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Running a Generator With No Muffler


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  #11  
Old 01-07-2018, 09:49:58 AM
KPack KPack is offline
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Default Re: Running a Generator With No Muffler

Wow I donít know what to say.
https://m.youtube.com/watch?v=OpXwzbZ95hY
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  #12  
Old 01-07-2018, 12:47:05 PM
Jim Marcozzi Jim Marcozzi is offline
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Default Re: Running a Generator With No Muffler

The whole "burn a valve" thing because of back pressure or reversion is a myth.

The REAL reason that a valve can burn is that if your fuel mixture is set WITH a muffler in place and now you remove it, you will create more air flow through the engine at higher given throttle opening at load because of a lower back pressure, which makes your (once good) mixture now lean. Lean = heat. Prolonged lean running can and will damage a valve. It has nothing to do with cold air sucking in or any of the other BS that float around the internet or is spewed by hot rodders from 50 years ago.

The whole "an engine needs back pressure" thing is not true. When you hear someone complain that they changed the exhaust on their car and now it runs worse, someone always makes the claim that it needs back pressure to properly run. What it really needs is the mixture under load corrected for the additional air flow.

Ideally, I'd set the mixture on a genset at 100% load by using a pyro in the exhaust ports and going by EGT and also 4 gas analysis, but this isn't realistic, nor is it my car that I run 28 PSI boost on with good fuel. If you open the genset's exhaust or even change mufflers, I'd always recommend readjusting the main carb jet or gaseous flow as per manufacturer. Anyone who races a 2-stroke dirt bike can tell you the importance of readjusting the fuel for even the slightest exhaust change or even cleaning the muck out of the muffler or expansion chamber and making more high load airflow.

TUNED equal length and volume headers, 2-stroke expansion chambers, H-pipes and other exhaust trickery can actually make negative exhaust pressure on an exhaust port and aid in drafting more air into an engine. Not only do these engine see no back pressure, but they have exhausts under a slight vacuum with operating at a specific RPM range. That's also known as the "powerband" in the 2-stroke dirt bike world.

I've dealt with this over and over in the earlier days of EFI injection on 5.0 Mustangs, IROCs and TPI Vettes. Everyone was convinced that these cars needed BP to run properly since most gear heads at the time knew zero about EFI and how to tune it. I was one of the few that actually knew how to recal the MAF and even eventually was able to change data and re-flash new PROMs to correct the fuel on the GMs.

Any internal compression combustion engine is always more efficient with no (or negative) back pressure, but fuel and timing have to be adjusted properly, as with any engine.

So go ahead and straight pipe it, but make sure it's adjusted properly. I'd also invest in some Kevlar through if you have close neighbors !
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Old 01-07-2018, 01:23:37 PM
AngrySailor AngrySailor is offline
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Default Re: Running a Generator With No Muffler

Of course the mixture must be maintained but have you ever tried placing a wide band O2 sensor within about a foot of the end of a header collector and tried to get a stable reading? Reversion is most definitely happening and will be dependant on the cam profile and induction to a degree.
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Old 01-07-2018, 01:37:10 PM
Jim Marcozzi Jim Marcozzi is offline
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Default Re: Running a Generator With No Muffler

Reversion IS happening but it has nothing to do with burning or damaging a valve. It's relevant to cylinder scavenging and the size/area of the peak power band.
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Old 01-07-2018, 02:26:28 PM
nothingbutdarts nothingbutdarts is offline
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Default Re: Running a Generator With No Muffler

I know this is an Onan generator sight BUT, The knowledge on this Onan sight it overwhelming in reguards to "performance" minded people.
I klnow there is a general discussion heading here on the STAK , however it would be KOOL if there could be a "Engine/Car/Motorcycle "Performance" discussion area!
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Old 01-07-2018, 03:15:09 PM
len k len k is offline
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Default Re: Running a Generator With No Muffler

Headers on race cars are tuned to make a vacuum at exhaust valve to increase air flow. So I don't think back pressure is needed.

On a 2 engine 10 passenger commuter airplane flight I took once at dusk. I saw engine had ~ 3-4 feet of exhaust pipe with no muffler, glowed dull red entire flight. Seems no muffler was obviously for power and weight reasons, looked factory. Besides FAA would have a fit if owner modified it.

Odd that carb can't maintain steady air/fuel mixture if change backpressure (remove muffler) Maybe it's just a quirk of carbs. But would think as increase airflow more fuel would be drawn thru main jet

Last edited by len k; 01-07-2018 at 11:26:42 PM.
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Old 01-07-2018, 05:28:57 PM
Newoldstock Newoldstock is offline
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Default Re: Running a Generator With No Muffler

All exhaust systems add some back pressure.
When you reduce this you increases the amount the engine can suck on the carb and you will lean out the carb.
This is physics and not in dispute, what is likely to colour your view of this is is how rich or lean you carb was from the start.

Cold shock can bend valves if the exhaust port is open.
Even if it is not there is a possibility of an overheated engine behind a valve if you run a cold exhaust ( thin header pipe and no warp ).
This almost never happens in practice because the engines we are talking about here have small valves, small ports, small exhaust and usually a lot of iron to hold some of that heat for a uniform cool down.

I have had some troubles with some very expensive stainless valves in some very large free breathing engines with short open exhaust.
Solution is make sure both valves are sitting on a seat for cool down.

Open headers.
My neighbors do not like loud engine noises so I try not to run any engines around here when they are outside and can clearly identify me.
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Old 01-07-2018, 06:23:48 PM
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lokay5 lokay5 is offline
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Default Re: Running a Generator With No Muffler

Quote:
Originally Posted by brae View Post
the engines efficiency may change some however, i doubt it will damage anything but your ears.
........whaaaat? ? ?......
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Old 01-07-2018, 07:11:28 PM
Newoldstock Newoldstock is offline
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Default Re: Running a Generator With No Muffler

It is a pumping loss.
So it will impact efficiency.
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Old 01-07-2018, 11:35:44 PM
JoeE. JoeE. is offline
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Default Re: Running a Generator With No Muffler

Along these same lines, I ran a locomotive yesterday... I think it was a 12 cylinder... diesel...

At idle, all sounded normal. As I put a load on it... get the RPM up to about 700, a whooshing sound like the exhaust of a steam locomotive came out from under the hood... and got louder and louder... if I let off the throttle it would lessen, but would come back on when I came back out on it...

Finally, set the brakes tight and put the throttle in 2 and ran out and opened the doors on the body...

I was surprised to see that one of the exhaust manifolds had broke loose from the exhaust port on the number one cylinder... and while the broken part was still attached to the "muffler", the exhaust gasses were forcing it away from the head.. and the noise was deafening in there... soot covering everything...

Heck, it rolled in here, it can roll out.. we'll let someone else worry about it!
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