Here's the setup in question:

[IMG]http://i11.photobucket.com/albums/a180/gtofan1/PM11000-1.jpg[/IMG]

This is option A:

[IMG]http://i11.photobucket.com/albums/a180/gtofan1/193030_lg.jpg[/IMG]

This is the one I don't think will fit:
[IMG]http://i11.photobucket.com/albums/a180/gtofan1/60242L_lg.jpg[/IMG]

Sorry...

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Option A:

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Yup, those contractor grade generators can be annoying but they are less expensive than the camping versions which are whisper quiet. You get what you pay for.

Adding a length metal flex and running to a muffler or to the open can create back pressure and temperature problems for the exhaust valve and cause damage and Honda anythings aren't cheap to fix.

If you can find a gen that uses the same Honda engine with a quieter muffler that's where I'd start on the cheap.

I was in your exact situation and finally admitted to myself that I bought the wrong generator for what I needed it to do or go to war with the neighbors. Sold the generator on craigslist and bought what I should have in the first place... a smaller, yet ballsier, whisper quiet, fuel efficient Yamaha inverter generator. Honda, Yamaha, and Robin-Subaru have some really nice models that aren't insanely expensive and are highly though of. I'd avoid the Chinese knock-offs if you go shopping.

My powermate 5000 has the Subaru/Robin 10Hp and is quiet enough that my neighbors can't hear it...helps the gen is located in the back of my house and i'm set a good 150' from the road.

The newer one with the GX620 isn't much louder...but with the big flywheel fan noise and the exhaust it's barking 80db at 7 meters....the basis for measurements for these units. Problem is finding a 11KW continuous watt generator that's quiet I will need to sell my wife's car..:)

Backpressure is a concern...I don't know how much is too much with these engines..what ever I install it will surely have less or equal to what's on it...worst case only very slightly more but not likely...that cheap can on there now can't have more than the bike exhaust muffler I have laying around.

With a different muffler and a baffle in front of the fan, i'm sure it will be much quieter than my Robin engine..just need to brainstorm.

To lower sound you can muffle it or redirect it...

In some of the Powermate manuals they talk about a box as a weather enclosure. Perhaps something that can sit over the gen and cover three sides while not restricting the air for cooling.

Could be a box and you can use a fan running off the gen to cool it.

Don't overlook the simple solution.

Wooden Enclosure with Roxal Insulation for Noise abatement has been used quite successfully . You will have to route the exhaust via metallic hose and ensure two small louvered vents at either end for adequate cooling air . I have used this method for over ten yrs for both gas and diesel gen set applications of over 5000 watt applications .

***"To lower sound you can muffle it or redirect it..."***
Yes, "redirecting" can make a huge difference in the sound.

Where I work, we have a 12/24 VDC genset powered by a Briggs 12 HP single. It is mounted in the bed of a pick up and used to crank vehicles with low or dead batteries on the premises.
The muffler has a deflector louver attachment over the exhaust outlet which breaks the exhaust pulse into several "slices" (instead of one big pulse) and also turns the exhaust stream downward into the bed of the truck.
Couple years ago, the louver disintegrated from rust and that engine became so loud that all the mechanics raised Cain for management to get a new muffler "RIGHT NOW".
So a new muffler was bought and put on, but the new muffler lacked the louver.
The new muffler did not seem to lower the volume much and folks were still complaining.
When it was pointed out that the new muffler was "not exactly" like the old one, a louver was made in house and fitted to the muffler using the provided mounting holes that came with the muffler. The louver deflector did the job it was intended to do and once again it was tolerable to operate the genset.
Looking at the muffler in the photo, above I see that it too has 4 screw holes already there where a louver deflector can be added.
The trick now becomes to find a louver deflector.
I also suggest that if you can (depending on what you care to have lying in view), you might place a couple of standard, 8" concrete blocks, open cells facing upward, under the exhaust area so the exhaust is aimed into them.
The rough texture and mass, plus the open cells structure of the blocks will absorb and abate a good deal of noise.

Thanks ewalk I will give it a look.

Yes the box around the gen is an idea, just need to figure out what to use in a wet environment. The fan on the flywheel directs the air right onto the two cylinder heads at a decent rate...I could close up the sides a little and airflow will not be a concern.

I thought about having a muffler shop take a piece and bend it around near the oil filter in a 180 deg fashion and install a small auto muffler on the side of the unit, directing the exhaust towards the rear...and possibly building a baffle near the tip...I like the cinder block idea....but how to arrange the blocks with the cavity opening upward....should it not be horizontal?

