Neighbor-friendly dawn patrol exhaust modification

[DavidN]

@ReallyGottaSki - Best pic I have...

I’m still a bit wary about taking off the flap.

Would probably be fine without it, but I have to back out of my lift very time we use the boat. And the least thing I need now is a waterlogged 6 Liter engine.

My wife would kill me.

[ReallyGottaSki]

I understand David, we can hobby and eff around with our old tubs with less risk.

 

I think you would be just fine, consider if the flap was that critical, there would be a flap missing warning light. Partially in jest.

However that said, you have considerations that are more consequential with a fresh boat.

[UWSkier]

My downturns work awesome but if my boat was as quiet as a Nautique, I probably would not have bothered with this modification. Nautiques do drone a bit but the sound is less harsh with the two-into-one expansion chamber setup.

[WoodySkier]

@DavidN the Naitique 200 is already a very quiet boat, I wouldn’t touch it. The Malibu’s are notoriously loud.

[shufflehuff]

So I have one of those loud Malibu's that was referenced above. I would like to install something like what is being described in this thread. Has anyone done this on this style exhaust tip that's installed on the Malibu's? Do I have some sort of internal flap? See attached picture.

 

[DW]

@shufflehuff - if you look up inside the exhaust tip you should see a metal flapper. It serves the same anti reversion job the rubber flappers do on other style tips. They don't offer the same sound absorption as a rubber flapper.

[UWSkier]

@shufflehuff with as much material as those things have to clamp to, I'm sure you could fab up something to work well to turn the sound down. If you know a good welder, you could probably even turn those into downturns.

[ReallyGottaSki]

@shufflehuff , what size are those dale jarrett specials, 3.5" od?

[scorban2]

@shufflehuff the mounting on those tips looks very similar to the ones on the new Prostar, but the Prostar tips have a turndown. Maybe you could contact Mastercraft or find the supplier to see if the turn down version would bolt up to your boat.

[UWSkier]

Malibu offers those down-turns too. The problem with replacing them is it's a pain. Need to pull the fuel tank, couch, trunk, etc.

[DavidN]

@shufflehuff

I had the exact same exhaust tips on my 2005 and my 2006 Response.

They look way cool, but are indeed pretty loud.

Surprisingly they have no internal flappers whatsoever.

When I took delivery of the 2005 Response (my first ski boat) I had the dealer check back with Malibu and verify that I won’t run into any issues with these tips w/o flappers. Malibu assured him that I would be fine because of the exhaust silencer setup that would prevent any backflow.

 

These tips will be ideal to clamp on the silicone elbows shown by @ReallyGottaSki above. If I remember correctly, they are 3.5” outside diameter.

 

[ReallyGottaSki]

After some browsing, this could be e a good 3.5" solution

But i would check the clamps after a week or two, the chinesium clamps may not be stainless on all its hardware, may just be the band...then source some quality clamps locally.

but, a modest 50 dollar experiment...

I must reiterate drilling a vent hole at the top, it will maintain the water level in the exhaust the same level it was always at after shutdown.

 

https://www.amazon.com/dp/B07VCMS69P/ref=cm_sw_em_r_mt_dp_U_JdhgFb38YJH77

[DavidN]

I decided to give it a shot and fabricated a custom turn down tip for my SN 200.

I used a 4 Inch ID silicone 4-ply 90° elbow, cut it to fit, removed the flapper and used the existing stainless worm clamp to fasten it to the through hull fitting.

So far so good, but I might have cut it down too much.

It is a lot quieter at idle and for the first 10 feet of acceleration but when on plane and at skiing speed, there’s not much of a difference.

What I really like is that it completely eliminated that obnoxious, explosive, water goshing loud roar at start-up.

 

 

I already ordered another elbow which I will cut flush with the hull.

 

Pretty sure my neighbors at both ends of the slalom course will appreciate our boat being even quieter. :)

[ReallyGottaSki]

David, good to hear its working for you

its vented at the top, yes?

[UWSkier]

Inside the boat, the difference isn't huge, but stand on the dock and have someone drive away from you both with it, then without it. That's where the difference lies. You don't want to be flush with the hull. Maybe 1/4" above.

