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.