Neighbor-friendly dawn patrol exhaust modification

[UWSkier]

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.

 

 

[TustinTom]

Very interesting. I never realized how loud (in comparison) our 06 LXi is until on the dock watching, then listening back to back with another boat.

 

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

[UWSkier]

IDK about the CO benefit. At surf speeds they would be in the water but just barely and the bubbles would probably be rising in front of you. The fresh air exhaust systems put the exhaust into the prop wash so it gets blasted out behind the surfer.

[skibrain]

@UWSkier well done. I'm all for mods that help with public water PR and it looks like your solution is super affordable. The Malibus are obnoxiously LOUD from the rear all the way down the lake. (I helped my buddy install a FA system on his '04 Lxi.)

[vernonreeve]

@skibrain Did your buddy like the FA system. Was the rooster tail noticeable to the skier and/or performance?

[UWSkier]

@skibrain the older ones definitely are loud without the quiet option nobody opted for. I have a buddy who tried FAE on his late model prostar 190. He said tracking and top end both suffered so he removed. Curious how it worked on the LXi

[skibrain]

@vernonreeve @UWSkier we didn’t notice any difference in ski wake up through -35 off/34mph. There is a pretty wicked shin/knee-height rooster of spray when doing a tight turn at the end of the lake @-32 and -35 as the back of a DD boat is kind of sliding that oval exhaust a skeg more sideways through water. Skier jus stays inside or goes a bit wider and not an issue really. Top speed? maybe - 1 or -2 but who skis at 43 mph? No regrets but it would be really interesting to compare with your diy.

 

The FA is definitely quieter than another friend’s malibu chrome turn downs on a Response barefooter.

[UWSkier]

Oh, no question the FAE will be quieter. Mine is firing downward as close to the water as possible but there's still an air gap. It's just shooting the sound downward rather than projecting it straight out the back like two cannons.

[WoodySkier]

One of the regulars on our lake has a 2005? response and it’s very loud in comparison to the other boats on our lake (SN196, SN200, Prostar 190). I’ll send this over to him.

[UWSkier]

So this video edit is with and without. You can hear a difference in the sound quality a tiny bit, but with the camera mounted on a metal pole right in front of the engine, most of the sound it picks up is from the engine itself. There's a noticeable difference in the boat at human head level in terms of sound harshness even if volume is only slightly lowered. But as I said in the OP, the biggest difference is outside the boat. Shooting the sound straight down seems to diffuse it.

 

Same crappy skier, same exact passenger and fuel load.

 

https://photos.app.goo.gl/iqV9Vbg3kpXPbaAAA

 

[Deke]

@UWSkier what is the difference between your setup and the chrome turn down exhausts that I have heard about? Do they both accomplish the same thing?

[UWSkier]

@Deke I've not tried the chrome tips but concept is the same. I know the chrome tips have an additional baffle as well but they're way more expensive. My setup extends down closer to the water considerably further than the chrome tips. My goal is to have them just skimming the surface at slalom speeds.

[UWSkier]

Found a video from last year where I was wearing my action camera. Replicated this morning. Can really tell the difference here.

 

 

 

[Edmund]

That is quite a difference.

[ToddF]

I like the idea, I wonder how long it will stay on with aggressive accel and decel /tight turns. it falling off every couple weeks would be my only concern.

[UWSkier]

so far so good with a few power turns today (intentionally abusing) and about 40 total holeshots since installing. I do think periodic tightening might be smart as the rubber ages. I may actually put some silicone-based adhesive on them and reinstall actually.

[BraceMaker]

Have you attempted to flatten them at all?

[Sethro]

It’s interesting to hear the models that others consider loud. Just for comparison sake, my 1998 Echelon is the quietest of our group of boats. It has the Primex mufflers (I think) from back in the day....though I’m sure the baffles are shot by now. Followed by In order of loudness: 2012 TXI, 2011 LXI, 2006 LXI, and then the obnoxiously loud 2008 MC prostar. It’s unreal how loud that boat is.

[UWSkier]

@BraceMaker I did grind them a bit flatter. Still just a tiny bit of spray off the port tip due to prop rotation. Might take that one up another 1/8" but it's not impacting anything how it is now.

[vtmecheng]

I'm always a fan of low cost solutions. My one concern is if one falls off while skiing. Never fun hitting something in the water.

