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Muffler for generator


rdickinson

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Earlier this year I asked about noise abatement for my 7kw Diesel Multiquip generator. The unit cost about 7k 9 yrs ago so it owes me nothing, however the crash in '09 crunched the enclosure and Multiquip didn't respond to my enquiries about replacement parts.....Moving on, after 22 months we fired it up out of its shroud and it ran like a top but it is a noisy sucker at 85 db's. It was initially installed under the passengers side, fwd of the fuel tank but that location proved to be a problem for any type of enclosure and leaving access for service so out it came and has been relocated.

 

With the new location and a number of sound deadening techniques the Generator noise is pretty much gone. What needs a bit of attention is the exhaust noise. The stock muffler is installed with the tailpipe aimed towards the rear of the truck b/w the frame rails.

 

The gameplan is to go with a slightly larger diameter pipe coming off the backend of the muffler, do some changes of direction and add another muffler or resonator. Something like a gun silencer or ?? We may even bring the direction forward then down. Air will change direction but noise isn't happy doing the same and is reduced every time it is deflected in a different direction.

 

Spending a pile of money on a 7.5 kw Onan was not in the cards. We've switched around a couple of circuits on the breaker panel so 6k useable is more than enough for the amount it will get used. The Inverter can be switched off while the micro and coffee pot are being use. The electric/ gas hw heater can be heated with blowpane. Fridge draw is minimal.

 

 

So the question is what muffler would be best suited for this application. It needs to be something readily available off the shelf.

 

Thanks

 

BTW does anyone know of a decent, accurate db meter app I can download?

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If memory serves me correctly, lots of lawn mowers and other small 4 cycle engines used threaded galvanized pipe for exhaust and the mufflers would just screw onto the pipe. You could do pretty much anything with the various elbows , connectors and cutting pipe to length.

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Try a place that handles commercial mowers like for golf courses, you will be surprised how big the engines are. You can get a Cummins 99HP Diesel in one of the larger rough mowers.

 

https://www.toro.com/en/golf/rough-mowers

 

If you want, I might be able to get more specific information from my son who is a test engineer with a mower company. Send me a PM.

 

Dave

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There's more to a muffler than just air flow. Baffling needs to be designed to quiet individual cylinders, thus the design for 20 c.i. cylinder would be roughly the same no matter the number of said cylinders. Of course this doesn't take into account CFM of additional cylinders and rpm..................

 

So, a trip to your friendly auto recycler might yield a muffler from a small car that could be adapted with a piece of flex pipe for acceptable results.

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There's more to a muffler than just air flow. Baffling needs to be designed to quiet individual cylinders, thus the design for 20 c.i. cylinder would be roughly the same no matter the number of said cylinders. Of course this doesn't take into account CFM of additional cylinders and rpm..................

 

So, a trip to your friendly auto recycler might yield a muffler from a small car that could be adapted with a piece of flex pipe for acceptable results.

 

In all my years of cobbling exhaust systems , I've never had good luck using flex pipe . It's good for very short term or temporary use . Much more and it will have to be replaced due to rust holes . It seems to be too thin to hold up for very long .

 

Just my experience .

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In all my years of cobbling exhaust systems , I've never had good luck using flex pipe . It's good for very short term or temporary use . Much more and it will have to be replaced due to rust holes . It seems to be too thin to hold up for very long .

 

Just my experience .

Both of our trucks, a Mack and a Volvo, have factory flex pipe, but in stainless. Yes, it will eventually fail, but it solves a lot of problems. Your motor moves, and the exhaust may too, in a different direction at times......... :o

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There's more to a muffler than just air flow. Baffling needs to be designed to quiet individual cylinders, thus the design for 20 c.i. cylinder would be roughly the same no matter the number of said cylinders. Of course this doesn't take into account CFM of additional cylinders and rpm..................

 

So, a trip to your friendly auto recycler might yield a muffler from a small car that could be adapted with a piece of flex pipe for acceptable results.

Yeah, I know its complicated, several have told me it would be a waste of time but it has worked after all. We've double layered insulation, staggered and offset intake and exhaust air, made a doghouse plus some other creative ideas.

 

The info and links have been sent to Chris and we will experiment, cast iron, welded joints, directional changes as well as mufflers.

 

The noise level is OK as it is but will be reduced even more when we complete later this week.

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Both of our trucks, a Mack and a Volvo, have factory flex pipe, but in stainless. Yes, it will eventually fail, but it solves a lot of problems. Your motor moves, and the exhaust may too, in a different direction at times......... :o

 

Factory ... I'm sure that pipe is much more , in all ways , than the pipe I could buy retail .

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Factory ... I'm sure that pipe is much more , in all ways , than the pipe I could buy retail .

I don't know if the stuff I bought over the counter was different than factory. I replaced the pipe on the Mack about 5 years ago, and it's still okay. That truck gets run a fair bit in the fall, but it's all very short trips, often less than 1 mile. Then the rest of the year it gets perhaps 4x25 mile trips a day, then will sit for 2 months. Likely worse for it than what our toters see.

 

My point was, that a short section of the flex will isolate the muffler, which will likely be solid mounted, from the engine, which on my generators, is rubber mounted.

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I don't know if the stuff I bought over the counter was different than factory. I replaced the pipe on the Mack about 5 years ago, and it's still okay. That truck gets run a fair bit in the fall, but it's all very short trips, often less than 1 mile. Then the rest of the year it gets perhaps 4x25 mile trips a day, then will sit for 2 months. Likely worse for it than what our toters see.

 

My point was, that a short section of the flex will isolate the muffler, which will likely be solid mounted, from the engine, which on my generators, is rubber mounted.

I see what you're saying .

 

I have to think that what you bought 5 years ago has to have been more robust than any I've ever bought , as I've never had any flex pipe that lasted near that long while in use .

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Roger I use a dbmeter on my android phone. I'm not sure how accurate it is, but from a relative perspective it seems to work OK. Just FYI my truck, under way on a level road is 75-76 db with the phone held near my ear. It is noticeably quieter in ecoroll coasting down a hill, but the db is about the same, interestingly. I have the D16 and it does sound different than a D13....I don't know if it is noisier though. In any case, the truck seems fairly quiet - we can certainly talk in normal voice in the truck.

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