hose couplers and 1x 2 1/2 inch TO 2 3/8 inch (60mm TO 63mm) silicon hose reducer (see notes)
    D. 1x Riva Aluminum Exhaust Outlet Cover (see notes)
    E. 6x 2.5 inch T-Bolt SS Clamps
    F. 2x 90 Degree 2.5 inch (63mm) Mandrel Bend Aluminum Tubing with approx 6 inches of length after the bend
    G. 1x OEM Exhaust Flange/Tubing from a 2003 ~ 2008 STX-12F or 15F (60mm tubing, 70mm outlet)

    H. 1x 2 Foot Section of 1/2 inch waterline hose (NOT PICTURED)
    I. 1x Brass splicer 1/2 x 1/2 inch Inner Diameter (NOT PICTURED)
    J. 1x Riva 45 degree Aluminum water bypass outlet (NOT PICTURED)

    A. Primary Muffler can be either drilled and rewelded, or a stock OEM, this upgrade will improve the exhaust greatly and allow you to get the most out of the modifications you have made to your ski intake or engine mods.
    B. I prefer the brass waterline outlets sold by as they are a bit longer with 4 ribs instead of 3 like the OEM.
    C. You can easily use 3 regular 2.5 inch couplers but the outlet on the primary muffler IS 60mm and a bit short and thick aluminum so I choose not to use an exhaust tubing expander like I did on the flange to work it to 2.5 inch (63mm), more on that later in the guide. When you buy the hose it will be sold by INNER DIAMETER unlike the aluminum tubing which is sold by OUTER DIAMETER. 2.5 inch hose fits OVER 2.5 inch tubing.
    D. This Flange Cover is for pure looks and rather expensive, you could easily cut the 90 degree elbow bend off the OEM flange cover and achieve the same effect or leave the OEM as is and it would cut the noise a bit if you have the drilled muffler since the gases will be directed down.
    E. T-Bolt clamps are much wider (almost 3/4 inch) than the regular OEM screw type hose clamps, I have NEVER had one fail. Be warned these things will not strip out like the worm gear OEM type; they will just strangle whatever you have them on until it’s crushed! In MOST cases when you buy 2.5 inch clamps they will FIT OVER the 2.5 inch hose, you do not need to up size unless specifically stated by the seller.
    F. Mandrel bend is the smooth bent pipe, don't try to use a regular pipe bender if you doing it yourself, I was originally going to find a straight 2.5 inch pipe and then find someone to bend it in the custom shape I needed but for this project that might be a pain for some people as I had to look for a while to find someone that was able to bend it with a mandrel bender, the machines are ridiculously expensive. 2 90 degree bends will achieve the same result with some minor cutting and the cost of a 10 dollar silicone hose is worth saving the trouble.
    G. OEM Flange and attached 60mm aluminum tubing as the OEM ones on the new 2009 and up 15F's have a weak 45mm outlet just like the outlet on the OEM muffler (WEAK!). This will be cut to leave just a straight pipe and the flange.
    H, I, & J - These 3 parts are for the waterline bypass that will be installed after/during the exhaust upgrade, pictures and instructions will follow the main guide


    A. Muffler - $75 (eBay)
    B. Brass Fitting - $4 (atlanticjetsports)
    C. Silicon Hoses - $11 each for the 2.5 (63mm) straight, $22 for the reducer hose 63mm>60mm (
    D. Flange Cover - $50 (RivaRacing)
    E. T-Bolt Hose Clamps - $2.20 each x 6 (10 for 22 dollars on eBay)
    F. Mandrel Bend 2.5 inch Tubing - $18 each (eBay)
    G. OEM Flange - $40 (eBay)
    H, I & J - $35 (RivaRacing)

    SHIPPING WAS NOT INCLUDED IN PRICES (E, F & G did have free shipping, I paid 20 to ship the muffler)

    Picture 2 shows the main 3 parts we are getting rid of.
    Click image for larger version. 

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    Step 1. Start by loosening the clamps on the black hose that connects the primary muffler with the aluminum tubing/flange, remove.
    Step 2. Loosen the clamps holding the primary muffler to the exhaust header on the engine; if you completely loosen them you should be able to slide the blue silicon hose forward towards the bow. WARNING* Under the blue silicon hose on the header there are 2 PISTON RINGS, yes piston rings that are used to seal this joint, take note when doing the muffler removal to make sure these are still in place, and not too old, otherwise replace. Unhook the black strap over the muffler and remove the primary (keep the bottom brass single fitting, the double on the top is useless as we will install a bypass for one of top lines later).
    Step 3. Remove the 3 Allen bolts holding the black 90 degree elbow cover off the back off the hull flange area, remove the outlet. Under that you should see the actual flange that the aluminum tubing connects to, take the 4 Allen bolts out and remove the whole flange and aluminum tubing by pulling the whole thing out the hole.

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