 

Not sure I'm crazy about the idea of eliminating the flapper though.

[DavidN]

@ReallyGottaSki

Yes, I put a 1/4” vent hole in the silicone coupler. It’s on the top of the elbow. However, I don’t really see the point of it. My last Malibu had stainless turn down tips without holes, so I might skip that on the next try.

 

 

@UWSkier

Ok, will cut it slightly above flush, but this time straight, not angled upwards like the first try. (I can always cut more off if it drags.)

 

I thought I’ll do it similar to these tips:

 

And yes, I’m wary about losing the flapper as well, but none of my previous DD boats had flappers in the tips or inside the exhaust, first 2 Malibus had straight tips, last one the turn downs. None of them had internal flappers, so I think I should be fine without it.

[UWSkier]

@DavidN I thought those had internal baffles to help slow any inrushing water.

[DavidN]

@UWSkier

Of the turn downs (AKA silent rider tips) some had, some not. Mine came without any internals. And the straight pipes (shown here on page 2 by shufflehuff) had no internals either. I had two boats with these tips. Great looks, terrible loud.

 

Here is a picture of the silent riders:

And here’s mine:

As you can see - Empty inside! :o

 

[DavidN]

Little follow up on my exhaust mod...

 

Yesterday I was just IN the boat, pulling my wife a set at 51k and already noticed the boat sounded a little different and was a bit quieter from the inside.

 

Today I was BEHIND the boat and took a set at 55k and WOW it definitely is quieter back there now!

When behind the boat in the water you only hear a faint low V8 rumble and more of a bubbling sound from under the swim step. When skiing I was barely able to hear the engine at all. :o The sound of water splashing and goshing around me and the wind in my ears was more prominent than anything else.

 

I will still try a modified version of the turn down (cut a bit lower and more in line with the hull) but I’m really happy with how it turned out so far!

[UWSkier]

@DavidN First time I got pulled up behind my boat with this mod, I realized just how much engine noise I had before. The video I posted on Page 1 is really indicative of what it's like.

[MNshortliner]

Did this tonight. Thanks for all the tips/how to posts. The rubber is the 4” clay to 4” pipe. And the white pvc is 4” to 3” elbows. I cut off the flange that the 3” pvc pipe would go into and it makes for a fairly clean sweeping 90* turn. And just about the right clearance above the water.

Right now I only have it clamped with the 2 hose clamps on each side but the rubber fitting took a little tapping and stretching to slide on my stock exhaust ports with flappers. I made sure the flappers still open 3/4 of the way. But for $10 per piece it is a great and easy mod. $40 all in. I did drill a 3/16” relief hole in the top of the 90.

First impressions of it: From the boat hard to say if it is quieter or not. From a skiers perspective it was way quieter. I’m sure from shore it has to be a big difference.

 

 

 

 

[DavidN]

@MNshortliner

Think you got a typo above.

Isn’t the outside diameter of your exhausts ports 5” rather than 4”?

If so ... below silicone elbow would make for a little nicer looking mod.

Plus the advantages that @ReallyGottaSki mentioned earlier.

 

https://www.intakehoses.com/silicone-90-degree-reducing-elbow-5-to-4-id-gloss-black.html

 

And I’m pretty sure you could cut them a tad bit closer to your bottom hull line.

 

P.S.

My mod 2.0 works great.

A neighbor (another skier on my lake) mentioned the other day that he was astonished by how quiet my boat was. :)

[MNshortliner]

@DavidN you are correct the O.D. of the stock exhaust ports are close to 5 1/2”. The rubber fitting are made for the clay pipe that has 1” thick walls. The sticker on it said 4”x4”.

It is a clay pipe to pvc coupling. I was pretty happy with how much to tamed down the exhaust but I will check it out again tomorrow.

[rockdog]

Why don't they come like this from factory I'm wondering? This seems like such a good idea. There has to be a reason?