Good ideas here.

***"but how to arrange the blocks with the cavity opening upward....should it not be horizontal?"***
I was picturing it in my mind with the exhaust stream redirected downward with the concrete blocks lying on the ground beneath the muffler area.
Of course if you decide to leave the exhaust on a horizontal transit, you could just stack the blocks up on their sides so the open cells face the muffler and the exhaust hits them about mid-point. Then you just stack the same number of blocks behind those with the open cells up, and the solid sides against the back end of the other blocks.
The open cells still do their thing and the extra blocks behind provide the same barrier as the ground would in my first scenario.

I played around with it and took some temps off the cylinder head, exhaust manifold, collector pipe area and will compare that to the modified exhaust to be sure I don't cook any valves.

I did pick up some reducers, pipe couplings and I was able to attach the bike exhaust and was considerably quieter. Based on my meter it went down from about 81db to 78db which is technically half the sound pressure.

Granted it's not where I want to be but it's a start.

I built a box around my generator. It was amazing how much volume of air they really need to keep cool. If you want me to dig in the manual and look up the Onan formula, let me know. I'm not sure how that would equate to what your generator needs. If it's not been said, the exhaust is 1 of several factors in what seperates a quiet one from a standard duty generator. You'll make progress modifiying the exhaust and deflecting the noise however.

Yeah, anything you can find will surely be a help. The flywheel fan apparently is responsible for the main cooling airflow across the heads and the intake supply.

I believe if I add a few panels around the motor, leaving the front open in front of the flywheel, then constructing an enclosure but adding a duct for the flywheel that should not only muffle the sound from the fan, but still allow adequate cooling.

My other concern is the exhaust heat and the generator head. I was thinking of a dual AC powered window fan and have it run off gen power.

Thinking of something like this:

Here is a link that might be useful: Window fan

When I look at my Onan RV generator book, it says to have 85 Inches squared for free air inlet. The discharge rate is 480 cubic feet per minute. This generator is a twin cylinder that brings air in one side and all the way across to discharge. I'm sure the specs are different, but it goes to show you the need to breath. It does instruct to make a baffle to separete the cool air from the warm. Using different types materials help reduce noise. Exhaust should be 3" from cabinet.

I ordered a bag of the Roxul safe n sound as recommended, should take a week to arrive. I'm going down to a local exhaust bender and see what he says..I definately need to get something to direct the exhaust outside of the enclosure.

Once we decide on the exhaust routing I will design an enclosure...and fabricating an air inlet while keping airflow in consideration.....85 sq/in sounds about right, I figure roughly a 10x12 opening lined with some extra roxul should dampen the intake growl a bit also.

I may just take the exhaust straight out of the enclosure to keep the heat to a minimum, then turn it 90 and install the muffler. I like the idea of the cinder block, figure I can run it after the muffler to the block, again lined with some roxul, and direct it upward about 24" with a cap on top the block and opening away from the house.

They enclose these permament generators with only a few grill openings and have similiar engines....I know if I do the same with fans and outside exhaust it should work fairly well.

The key to noise suppression is to absorb as much of the noise at it origin . The use of reflective or hard material often makes the issue worse. Often Styrofoam or corrugated materials have been used and noise has actually be magnified . The heat issue can be most effectively resolved with the use of one inexpensive 4 " fan located within the floor area of your enclosure , to draw cooler air into the enclosure. I usually spread about 3" of beach sand under the cabinet for drainage and sound absorption from any noise escaping from the fan area. The floor is elevated by using (4) 4" 4x4 's as legs . The Roxal insulation is not only the best form of insulation for noise abatement it also will not take on any moisture or attract any rodents. The normal enclosure is approx 4'H x 3' W x 5 L the air vents are set one high and above the exhaust muffler area one lower with a fan or without to assist with the heat dissipation at the ceiling vent. Let us know how you make out . Ensure to direct your tail pipe out of the enclosure and down towards a non hard surface , again a small portion of beach sand below the exhaust pipe will absorb additional sound . Try to keep the exhaust pipe length as short as possible the longer runs can cause back pressure . I have friends who have actually buried a small 5 gallon drum surrounded by course gravel and sand for use as a underground muffler arrangement , of course the drum must be drilled to ensure no back pressure which would cause a overheating issue with the Gen Set . All the Best Dude !