DIY PWC muffler project

[TimeBandit]

I often use a '05 FX HO to augment short fishing trips. Fishing means the ski might see long periods adrift and/or at anchor in open waters engine off. Maybe it's just me, but the oem exhaust loop seems to be but a hair above the waterline. Loaded down with gear and fishing off the rear, causes it to list a little deeper. Therefore, increasing the loop height in the exhaust system would better insure water isn't going to reverse-flow into the waterbox/lock. So I gutted the oem exhaust components, cut a hole in the rear, and being an older craft, I went with a DIY free-flow thru-hull setup. Works & looks great, BUT things are a little LOUD for my tastes. Also worth noting that this ski has a 2012 1.8L HO engine (not the MR1), so there's a pretty bad drone at around 3K-4K rpms (yes, even with a thru-hull port).

Being I've fabricated/modified motorcycle exhausts past, I decided that I'm going to attempt a "PWC muffler" of sorts, and located it just before the hull exit port. And being a wet-system, use of packing and other suppression materials are out of the question. I'll simply have to rely on good-old baffling to help break up the decibels somewhat.

{baffle design blueprint}

So I mocked-up this simple two-pipe construction (pic above), all aluminum, a larger 4" tube as the body, and a smaller 2" tube as a baffle. Hopefully the transitioning up to 4" diameter will compensate for any flow restrictions baffling might introduce. The entire baffle chamber being just 12" long.

{baffle tube fabrication}

Hey, no rhyme or reason with the placement, size, shape of the baffle tabs. I'm not a sound-science wizard, no fancy exhaust simulation software . . . just trying to disrupt the pressure waves here. I also wanted to avoid any substantial restrictions, as I still wanted this a free-flowing system. I figured these wedge-shapes were the easiest to cut with the tools that I have (Dremel), and leaving just enough uncut on the end will enable me to bend these tabs into 45deg baffle wings. Hopefully this will direct opposite sides of the pressure waves to collide and cancel.


Next is to figure out how mount the baffle into the 4" tube . . .

[TimeBandit]

Moving right along . . . I thought it best to weld the baffle into place, as to prevent vibration and noises had I chose to just press-fit only.

{Inserting the baffles}

Started out by TIG welding four standoff pegs into the baffle tube. Press-fit / inserted the baffle assembly, then drilled 4 strategic holes in the body tube where the pegs are positioned. The drilled hole exposed the peg face, to then I welded a fill divot into the holes. Came out SOLID.
Weight? Not bad. Being all-aluminum, there really isn't much weight to it.

{gas-flow}

As you'll note in the pic above, looking down the throat shows that the exhaust gases will still have a straight path through the muffler, yet the pressure waves will fall into the baffle tabs (I hope).


. . . Next up will be installation into the ski.

[badjoka]

Can't wait to see how it turns out.

[TimeBandit]

Ok, with the sound-suppressor fabrication a success, it's time to mount it in the craft . . .

{ all components laid-out }

Here are all the parts acquired (pics above). The down-side with such a DIY system like this is all the many clamps & connections. Basically, you're looking at cold-air intake parts, consisting of 3mm thick aluminum tubes with 500deg F 4ply silicone couplers/unions.

{ system installed }

Here's a shot (above) of this system installed in my '05 FX HO with the VXR motor. All fits pretty well and snug. I've since added a support strap to the upper neck of the exhaust loop for good measure. You can see just how much higher the loop is in that pic !

The Centek exhaust port is on the stbd side. I found the old oem port useful for reaching my hand through. Speaking of the OEM port, it was blocked-off with a large PVC cap top cut out. Yes ! It's much cleaner back here, and I've gained some added storage space!

Next ÔÇô up : need to start it up on the hose, then get it out on the waters

[Reaper9789]

looks really good man!

[birel33]

While I don't think this is for me, I am looking forward to hearing how it worked out and hopefully some before and after videos. Even if it didn't work I'd love to hear more about it and see the results. It's innovation such as yours that is the heart of our hobby!

[TimeBandit]

SUCCESS !!


Got it tested in the driveway the other night. WOW !!! That sounds mean! Here's what's going on ( I think ). . . apparently going up to the 4" tubing deepened the rich sound at idle, like it added bass to the exhaust-note. The pulses-per-minute (PPM) at idle are just not fast enough for the baffling to effect it. However, and this is the really cool-part, rev'ing it up actually mutes that ear-piercing rasp note. Likely the higher PPM are matching the baffles and getting hung-up / broken-up more so. It kinda gets that stock-classic hummmm'ing that a 4-stroke sounds like. Can't attest to any drone characteristics yet, as it's hard to tell on the hose. I pretty happy so far - can't wait to get it out on the water now.

[badjoka]

Forgot about this thread, how did it sound on the water?

[TimeBandit]

I tried a few times my S6 phone, but never got a decent clips. Either too much wind-noise, or it was something else. I need like a decent recorder to do this thing justice. I'll get one posted up here one-day.

So as I described previously, it idles like a un-muffled straight-thru (rich deep deep jet-boat sound), yet quiets to a normal (slightly louder than stock) classic wave runner hummmm at speed. I have no exhaust tuning experience, but is seems it's inherent design (spacing of the baffle wings) attenuates the faster RPM pulses - which is exactly what I wanted.

[badjoka]

Thanks for the update and glad you like it. I'm going to try for something similar, or adding a resonator pipe like Nashvegas did.

[wheresmike]

TimeBandit followed you from the other thread.. I only ask the questio because I had the same thought but figured if I did a baffle in some way it would cause some restrictions and then be no better off than stock.. did this get rid of all the drone noise?

[TimeBandit]

Okay, if we were to rate the typical free-flow & rear hull exit ported exhaust at let's say 100% nauseating in that so-called 3-4K RPM droney range . . . then I'd say this baffle mod has cut 75% of the volume. At WOT, it gets even "quieter". I'm no exhaust tuning expert, as I'm sure there's much science in this, and probably with computer simulations one could extrapolate the precise mm and baffle offset length to kill the frequency in question, but for me, this fits the "good enough" category. The key concept in baffle systems that do not restrict flow rates, is to understand that sound (pressure waves) propagate way faster than the rate of the exhaust gases. So this design allows for 4" increase in diameter as not to restrict volume of flow, yet the pressure waves will get caught up / sliced up in all that extra angled surface area.