[ToddF]

@UWSkier silicone is a good idea, that should help keep it in place.

[UWSkier]

@ToddF yep. I figure that should hold, and if I ever remove, I should be able to scrape any remnants off easily enough.

 

@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.

[DW]

@UWSkier - safety wire would be another option for retention.

[vtmecheng]

I think you would be surprised at how much force they have to resist when the boat is moving. Wonder if you can strap that GoPro to the back of the boat to see if they are bending up.

[ReallyGottaSki]

kewl, very effective!

 

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.

[chrislandy]

My main concern would be water being forced back up the exhaust when at speed, or at least trying to stall the exhaust water flow, causing a backup.

 

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

[UWSkier]

I'm not worried about it. Guys have been building systems for exhaust to be under water for years. Keep in mind there is a strong venturi effect here as well. Any water flowing past the opening will create a vacuum condition inside the exhaust system all else being equal.

 

Will report back after a year or so. ?

[vtmecheng]

Hydrolock is usually caused by sucking water in through the intake. For water to get all the way up the manifolds, past valves, and into the cylinders it would have to overcome a whole lot of pressure. Worst case is the engine would feel some back pressure and power would be reduced.

[ReallyGottaSki]

A more common source of hydrolock is after an impeller failure. Upon shutdown the irregularly hot steam in the mufflers and manifolds eventually cools, contracts, and pulls water up over the risers and runs down into the cylinders, a couple will have open exhaust valves.

[BraceMaker]

@UWSkier I was thinking heat gun and a vice.

[UWSkier]

I see. Haven't tried that yet.

[ReallyGottaSki]

@UWSkier i've built upon your idea and execution last week, with similar success it appears. two sessions so far without issue.

People have already offered and remarked it is quieter without being asked.

I wanted to do something because we begin and end our 6am sets in front of the same houses each day, for four months, and like yourself wanted to get ahead of any 'complaints', or worse.

In-boat is better as well. Behind the boat is substantial reduction. the spray is making more noise than the exhaust now. Albiet my boat has stock mufflers to begin with, this took it to a new level.

 

These reinforced silicon hose bends, made for people connecting turbos and intercoolers.

I wish they were a little longer, or at least as pictured, as i could really get more flush with the water flow off the bottom. They are cheap enough to keep trying.

 

Cut with some tin snips, these actually came with 2 stainless t-bolt clamps. Now i have extra clamps.

Removed the flappers, and drilled the silicon to make a vacuum break and permit air into the mufflers and risers at shutdown, especially to inhibit hydrolock if ever an overheat/ loss of raw water flow occurred.

 

I think the inherent flex of these will conform to irregular hydraulic forces that are difficult to predict, and keep them attached.

 

These 3" to 4" 45 bends, even came with ss tbolt clamps, were only about 20 bucks per side from the zon.

 

I've ordered some 4.5" 45's for my buddys boat that has the 3" internal flappers, we'll see how they fit and work. Trying to get at least half the outlet beyond that boat's cav plate, which confounded things otherwise a 90 would work well and effective i suspect.

 

 

[shufflehuff]

@ReallyGottaSki Really appreciate the post. What model boat are you putting this on? I would like a solution like this for my Response LXI.

[ReallyGottaSki]

@shufflehuff , cool. '82 supreme pictured, and the other will be a '94 centurion lapoint we still have to sort out, but likely more resembles yours and Matt's than mine

[UWSkier]

Mine are still working great. A friend put some on his TXi this spring with similar effect. Very noticeable drop in sound from the boat, especially on the holeshot when they're mostly underwater. If you're cutting them properly and cinching them down well, you don't need to worry about hydro forces yanking them off. I've used mine in water temps from 55f to 90f and no issues with contraction either. I didn't ever get around to applying silicone. I just check the tightness of the hose clamps every few months.

[hammerski]

We used to cut a small v on the trailing edge to relieve pressure build up ??

[Deke]

@UWSkier and @ReallyGottaSki are you guys drilling a vent hole in these?

 

Also, @hammerski can you explain the small V a little more? I can't picture it and don't understand which pressure it deals with. Water being forced up pipe or water being sucked up pipe?

[UWSkier]

No holes. My boat still has working flappers.