[UWSkier]

@MNshortliner interesting that your Response exhaust outlets appear to be cut a bit higher than on my '01 with the same hull. Must have been a different jig for the guy with the hole saw. :)

[shufflehuff]

So I have posted on this thread a couple of times regarding this modification to my Malibu Response LXI. This Response LXI has factory straight exhaust tips. The tips nor the mufflers have any kind of flapper installed. I ordered a set of 45 degree elbows. I wanted to get the groups opinion before I move forward. I am wondering if I should try 90 degree elbows instead. Any opinions on what I should do from someone who has had success with this modification? See pictures below.

 

 

[UWSkier]

Fit looks great but think you'll get more benefit from properly trimmed 90s.

[DavidN]

Agree with @UWSkier, however as you already have the 45’s, cut them 1/4” above hull and give it a try. You might be surprised. Will definitely be an improvement over the straight pipes!

 

 

[ReallyGottaSki]

I concur, trim just above the running surface.

Seems 90s may be more effective for you but you should get some attenuation with those 45s, give them a go

Too bad they don't give a little more material to work with.

[Deke]

For you guys that have done this, what are your thoughts regarding temperature about using EDPM fittings instead of silicone? I found 5.5" 90's that would fit the more current Malibu flappers but only in rubber. Here's the link...

[ReallyGottaSki]

@Deke there could be slightly less attenuation with those vs silicon but its good for a test.

Temp rating is markedly less, but also since there is always water present not HP steam, it wont see more that 212F, And if it does, you have bigger problems going on.

It may conform less to irregular water off the running surface, but no different than other methods already demonstrated

 

Still, vent the top so the water in the mufflers stays the same historical level under all conditions else the system will want to breathe through the engine at rest.

[chrislandy]

Has anyone actually measured the reduction?

 

2 weeks ago I measured mine at 105db out the back and 95db in the drivers seat. I remade by original silentmaster silencers on the 205, after the impeller went a couple of years ago they melted internally and I'd been running twin 3.5" straight through.

 

Put the two underfloor silentmasters back in, bitumen type sound deadening directly on the inside face of the motorbox, with a second layer of 1" acoustic foam. Now it's 60db in the drivers seat and 65db on the back. It's that quiet you can talk (loudly) to the skier and hear their reply and talk normally to someone in the back seat. That's running 16-20mph for the kids and 32mph for me.

 

In fact the wife didn't realise the boat was idling at the dock the first time out!

 

 

So how quiet do you want/need it?

[Deke]

I remade by original silentmaster silencers on the 205

@chrislandy what does that mean? Are these rebuildable? I have Silent Riders on my '99 RLX but they're still pretty loud out the back.

[chrislandy]

typo, I remade my ones. i.e. spent a day hacking and cutting out the sealant around the end caps. Cleaned out the tubes, re-glassed the bits that had melted/broken off and stuck it all back together again. It's only fibreglass and not even high tech so pretty simple to rebuild.

Mine has the two separate silentmasters horizontally under the rear floor then straight out (twin 3.5") with rubber flappers rather than the single across the back silencer

[ReallyGottaSki]

@chrislandy those are some remarkable attenuation numbers!

 

I'm at a level at ski speeds where one doesn't have to raise voices also, and it's nice for everyone

 

I have procured similar foam for the engine cover yet to install, it may be next season as I also need to glass some screw holes that don't grab any more

 

I'll play with the db meter tomorrow to get a benchmark

 

 

[chrislandy]

 

For those interested (and capable) of working with fibreglass, this is how you "could" build the silencer, if made longer you could also add more baffles internally.

 

 

These are the insulation materials I used:

https://www.carinsulation.co.uk/product/marine-engine-compartment-insulation-glassmat-hr

 

https://www.dodomat.com/products/dodo-dead-mat-hex-roll

 

the biggest difference I noticed was from the engine bay double insulation

 

 

 

[DW]

@chrislandy - impressive. Did you measure how much added weight the insulation added?

[Deke]

@DW I did my motorbox with a 1" composite foam a lot of years ago so I don't have exact numbers. I think I bought close to 100 pounds and probably used 80% of it though. (!)

 

It's pretty quiet inside the boat.

[Andre]

80 pounds of insulation foam in the motorbox????????????

