Onan 4000

[Discn]

Looking for a quieter exhaust system for Onan 4000 generator

[16ACE27]

The exhaust noise is just a fraction of the total noise created by the generator. Some have added a small resonator to the tail pipe. There are several YouTube videos of people testing different methods to quiet the 4K exhaust.

[Rvman12]

Resonator on Amazon...mixed reviews.

[Pete'sMH]

Perhaps Onan will come out with a new generation of quieter models. My new class B has a newly designed 2800i. It is fuel injected, starts instantly and is as quiet as the air conditioner. Much, much better than the previous 2800. The 4000 models have been pretty much unchanged since the Nixon administration. It’s time….

[DavidEM]

Originally Posted by Pete'sMH

Perhaps Onan will come out with a new generation of quieter models. My new class B has a newly designed 2800i. It is fuel injected, starts instantly and is as quiet as the air conditioner. Much, much better than the previous 2800. The 4000 models have been pretty much unchanged since the Nixon administration. It’s time….

I just had a conversation with the GM of the Albany, NY Cummins sales and service center along those lines.

Cummins seems to have dropped the ball in upgrading their RV generators to the new inverter design. The upgraded QG 4000 generator was supposed to follow right on the heels of the first QG 2800i inverter generator released about two years ago. It didn’t happen and as far as the Albany GM knows, there are no plans to do so.

Sad that we have to live with the noise as well as ethanol in the gas fouling the carburetor on QG 4000 and 5000 models (the new QG 2800i has EFI, ie no carb).

David

[Beau388]

Originally Posted by Discn

Looking for a quieter exhaust system for Onan 4000 generator

My coach came with a Onan 4000, but the exhaust runs around the propane tank and exist under the hydraulic system for the jacks. The total length is about 6 feet with two 90 degree bends. The exhaust is quiet enough that I cannot hear it over the engine's mechanical noise. The cell phone apt shows the sound level at 62 db 10 ft from the generator when on grass and 64 db on pavement running a 15,000 btu roof A/C. The OG4000 runs 3,600 rpm but the QG5500 is a twin at 2,400 rpm and you can get it with fuel injection.

[The Gritz Carlton]

Air cooled engines are not as quiet as water cooled ones. Exhaust modifications may help but I would run your idea by Cummins/Onan techs to make sure you're not creating too much free-flow or back pressure. You won't get as much noise relief as you may think. Maybe try more insulation around the cavity the generator is mounted in...if space allows.

[DavidEM]

Adding an exhaust resonator or similar will help some, but not as much as you may hope.

In an air-cooled engine there is no water jacket to help dampen combustion noise pulses. In fact I suspect as much noise comes out of the air cooling system as the exhaust. And there is no way to dampen that source of noise. If you do you will probably restrict airflow and overheat.

The best way to reduce noise is to run at a lower rpm as in an inverter generator. Also lower rpm and EFI is more efficient which means less fuel burned which means less noise.

That is why I truly hope that Cummins will release an inverter version of the
QG4000 like the QG2800i.

David

[Pete'sMH]

Originally Posted by DavidEM

I just had a conversation with the GM of the Albany, NY Cummins sales and service center along those lines.

Cummins seems to have dropped the ball in upgrading their RV generators to the new inverter design. The upgraded QG 4000 generator was supposed to follow right on the heels of the first QG 2800i inverter generator released about two years ago. It didn’t happen and as far as the Albany GM knows, there are no plans to do so.

Sad that we have to live with the noise as well as ethanol in the gas fouling the carburetor on QG 4000 and 5000 models (the new QG 2800i has EFI, ie no carb).

David

That’s too bad. But I guess Onan pretty much owns the RV generator market and they feel like they don’t need to update their products. Seems like there’s an opportunity for someone else to enter the market with a better product. Honda, maybe.

It may seem like a minor point but the 2800i was a pretty major selling point for me when we downsized to a class B.

[Beau388]

Originally Posted by Pete'sMH

Perhaps Onan will come out with a new generation of quieter models. My new class B has a newly designed 2800i. It is fuel injected, starts instantly and is as quiet as the air conditioner. Much, much better than the previous 2800. The 4000 models have been pretty much unchanged since the Nixon administration. It’s time….

RVMP makes RV inverter gensets in 4000 and 5500 watt sizes. The RVMP 4000 is rated at 48 db where as the Onam QG4000 is rated at 68 db. <https://rvmp.co/products/flex-power-4000i-rv-generator>

[DavidEM]

Originally Posted by Beau388

RVMP makes RV inverter gensets in 4000 and 5500 watt sizes. The RVMP 4000 is rated at 48 db where as the Onam QG4000 is rated at 68 db. <https://rvmp.co/products/flex-power-4000i-rv-generator>

That is a very interesting generator, particularly using the alternator fed with 3 phase power to start the engine which eliminates a DC starter. The noise levels and fuel consumption are quite low as well.

