My '01 Response came with the same Primex silencers that pretty much every Response prior to 2015 had standard. There was an optional quieter version that included a crossover tube to take the edge off the opposite banks firing, but most did not order this option. These stock silencers are hardly better than straight rubber tubes. They sound and flow great, but the sound out the back can be intense and it carries across the water a long way. As I'm often on the lake as early as 5am in the summer (public water, lack of sleep is necessary evil), I thought I'd try to see if I could quiet the boat down a bit without much effort. I had seen on another site that folks had success with this modification so I thought "what the hell?"
For 40ish bucks at Home Depot, you can pick up two 4" Clay to PVC Nibco couplers and a pair of 4" to 3" ABS or PVC closet elbows. If you have a Malibu with a Wedge, you will need to shave the Nibco down a bit to fit over the outer ring of the standard exhaust port. I just did a rough cut as a proof of concept (thus the rough appearance) and eyeballed how much to cut off to get the outlet to be right at the waterline when underway. On my boat, this meant pretty much cutting these off 1/8" above the 3" flange.
Both the volume and intensity of the noise is reduced inside the boat (I have insulated motor box so most of my sound comes from the back). You hear more of the motor thrum and not so much of that slapping type sound you hear from each bank firing. Conversations are easier when underway.
The biggest change is behind the boat though. I never paid attention to or realized how loud my boat is, especially on holeshot, until I couldn't hear it. I haven't stood on shore to hear how it sounds but presumably if I'm not hearing the boat as the skier, people on shore aren't being treated to the V8 symphony like they were before either.
There is no exhaust restriction with this modification and nothing is dragging in the water. There are no additional baffles. My WOT RPM with these was actually almost 100 RPM higher than without (different days). Top speed was slightly better than previous run.
The only thing to be careful of when installing is to make sure you don't push the elbows up tight to the hull if you're leaving your flappers in (I did to protect against inrushing water but you could probably remove them). Give those enough clearance to do their job.
Next step is for me to clean these up a bit and take them from POC to Production quality. I need to shave the port tip a tiny bit as it was very slightly dragging and making a small spray. There was no impact to wake quality. Wake still excellent at the 28 and 32 off I skied yesterday.
boats are like girlfriends you love them however there is another one around the corner - bananaron, July 21, 2020
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No one lives on the lake where the course is, but if less noise in the boat, I'm for it. Also, like a snorkel, I'm sure there is a Co2 benefit when surfing.
Very cool
The FA is definitely quieter than another friend’s malibu chrome turn downs on a Response barefooter.
Same crappy skier, same exact passenger and fuel load.
https://photos.app.goo.gl/iqV9Vbg3kpXPbaAAA
@vtmecheng yeah, I thought of that. I have them pretty tight. I'm about 250 lbs and leaning against them, can't yank them off right now. But I'm going to glue also. Or maybe through-bolt.
reminds me of a friends 74-75ish nautique decades back, it had these bulbous fiberglass covers over the exhaust ports, but were fastened to the transom, These did a similar function, open at bottom and very effective. Each had a 1/4" vent hole on top that shot water up and out about 15-20' feet upon startup, when the mufflers emptied forcibly.
Since your outlets are also below waterline when not moving, Consider drilling a small 1/8-3/16" vent on top of the elbow, this way after a hot shutdown the exhaust doesn't contract and suck only water back in, this would permit some air to fill voids in the muffler and manifolds, and not be all water, for multiple benefits regarding longevity and hydrolock. There has to be a good reason thru hulls have been waterline for a hundred years, else have auxiliary venting . I suspect to keep the water in the mufflers consistently at the waterline, and not creep up the riser
a strip of cheap 'chinesium seadeck' EVA nonslip under that hard fiberglass platform could further attenuate the exhaust noise reverberating between the waterline and platform, thus even less sound may propagate outward.
You may say "but the outlet is above the U/S hull line at speed", It would only take a split second at 36+mph to hydrolock the engine, another occurrence would be when going over another wake may change the boat angle and again put the open face into the water flow. The third phase I can think of is where there is a transition phase between stopped and fast enough so they are clear where the hull is inclined upward so the flat face would be facing forward into the water flow.
Not to put a downer on it as I have thought of doing it to mine, but maybe a safer option would be to use a 45deg or 60deg fitting rather than a 90deg so at least the risk of flow reversal is pretty much eliminated. It would also aid with backwash up the mufflers without a flapper due to the angle
Will report back after a year or so. 😁