I/O noise abatement..loud at WOT

[dragginanchor]

Anyone try to muffle the noise of an I/O?
It's not bad at 3500 RPM, where I like to just cruise around the lake at about 23 MPH, but at 5200 and 43 MPH it's loud enough so you have to holler to the passengers.

How about fiberglass insulation or carpet in the engine compartment??
Better engine mounts?

Exhaust is quiet with drive tilted down, so thats not the problem.

Any help with toning it down??

1750 bayliner 2.3OMC bowrider

 

[KD4UPL]

Re: I/O noise abatement..loud at WOT

I don't know if fiberglass or carpet are very good ideas. When they get wet they will be heavy and deteriorate. I've thought about using a product called Dynamat. It is typically used by car stereo installers inside of car doors and truck lids to quiet down the car. I think it would probably work around a boat engine compartment. I haven't tried it on my boat yet because I have too many other projects competing for time and money.

 

[LX Kid]

Re: I/O noise abatement..loud at WOT

I have an older 1982 Mercruiser I/O and don't know much about OMC. Is noise an inherant problem with them. What sort of noise is it? Mechanical gears, drive shaft u-joints, etc.

Oooops! Just re-read your post and I'm guessing your about engine noise at higher rpms. What about some thick bodied sound proofing sprays? Auto industry also uses thick sound deadning matting that could be cut and epoxyed to the cowling.

Another thought about the noise. Is it carb breather noise that your hearing?

 

[dragginanchor]

Re: I/O noise abatement..loud at WOT

Hey- good ideas on the materials guys..
I think it might be air intake noise LX Kid. It's got nothing but a spark arrestor on the carb. I know from experience carburetors or F/I intakes are loud without the stock air cleaner assembly. My car has a "muffler/resonator" on the intake, remove it and it growls.
Heres what it sounds like-
http://www.youtube.com/watch?v=VeNMY7O9Y8Y

Well now that I know where the noise is coming from, I might be able to muffle it somewhat..

 

[relocyo]

Re: I/O noise abatement..loud at WOT

After installing alot of loud stereos in various cars when I was younger I can vouch for the dynamat, its great stuff! And ive seen it used in engine bays on cars before so as long as you get the "pro" model stuff (looks like shiney aluminium foil) I dont think heat would be an issue, just make sure wherever you put it you want it there for good! Stuff is a real bear to get off once its on good, not terribly expensive either...

 

[Silverbullet555]

Re: I/O noise abatement..loud at WOT

You can try the dynamat, but I don't know you will get the results you want. There are too many openings in the engine compartment that let noise out and air in. Most I/Os that I have been in are the same way. At cruise, you can talk. At WOT, there is too much engine and wind noise.

 

[rallyart]

Re: I/O noise abatement..loud at WOT

There are two aspects to noise abatement. One is stopping noise from travelling through a substance and the other is stopping noise from bouncing around (absorbing it) You need a 'dead' mass to stop noise from travelling through a surface and that's where things like Dynamat and sound dampening coatings come in. That will help.
Inside many engine compartments is a foam layer that should be designed to stop the sound from bouncing off the surface and travelling somewhere else. It does not stop sound from travelling through the surface. It does help keep the sound from bouncing out through all the openings.
Any crack, vent, or hole will transmit a lot of noise out. Ensure you have these closed as much as you can but make sure you do not close off the engine's ability to breath and ventilate the engine compartment and bilge.
Good luck.

 

[scoutabout]

Re: I/O noise abatement..loud at WOT

draggin - that didn't sound too loud to me at all, but I guess coming out of my tiny laptop speakers it isn't terribly realistic.

Volume aside, though, the tone to me just sounds like the growl from a relatively small displacement engine working hard at WOT - not intake noise. My Merc 3.0 I/O sounded kind of like that but I had much more outdrive whine from the Mercruiser setup that you appear to have.

Now, whether you can muffle that any more than you have I'm not sure. Definitely make sure that anything you introduce to the motor compartment has fire retardant properties, though.

Good luck. Myself - I like the noise that motor makes, although I can appreciate the problems conversing. My damn Yamaha 4 stroke outboard is so quiet I miss the mechanical symphony sometimes!

 

[relocyo]

Re: I/O noise abatement..loud at WOT

draggin - that didn't sound too loud to me at all, but I guess coming out of my tiny laptop speakers it isn't terribly realistic.

Volume aside, though, the tone to me just sounds like the growl from a relatively small displacement engine working hard at WOT - not intake noise. My Merc 3.0 I/O sounded kind of like that but I had much more outdrive whine from the Mercruiser setup that you appear to have.

Now, whether you can muffle that any more than you have I'm not sure. Definitely make sure that anything you introduce to the motor compartment has fire retardant properties, though.

Good luck. Myself - I like the noise that motor makes, although I can appreciate the problems conversing. My damn Yamaha 4 stroke outboard is so quiet I miss the mechanical symphony sometimes!

Yes, the WOT silence is some of the best to get... I also enjoy such symphonies

 

[user64]

Re: I/O noise abatement..loud at WOT

They do make kits specifically for i/o's that fit under the doghouse and they are fire retardant. I had installed one and it did cut down the noise. (cant remember the name, sorry). As rallyart said , you have to cover every hole. Venting is not an issue because you are pulling air into your boat thru those side vents and it is fed up from the bilge to your engine. The kit does not obstruct that...merely adds an inch or so of sound deadener to the top and sides of your doghouse. Good luck.

 

[relocyo]

Re: I/O noise abatement..loud at WOT

You can try the dynamat, but I don't know you will get the results you want. There are too many openings in the engine compartment that let noise out and air in. Most I/Os that I have been in are the same way. At cruise, you can talk. At WOT, there is too much engine and wind noise.

I think thats debatable on pure regards to application... I believe I could cover said holes in engine compartment on numerous doghouses.... Just sayin

 

[25thmustang]

Re: I/O noise abatement..loud at WOT

I don't hear anything out of the ordinary in the video. My boat with inboards is the same way. Push motors up to 4000+ RPM and they tend to make a good amount of noise.

 

[H20Rat]

Re: I/O noise abatement..loud at WOT

The engine from the noise is causing the wood panels to vibrate, and that in turn causes noise outside. Noise generally doesn't travel well through a rigid piece of material, it turns it into a speaker by causing it to vibrate and re-transmit the noise instead.

Anyway, foam absorbs sound, in particular higher frequencies. Mass loaded vinyl and stuff like the commonly known dynamic absorb some low frequency sound, but it also makes whatever it is stuck to heavier, and turns it into a less effective speaker for transmitting sound. (it lowers the resonance frequency, so even if it still vibrates, it won't be as annoying or noticeable.) For the best sound deadening, you absolutely need both.

(years of car audio competition experience... My current car has at minimum one layer of raammat on every single interior metal panel, followed by one layer of ensolite (foam). In critical areas it is multiple layers. Obviously raammat/ensolite is what I use, its more effective than dynamat and cheaper too!)

http://www.raamaudio.com/