Super quiet, like a 4 stroke!

[Algarve]

Yesterday I saw a 90 mercury carb 2stroke 1997, super quiet, like a 4 stroke. Does anyone have any idea how it was possible to make some noise in high gear. One more thing, the engine was working, not off.

 

[Silvertip]

Re: Super quiet, like a 4 stroke!

Look at most noise ratings for four strokes and two strokes at wide open throttle and the numbers get pretty close. Four strokes are quieter in the idle-mid rpm range. Even a carbed two stroke idles nice but once the throttle begins to open so does the noise until all things equal out at WOT

 

[Texasmark]

Re: Super quiet, like a 4 stroke!

Back in the 50's to 70's, OMC's prime competitive element with their prime contender Merc was noise. They were right and their strategy worked. OMC's were very quiet once the Merc blew past them and you could (couldn't) hear them anymore (the Mercs) they (the OMCs) were very quiet. I had both more than once so don't come back with any replies containing brand bias baloney.

4 cycle engines are quiet because the entire combustion process is water sealed whereas half the 2 cycle is dry. However, they (2 cycles) have made great strides to quiet things down and things aren't like they used to be, even though they did it and still maintained the light weight advantage over the 4 cycle engine.

Hey, back in 1963 I ran the Homelite 55 hp Bearcat. I know how quiet and smooth 4 cycles were.....now that was one beautiful engine. Problem with that engine was that it was 40 years ahead of it's time. And that pilgrims is a crying dirty shame. It happens all the time; the market sets the market and if the market is blindsided, the consumer looses and I can assure you this was surely a case for the consumer loosing big time.

You know, sales hype is just that, sales hype. Like right now we have primary elections coming up on Mar 2 and we are getting all sorts of smoke blown up our ......... The problem for the owner/potential-purchaser/buyer/voter, is separating these miles of B( )aloney..................from reality.

Good luck,

Mark

 

[4JawChuck]

Re: Super quiet, like a 4 stroke!

My 2003 90Hp Merc is very quiet compared to the 87 50HP Yamaha it replaced. Much of the difference is in the hood intake baffling and insulation inside the hood, you can replicate this with sticky backed sound insulation used in car stereo installations.

I was so surprised when we went for our first ride, even the wife couldn't believe how much quieter this motor was...we could even talk while cruising along at 4500 rpm! You can bet this summer I will be experimenting with adding more insulation into the hood pan and anywhere there is bare fiberglass, it makes a huge difference and is easy to do for the home handyman.

 

[Texasmark]

Re: Super quiet, like a 4 stroke!

My 2003 90Hp Merc is very quiet compared to the 87 50HP Yamaha it replaced. Much of the difference is in the hood intake baffling and insulation inside the hood, you can replicate this with sticky backed sound insulation used in car stereo installations.

I was so surprised when we went for our first ride, even the wife couldn't believe how much quieter this motor was...we could even talk while cruising along at 4500 rpm! You can bet this summer I will be experimenting with adding more insulation into the hood pan and anywhere there is bare fiberglass, it makes a huge difference and is easy to do for the home handyman.

d

That was the, one of the, problems with the Mercs I was referring to. With the inline design and clamshell shroud, it didn't leave much room for sound deadening innovation. I remember on one of them I owned, they made an attempt at sound deadening by adding a fiberglass blanket encapsulated in plastic around the inside of the shroud. Problem with that was that the plastic kept the sound absorbing qualities of the FG from being able to receive and inhibit the noise. It was about useless. The current practice of open cell foam inside a plastic bonnet works sooooo much better.

Mark

 

[Algarve]

Re: Super quiet, like a 4 stroke!

Much of the difference is in the hood intake baffling and insulation inside the hood, you can replicate this with sticky backed sound insulation used in car stereo installations.
I will be experimenting with adding more insulation into the hood pan and anywhere there is bare fiberglass, it makes a huge difference and is easy to do for the home handyman.

The current practice of open cell foam inside a plastic bonnet works sooooo much better. Mark

My friends
Due to the difference of our language, some words become hard to understand, but deep down there is understandable.
I have a 1997 Mercury 90hp 2stroke, very loud, but also gives more adrenaline.
I have some doubts about what they said, thank you for explaining better again.
The foam does not warm to the point of fire inside the capot?
For simplicity can put here some pictures or links to material that can reduce the sound of the engine.
Excuse my English but I am using the translator and does not always translate correctly.

 

[Texasmark]

Re: Super quiet, like a 4 stroke!

My friends
Due to the difference of our language, some words become hard to understand, but deep down there is understandable.
I have a 1997 Mercury 90hp 2stroke, very loud, but also gives more adrenaline.

The foam does not warm to the point of fire inside the capot?

Excuse my English but I am using the translator and does not always translate correctly.

I have the '02 90 which is the same engine essentially and I find it quiet considering that there are 90 ponies jumping around under the bonnet and especially quiet when compared to it's predecessors I have had over the years.

The highest temperature normally encountered anywhere on the external parts of the engine (all that is under the bonnet) would be on the order of 150F (70c more or less without looking up the conversion). You can put your hand on that for a few seconds. That is not adequate to ignite open cell foam so don't worry about a fire. Only considerations would be to allow for air flow from the rear top of the bonnet (where it enters) to the sound box (over the carbs) input holes, and allow room for the starter to work and the flywheel to spin. But nowadays they put protective covers over them so that isn't a problem like it once was.