They say that Forest River and Thor install them on new coaches. Anyone have any experience with that?

David

[MJC62]

Our 2006 Gulfstream had a Generac 4000 W genset. IMO it was a better unit than the Onan if for no other than it had an oil filter.
Unfortunately, I don't think Generac makes RV gennys anymore as their focus is now on home standby generators

[Redsand]

We have the Onan 4000 as well and with no mods whatsoever is quieter than my home 4kw setup. Our home setup for reference is enclosed in a semi soundproof enclosure and the Onan is just a small purr by comparison. Exhaust as stated is a very small noise maker on both units.

[Chateau_Nomad]

As ACE said in the second post, the exhaust noise is just one source of noise. Depending on the installation, the generator acts like a sound system speaker. What you are hearing is the sum of every vibration caused by the running generator.

And that's why the exhaust resonator helps on some rigs, but others may not be much improvement at all.

The ONLY way to significantly reduce the noise is to isolate and absorb ALL vibrations - even the plastic and metal generator case parts. But then you introduce problems with heat dissipation, which could damage the generator.

The best solution is for Cummins to redesign the whole machine.

[DavidEM]

Originally Posted by Chateau_Nomad

The best solution is for Cummins to redesign the whole machine.

If they would just start selling the 4 kW and 5.5 kW inverter generators, most of these problems would be solved.

David

[16ACE27]

Originally Posted by DavidEM

If they would just start selling the 4 kW and 5.5 kW inverter generators, most of these problems would be solved.

David

Inverter generators are great at partial loads. Less RPMs equals quieter exhaust and less rotational noise. In addition, the suitcase inverter generators incorporate noise attenuation cases that help keep them quieter.

But, the difference in noise at full load between a 4 KW inverter generator and a 4 KW "analog" generator is minimal. In fact, a poorly made inverter generator may even be louder as it has to make up for efficiency losses in the inverter section.

[Beau388]

Originally Posted by 16ACE27

Inverter generators are great at partial loads. Less RPMs equals quieter exhaust and less rotational noise. In addition, the suitcase inverter generators incorporate noise attenuation cases that help keep them quieter.

But, the difference in noise at full load between a 4 KW inverter generator and a 4 KW "analog" generator is minimal. In fact, a poorly made inverter generator may even be louder as it has to make up for efficiency losses in the inverter section.

Tier 4F emission specs for small gasoline engines are hard to meet at best with constant RPM air cooled engines. That is the main reason for fuel injection in the QG5500. Even the RVMP 5500 inverter generator idles at 2,400 rpm just so it can meet Tier 4F specs.
My engineering back ground says: it got to be water cooled or run on propane to make a 5500 watt inverter generator idle at 800 rpm and still supply 5,500 watts at 2,400 rpm. The reason there are no more air cooled passenger cars is, they couldn't find a way to make them meet Tier 2F emission requirements.

[Pete'sMH]

Our new class B has the new(ish) Onan 2800i. To be sure it is smaller than the 4000 models but it is a significant improvement over the previous 2800 models. The old ones are every bit as loud as the 4000 while the new one is as quiet as the A/C. I was told that Onan was planning to issue a new fuel injected, inverter based 4000 model this year but that it was delayed or cancelled after Covid. Who knows? It would be a huge improvement for the entire industry.

[1Hurricane]

Originally Posted by Beau388

My coach came with a Onan 4000, but the exhaust runs around the propane tank and exist under the hydraulic system for the jacks. The total length is about 6 feet with two 90 degree bends. The exhaust is quiet enough that I cannot hear it over the engine's mechanical noise. The cell phone apt shows the sound level at 62 db 10 ft from the generator when on grass and 64 db on pavement running a 15,000 btu roof A/C. The OG4000 runs 3,600 rpm but the QG5500 is a twin at 2,400 rpm and you can get it with fuel injection.

sounds like you need to better insulate the generator compartment..

[Chateau_Nomad]

Originally Posted by 1Hurricane

sounds like you need to better insulate the generator compartment..

Then you introduce air flow / cooling issues... which could even void the warranty.

Before the motorhome, I had two Champion 2000k inverter generators with a parallel kit. Running both at full throttle they were quieter than the Onan with essentially the same output. The "throttle-down" feature made the MUCH quieter. Caveat... the Onan is a much more robust unit with much better hours/life capability.