[ReallyGottaSki]

@Deke In my case yes, placed a 3/6" hole on the highest spot.

 

If i could have gotten the trailing edge on mine flush with the extrapolated line of the hull bottom, i would cut some slits so it molds to the flow without distorting, like @hammerski described . Wish i could however it seems these rarely have as much extra material as pictured, my trailing edge is definitely out of the water flow and in the air and inch or so . I may play with some 90's before summer is out, cheap enough.

[ReallyGottaSki]

Just to follow through, here is a image of 4.5" 45 degree elbows trimmed to the cav plate, mounted to internal flapper 3" exhaust. confirming very effective at all speeds encountered so far. small 3/16" vent hole drilled in top.

 

 

[Edmund]

@ReallyGottaSki Did you keep the flappers in place or take them off?

[ReallyGottaSki]

@Edmund , in the case above, the internal flappers were maintained.

 

 

Appears a lot going on...seems the flexible silicon absorbs some sound energy, as well as a modest expansion chamber to reduce the velocity of the pulse, then the water exiting with it further absorbs energy, and the aim downward reduces wave propagation along the water surface.

 

Below are some 3-3.5" 45 degree reducer/expansion elbows, yesterday i replaced my prior experiment with these.

got a nice clean cut with fresh utility knife

 

 

 

Appears the natural flex of the material makes the outlet variable in location in the z plane, , depending upon the running surface's attitude, as well as to the exhaust and water cfm as engine loading changes.

[Edmund]

@ReallyGottaSki Where did you purchased the elbow in your last photo? I am very interested in this setup as well since we have been skiing almost every morning this summer. While our course is in a cove with no houses, at one end we have to turn around in the rather narrow main lake in front of the same houses. I want to get ahead of any possible noise complaints. [There is already a current uproar on our lake about surf boats and their huge wakes.] I will take some measurements on my 1998 SNOB exhaust, and would like something to just clamp on without removing the flap if possible.

[ReallyGottaSki]

@Edmund , you must mean the 4.5" blue ones? that was these, but sold out now

https://www.amazon.com/gp/product/B017BDKTIG. there were only a couple left when i got them

 

but, suspect these or something equivalent will work well too

https://www.amazon.com/dp/B083S8H9DD/ref=cm_sw_em_r_mt_dp_U_cnWfFbENYC819

 

yes measure twice and see what you have to work with there..

 

 

 

[DavidN]

I love quiet boats!

Wish I could fabricate something similar to fit my SN 200.

Unfortunately the hull design beneath the single exhaust tip and that clamped on flapper that is mounted on the outside of the through hull exhaust pipe doesn’t allow for it. :(

 

 

[Garn]

What is the purpose of the flappers? My Moomba has flappers that attach to the outside of the exhaust rather than the inside. So if I was to do something like this I would have to take my flappers off. What would happen then?

[DW]

The flapper is a one way valve, allows water to exit and stops it from entering. the reason is to keep water from flowing back up the exhaust pipe and potentially entering the combustion chamber during a backwash event. It also serves as a very effective sound deadening device.

[ReallyGottaSki]

@DavidN I suspect one could rotate it bit to port in your case. A straight-on photo would confirm. Were really not stuffing the exhaust into the water like an FAE, just taking away the megaphone effect by aiming it downward, and directing that remaining energy going into the water first. Also, my boat has the 3" external flappers, like your 4", and those are off now ( don't have a lift so pictures are absent)

[scorban2]

My 97 SN had a 45 degree turn down mounted on it when I bought it, without the flapper. Its not perfect, but the turn down is going to prevent water from being pushed up the tube like it would with a straight exit. Ive had no issues but don't spend excessive time in reverse either.

 

[ReallyGottaSki]

@Garn, just as DW sez, along the way backwash pushing water up over the riser was identified in some cases. Flappers on vintage boats are rare, and around early seventies became standard on everything. And when one goes missing, its immediately apparent to the ears.

 

I can report this so far

Sunday it was tied up stern out, getting hammered by waves

My boat has ss commander log manifolds that have zero rise in the risers, so running worse case. No issue encountered. I suspect the wave energy is not concentrated up the exhaust nearly as much as an open outlet slapping waves squarely.

if any evidence occurs otherwise, i'll certainly report it here