Hey I have a question though I am not new to RC Engines at all. I am just curious to what happens to a Nitro engine say the Super Tiger .40 Ringed when you dont use a Muffler at all. I have never run a Nitro Engine with out a Muffler before so I have no idea, But I do have a few assumptions. 1 Noise 2 Loss of pressure in the fuel tank. Though a Fuel pump can take care of that and I could Bear the noise or at least Dampen it some how. Again Does the piston burn up or Does nothing at all happen? Thanks Anthony.

1. It is too noisy.
2. There is no pressure to the tank which leads to inconsistant fuel flow.
3. Without the backpressure from the muffler you will not get a good idle as the plug will want to cool down. Before mufflers they used to put rotating baffles or covers that moved in or over the exhaust port. My first K&B 40 had such a baffle linked to the throttle.

The real reason an engine with an open exhaust won't idle very well is because fresh air gets sucked back into the exhaust port and leans the fuel air mixture. With a muffler, only air that has the oxygen burned out of it reenters the cylinder and the air fuel mixture gets diluted with exhaust but does not go lean.

Spark ignition engines won't idle either without at least some sort of header pipe on the exhaust port so there goes the "you need backpressure to keep the glow plug hot" theory. Engines that only run at full throttle (control line engines) do just fine with an open exhaust. Rotary radial engines used in a lot of full scale WWI aircraft also would not throttle down for the same reason so most of them used a kill switch to run the engine in bursts when waiting to take off or during landing.

It's likely the plug might cool down too much at idle which would mean raising the idle speed to keep it lit or fitting a 4 stroke plug might help. Almost all engines have far too large a carb for good fuel draw which is why muffler pressure is needed for anything other than level flight (or a test stand). If you wanted to fly with no muffler and the engine wants to die off lean with the nose up check then a work-around fix is to set the carb barrel to only fo maybe 3/4 open and retune the mix for that opening. This simulates having a smaller carb with better fuel draw.

Running with no muffler has no affect on the piston because this was the way all engines used to run before noise became an issue.

I cannot give you any technical data on running no muffler. I can tell you when I first started with model glow engines there was no such thing as a muffler. At least not one I had ever heard of. Then a few years later people started talking about the day all of us would have to run with a muffler. You should have heard the screaming and shouting. "We will be so underpowered with mufflers our planes will never fly", and the likes.

Bob

OK I kinda figured it would have Negative reactions with no muffler, Why else would there be one if not for a mechanical reason besides Noise comfort. Thanks.

I've ran a lot of spark ignition engines without a muffler--both four stroke and two stroke. Loud, yes, but they run--and run like a stuck pig at that.

I can tell you what happened to me when my muffler came loose in flight. The engine started running really rough and lost a lot of power, eventually it dead sticked before I could get it back in for landing. After it landed I found the nut on the end of the muffler (a Tower Hobbies .46) had come off. Put a new one on and it was as good as new.

Because You lost muffler pressure and the engine leaned out and stopped.

Cheers

I rebuilt a 6 cylinder Chevrolet car engine and decided to start it up before I had the exhaust manifold bolted on. It was loud, it ran, but I had to keep giving it gas to make it run. If I tried to let the engine idle, it would quit. I figured I would adjust the idle after putting on the exhaust but after the exhaust system was installed, it idled perfectly with no adjustments to the carb.
I noticed a similar phenomenum when I took the pipe off of a two-stroke motorcycle I owned and let the exhaust come straight out of the port. It didn't need the muffler to idle normally, it just needed the header pipe.
The most logical explanation for this is that when the throttle is closed, engines blow out some exhaust and then suck a little back in before the exhaust valve/port closes. Without a short exhaust pipe, the engine sucks fresh air into the cylinder resulting in a leaned out idle mixture. It may be possible to adjust the idle mixture to compensate for this.

You can run without the muffler, but it has to be MUCH richer, you are blowing out alot of fuel without the muffler attached, and keep it between 1/2 and full throttle and it will run waaay faster, more intake because of less restricted exhaust equals more POWER...not great fuel economy if that concerns you...alot of fields wont let you fly without a muffler other than .049...Rog

I really enjoyed flying RC in days before mufflers were used and like many I went through all the pain and anguish clubs experienced mandating mufflers in the late 60s. At the time the Descent almost destroyed our club. The un-muffled engines had baffles that closed over the exhaust port as the throttle was retarded and they ran very strong and idled like a dream. Many of us few at public fields and gave up flying at the club fields until the muffler technology improved. You get more power without a muffler and less engine heat buildup. The real solution to mufflers is to use a tuned pipe so you get more power and low noise.

As downunder told everyone, without the muffler pressure the Carbs on modern engines are far too overbored to draw fuel. That venturi has to significantly increase dynamic pressure so there is less static pressure for fuel to flow. Bore it out and you get no fuel flow, simply because the increased area doesn't require adequate airflow velocity to significantly increase dynamic pressure with the resulting decrease in static pressure, that really sucks the fuel. I make carb restrictors for sport engines for club friends so they get more steady and reliable engine runs.
Pull the muffler pressure line and go up without changing the needle valve. See what happens.

Back in the unmuffled days, the carb throats were much smaller than today for a given engine size. They ran more reliably, yet not nearly as strong.

Go fly your Dubb Jet with a carb hole that can swallow a bird. You have to really under prop it so as to obtain the RPM required to feed that monstrous hole. Otherwise expect flameout right after T.O.

Of course there are true pressure tanks, but then the idle really suffers. If you want the best of all worlds, Try one of Dubb Jett's BLADDER tanks. Very neat, but alas, you gotta' have muffler pressure! [sm=52_52.gif]

If you just have to have the ultimate power, then simply increase cubic inches.