anyone know how to quiet a two stroke.

[amk]

anyone got any tips on how to quiet the noise from these jet ski engines were putting in. My 760 is loud enough I now need to wear ear plugs if I'm going to run wot for a hour. Im seriously considering spray foaming my resonator box and exhaust lines. Any other ideas?

 

[DaleH]

There is a special paint to absorb vibration and frequency-driven noise, plus there are lead-lined foam/foil sheets to quiet down engine rooms. See Sound Down Engineering.

Google 'noise absorbing paint' or 'noise absorbant lead lined foam'

See: https://www.soundown.com/AI.htm

 

[bnt5]

did you put the exhaust in the water? mine isnt loud at all no different than an outboard.

 

[CedarRiverScooter]

PSG-1 has a good concept regarding an exhaust curtain. It's somewhere in his build thread.

 

[JL8Jeff]

When I modified the Yamaha 650 in my old Boston Whaler Rage, it got pretty loud so I added a water injected silencer. I put a tee going into it and a valve so I could adjust how much water went in. It made a big difference in the sound level and didn't seem to affect the power output.

 

[DaleH]

Good info from those w/ jets ... I was curious if one could make it a totally underwater exhaust like they do on diesel boats???

 

[CedarRiverScooter]

Maybe not totally relevant, but on my inboard ski boat i installed a 'Fresh Air Exhaust', which is a duct that sticks down below the waterline. It's main purpose is to direct fumes away from the passengers, but obviously makes the boat very quiet. It actually improves fuel economy at mid range RPM, which is where I operate most of te time.

If you want some thing to copy, check out 'FAE' website.

 

[PSG-1]

Install a rear platform on your boat, this will help quite a bit. But the most effective way is to route the exhaust flange where it goes right into the side of the jet, then install rubber skirting. Take a look at a Yamaha VX110 to get an idea of what I'm talking about.

Also, get some (fire-retardant) "egg crate" style foam, install it in the engine compartment. A good bit of noise comes from the engine, as well as the exhaust. Every little bit of sound-deadening helps 8)

 

[CedarRiverScooter]

AMK - Did you get your boat quieted down?

I recently wrapped the exhaust system of mine with leftover I/O carpet & it made a big difference. Not fireproof but neither is the plastic cover of the carb intake.

 

[BassAddict]

I just use more lotion....

 

[PSG-1]

Here's a few pics of the exhaust baffle system on my boat:


In the upper left corner inside the tunnel is where the exhaust exits



Along the inside edge of the tunnel is a flange, where the rubber skirting attaches



Rubber skirting is notched to fit around the jet nozzle, including notches for the steering cable and hoses



Here it is with one side of the skirting attached. Once both pieces are installed, and then the ride plate is underneath, sound signature is greatly reduced.

 

[tigfisher]

my exhaust comes out of side of the hull, underwater when sitting still. when the water box fills up with water from the pump it quiets down a little, but the main thing that cut the noise in half was the insulation of the water box, pipe and engine comp. with fiberglass foil insulation used in home air duct insulation, lots of noise come out of the carb too

 

[PSG-1]

I just use more lotion....

You ain't right. LOL :mrgreen: :LOL2:

 

[BassAddict]

I just use more lotion....

You ain't right. LOL :mrgreen: [emoji38]2:

Believe it or not but I have been told that by numerous people..........

 

[CedarRiverScooter]

This is a dissatisfier for me also. Been going on hour+ rides, & my ears are ringing when I get back. I tried to add the skirt, but the polaris pump tunnel has obstructions making this impractical. I put a rubber 'flap' on the EXH outlet, but I think it is limiting power more than noise.

My immediate plan is to use earplugs.

Long term, I would love to find a 4 stroke engine, I think it would be easier to muffle without losing power. Been using 4 gallons of gas per hour, btw, would like to reduce that too.

So far I have run up on a gravel shoal, hit a rock & a log, - no damage to the boat!

It's a blast . . .

 

[PSG-1]

CedarRiver, does your boat have a rear platform? If not, adding one will help quiet it down a little bit.

Also, if your exhaust exits right out the transom, you might consider adding some type of chute that goes over the exhaust outlet (picture something like a chute that covers a typical household dryer duct on the outside of the house) This will direct sound toward the water that's rushing from under the edge of the transom, instead of straight out the back of the boat. You can make the chute with the bottom edge as low as you want (the lower the better), just as long as it's about an inch or two above the bottom edge of the boat, so you don't force water into the exhaust.

I ran a setup like this on my boat when it had the 2 stroke engine, and it definitely helped.

 

[Ranchero50]

This is a dissatisfier for me also. Been going on hour+ rides, & my ears are ringing when I get back. I tried to add the skirt, but the polaris pump tunnel has obstructions making this impractical. I put a rubber 'flap' on the EXH outlet, but I think it is limiting power more than noise.

My immediate plan is to use earplugs.

Long term, I would love to find a 4 stroke engine, I think it would be easier to muffle without losing power. Been using 4 gallons of gas per hour, btw, would like to reduce that too.

So far I have run up on a gravel shoal, hit a rock & a log, - no damage to the boat!

It's a blast . . .

What speed are you only using 4 gph?

This is my current exhaust setup. You can see the old discharge above the pump and it was very loud there. With the new version on the pod the exhaust is pretty quiet until I'm running hard because the port is under water. I am running the stock water muffler as well. You can get an idea from my goofing off videos of how it sounds.

As said above, a lot of my noise is from the decking vibrating at speed. I put some fuzzy velcro at the hatch openings to quiet them down. Eventually I'll install the carpet (it's only been sitting in the rafters for six years waiting) and hope it quiets everything down.

 

[CedarRiverScooter]

Thanks Ranchero for the picture. Good idea on the underwater exhaust. I have an idea on how I can try that out without cutting a hole (running a radiator hose down the outside of the transom). If it pans out, then I will make it permanent.

I have been cruising about 25 MPH, & usually use 4 gallons on the hour trip (up to the dam & back). It uses 6 + gallons if I go above 30 MPH for the same trip. The pump must lose efficiency at the higher output.

 

[brianb2247]

some skis come with water boxes that dont have the water line connection on them ,typically they are louder than the ones that do this can be a mod upgrade to quiet down yours , the other thing you can do is make an air tight engine lid over your engine then make an opening on the far front corner of it to draft fresh air across the engine and in through the intake i used a 3 inch blower cover. my engine cover is welded in and sealed with poly seam sealer from lowes and to quiet it more i rolled the behr deckover textured paint over it two coats (with a special roller) really took the pinging noise away from traveling through the aluminum. [-X do not use the restore deck paint its sand based and will burn you up in the summer heat

 

[CedarRiverScooter]

Well, I got some flexible exhaust pipe & was able to route the exhaust over the transom & down underwater. $10 total cost so far. It sticks down about an inch below hull. Made quite a difference in noise level, but you guys are right, the exh is only half the noise source. Now I can hear all the rattles, etc. The flex pipe is temporary, hopefully will come up with more elegant design next winter.

I was concerned I would get a hydrolock situation upon shutdown/restart but that didn't happen.

The only negative consequence is spray up onto the transom. Next I am going to make a shoe to hold the spray down. I'll take a picture once I get that done.