I did mine with 1'' foam from McmasterCarr.Can't be more then a couples of lbs...

[Deke]

Yeah, @Andre this is heavy stuff. I don't remember how much was used but maybe as little as 60. It is not your everyday foam. It is a specialized acoustical foam. Lot's more attenuation but admittedly I didn't realize how heavy it was until I received it. You definitely don't want to drop the lid on your foot!

[Edmund]

@Andre Exactly which product did you get from McMaster-Carr? I would think it was a high temperature foam. I really would like for my motorbox to be quieter.

[chrislandy]

@DW somewhere around 12-14kg (26-30lb) for both, the 1" foam is around 2lb/m2 and the bitumastic one is around 8lb/m2

 

I doubled up some areas where I thought more sound might come from (pully area at the front of the box, the perimeter around the bottom and a little extra behind the driver)

[MNshortliner]

Do any of you have a pic of your finished insulation project?

[Deke]

@MNshortliner unfortunately I do not have any photos. I'll try to get some next week when I get back to the lake. I did this in 2007. After making templates and cutting, the pieces were hung with a combination of a 3M 90 spray adhesive and epoxied-on spikes with caps and washers. Edges were covered with heavy self adhesive HVAC foil tape. Also, had to be sure that the vent at the rear of the box was kept open. I did not insulate the floor over the muffler compartment.

[Andre]

@Edmund

Been a while but good info in this thread...

http://www.mastercraft.com/teamtalk/showthread.php?t=30120&highlight=insulation

[MNshortliner]

@Andre Thanks for the link. Lot of good stuff in that thread and I will have to read all of that one later. Just more curious on what you guys were doing. I feel that most my noise comes from the exhaust and I don’t hear much from the engine. I will have to look and see what is under my dog house.

[shufflehuff]

So I have been working on a solution for my Malibu Response LXI. I have made a couple of post here on this thread about it. Back on page 3 I showed that the 45 degree bend didn't seem like it was going to work very well on my setup. I ordered a set of cheap eBay 90 degree elbows. Unfortunately the "leg length" was not long enough to cover up the long extended straight exhaust fittings that exits the hull. I have attached a couple pictures to show this. I ended up ordering another set of 90 degree bend elbows but with longer "leg lengths". This seems to be perfect, but as you can see the elbow now hangs below the bottom of the hull.

 

I am struggling to decide where to cut the new 90 degree elbows. I saw on a previous post that some one suggested 1/4" above the bottom of the hull. Is this my best option? I really want to do this correctly one time since these were quite a bit more expensive than the eBay version I tried first. Thanks for the input.

 

 

[DavidN]

Mine is about 1/4 Inch above the running surface and I angled the cut ever so slightly upwards toward the rear to account for bow rise while getting on plane.

It works great and reduces the exhaust noise significantly even on the usually pretty tame sounding SN 200. I punched three 3/16” vent holes at about 11,12, and 1 o’clock on top of the hose as close to the existing hull fitting as possible.

I don’t think the vent holes are necessary on your setup as your original pipes are under water anyway, even when the boat is just sitting in the water. It’s a little different with the Nautique, where the original flapper sits just 3/4 under water and when killing the engine air is entering the exhaust. I wanted to keep that situation to not get water sucked up into the exhaust with the silicone elbow.

 

My advice would be to first cut the “too short” elbows little by little until you are satisfied with the result.

They bend away easily when too long which is not really a problem besides producing a little spray off the stern. (Good visible while skiing behind the boat). If they do, cut some more.

That way you’ll have a “template” where to cut the ones you intend to keep.

 

*edit*

Pro tip :D for cutting the silicone hose.

Use a new (aka sharp) box cutter. Stuff the elbow with a piece of big pool noodle, put a metal hose clamp around it, position where you want to cut and then cut in one stride along the edge of the clamp. That way you end up with the cleanest possible cut.

(I cut a few times and on 2 different silicone elbows, so I eventually came up with that trick.)

[ReallyGottaSki]

Indeed, some material has to go, else they would likely want to fold and pinch closed

 

Nice tip for a clean cut

[hammerski]

https://www.summitracing.com/parts/sch-43035