If it is still unclear to you, ask more questions.

HTH,

Mark

 

[Algarve]

Re: Super quiet, like a 4 stroke!

Better would be impossible, thank you dear friend.
it is possible to post here a link to facilitate the understanding of what foam?
Best regards

 

[Texasmark]

Re: Super quiet, like a 4 stroke!

Better would be impossible, thank you dear friend.
it is possible to post here a link to facilitate the understanding of what foam?
Best regards

I would not hesitate to use the kind of foam you could purchase at a department store (Walmart?) in the sewing or maybe bedding department. This foam could be 2 or more inches (6 cm) thick and reasonably firm when squeezed by hand. Cut it with scissors or a razor blade/box cutter knife and install with rubber adhesive or silicon rubber RTV. The silicon may be a better idea as the chemicals in the rubber adhesive may melt the foam, not sure but might.

Do not coat the exposed foam with anything as to do so would limit it's ability to absorb sound. It may pick up a little oil from the engine (flywheel) over time but this is not an issue.....like I said there is nothing in there to start a fire.

HTH

Mark

 

[4JawChuck]

Re: Super quiet, like a 4 stroke!

This is the product I see at stores in my area, seems like everyone has it in stock. They recommend layering the reflectorized stuff over the Dynamat Extreme for the most sound proofing.

http://www.dynamat.com/products_automotive_hoodliner.html

 

[MercGuy]

Re: Super quiet, like a 4 stroke!

I have a 1998 Merc 115 carbed 2 stroke. My buddy bought a Yamaha 115 4 stroke sometime around 2001.

I always felt that my Merc was quieter than his Yammi. Part of the reason was that the Yamaha ran faster. I think his has a red line of around 6500 while my Merc redlines at 5250.

However, the Yamaha is fuel injected and starts with the flip of they key and idles without a hiccup.

I think that the myth of 2 stroke noise, much like oil burning and fouled plugs, is rooted in the past.

-Steve

 

[Algarve]

Re: Super quiet, like a 4 stroke!

You guys are fantastic. Your help and expertise are excellent.
Greetings from this side of the Atlantic.

 

[Texasmark]

Re: Super quiet, like a 4 stroke!

The material in your picture is more for heat reflection than sound. I have OEM hood liners on my trucks and they are fiberous mats with lots of surface area to trap noise just as the foam will do. They do not contain a reflective aluminum shield.

I have seen mats hung off the ceilings in noisy work environments. They were made of foam, fiberous mats and lead sheets all in a sandwich.

I think you would do best with the foam or I wouldn't have suggested it to you since it worked for me in the past.

Mark

 

[4JawChuck]

Re: Super quiet, like a 4 stroke!

Dynamat for under hood applications is not just reflectorized foil, it has a fibrous tar backing that is sticky much like the OEM stuff on vehicle floor boards. It is not that thick however hence why they recommend using it over their sound absorbing product...its mostly for absorbing vibration.

Have a look at it when your in an auto parts supplier, expensive stuff though.

 

[Algarve]

Re: Super quiet, like a 4 stroke!

Ok, I understand, but what can I use to keep the engine quieter?
Or is it better for one to absorb more vibration?

 

[Texasmark]

Re: Super quiet, like a 4 stroke!

This is my last reply. I have told you 3 times what to do and you have chosen to ignore me. Last time and here it is:

2's and 4's do the same thing to transform the BTU's of energy in the fuel to crank shaft rotations. The difference in the two processes is that 2's interrupt the explosion half way down the power stroke whereas 4's let it go all the way down and obviously the 2's do it twice as often as the 4's. Obviously, if you let it (the piston on the power stroke) go all the way down, you get more energy out of the impulse and when you interrupt it (open the exhaust valve) less energy is lingering and less noise of the explosion is remaining. So the result is quieter and since it happens half as often, it is even quieter still.

So, other than mechanical vibrations, most of your noise is associated with the exhaust manifold and mid section exhaust tubes. Add your foam under your bonnet (cowling), especially in the area of your exhaust manifold.

All I am going to say.

Mark

 

[Algarve]

Re: Super quiet, like a 4 stroke!

This is my last reply. I have told you 3 times what to do and you have chosen to ignore me. Last time and here it is:

2's and 4's do the same thing to transform the BTU's of energy in the fuel to crank shaft rotations. The difference in the two processes is that 2's interrupt the explosion half way down the power stroke whereas 4's let it go all the way down and obviously the 2's do it twice as often as the 4's. Obviously, if you let it (the piston on the power stroke) go all the way down, you get more energy out of the impulse and when you interrupt it (open the exhaust valve) less energy is lingering and less noise of the explosion is remaining. So the result is quieter and since it happens half as often, it is even quieter still.

So, other than mechanical vibrations, most of your noise is associated with the exhaust manifold and mid section exhaust tubes. Add your foam under your bonnet (cowling), especially in the area of your exhaust manifold.

All I am going to say.

Mark

Dear Mark,
Do not be angry with me because there is no need. Who does not know and who does not understand, it is not wrong to ask who in principle will know more than him. But still and all is well between sailors.
Sincerely.
Jo?o, from Algarve.