Joe Petro

My Feedback: (1)

A friend is building a muffler for his G-23 (Midwest AT-6), and asked my thoughts.
I said you can never have too much volume. When he told me his muffler would have about a quart of volume, I really started to wonder!
Is there any such thing as too much volume?

TIA,

Joe Petro

Geistware

My Feedback: (16)

I don't know much about mufflers but engines have the muffler sized to the displacement of the engine.

Tommy Meisel

There is no such thing as too much volume unless you are using a tuned pipe. No muffler at all would be infinite volume, you are using the whole world for volume. What is significant is flow restrictions and backpressure. You could have a huge muffler with a tiny outlet and the back pressure would kill performance.

ghjr

My Feedback: (1)

Don't forget about the weight of an oversized muffler.

Chris Hinds

The more volume you have the more the muffler will weigh and the more quiet running the engine will be. If the design is such that less back pressure is provided then you will get more RPM out of the engine too.

As a guide here in Europe we figure about 10x the engine capacity for muffler capacity to make it good and quiet. If you look at some of the 7 Chamber Krumschied silencers then the capacity is even more e.g. the silencer for a 70cc engine has a capacity of nearly 900cc!!! Very Quiet! I saw two of these used on a DA150 with 32x10 prop and it was as quiet as an electric model - unlimited vertical in silence.

Chris

lynngordon

Just my 2 cents - take it or leave it. All engines are designed with a specific amount a backpressure expected from a muffler. This backpressure and the engine timing (valves or ports) are designed to put the most amount of charged mixture (fresh unburned fuel/air mix) into the cylinder.

A tuned pipe pulse forces some of the charged mixture which has flowed through the engine and out the exhaust back into the cylinder just before the exhaust port closes, resulting in a higher mass of charged mixture ready to be ignited.

With the engine tuned to a specific regular muffler, the backpressue of the muffler also results in slightly more of the charged mixture being retained in the cylinder prior to the exhaust port closure than if the engine had no muffler.

This is because the mass of the charge mixture has inertia from the downward stroke of the piston and continues to flow even after the piston starts to move back up the cylinder, resulting in some of the fresh charge going out the exhaust. The muffler backpressure, still higher than the atmospheric pressure at this point, will keep more of the fresh charged mixture in the cylinder instead of just letting it flow through as in an open exhaust or extremely free flowing muffler system

Again, just my 2 cents.

Geistware

My Feedback: (16)

lynngordon,
I guess in my lame way of putting it, the muffler is sized for the engine. I don't know the details but I do know that some engines don't run as good with zero backpressure.

kevin mcgrath

My Feedback: (1)

Chris.....Im assuming your remarks pertain primarily to semiscale aerobatic planes,but what about scale? For example what would be a typical old country muffler design approach to a 60cc gasoline engine in a radial cowl bipe like a Stearman or Jungman?
When you refer to a muffler setup that is "very quiet" do you have any idea what the DB ratings are and the parameters under which they are measured? The World scale championships are here in Ontario Canada in about 10 weeks. Im attending and Im very curious to see what the noise levels will be...
Thanks.........

Diablo-RCU

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For an un-tuned muffler system, more volume is always better for power because it allows better scavenging of spent exhaust gases and also allows a higher differential pressure between the transfer ports and combustion chamber - thus better cylinder filling. I know of no examples where an un-tuned muffler developed more power than an open exhaust with no muffler. The fuel mixture probably will have to be adjusted for the different gas flow through the engine. Fuel consumption will most likely increase as exhaust back pressure is decreased. Engine temperature will decrease as back pressure decreases. I doubt that the gas engines are developed with a specific muffler in mind. If that were true, then the engine manufacturers would provide the engine with THEIR muffler......instead there are a half dozen muffler manufacturers providing slightly different products for the same engine.

Chris Hinds

Kevin,

I don't have any ideas of dB levels of the models themselves, but I would say well under the UK 82db/7m (22') rule. Even for scale models the tendancy in the UK is to muffle the engine as much as poss. They often sound realistic but quiet. As a friend of mine (flying F3a pattern) says "there is no reason why exceptional levels of power can't be combined with exceptional silence"

regards


Chris

kevin mcgrath

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Kinda expected your reply and I agree with the doesnt have to be noisy statement.We are installing an industrial noise meter setup at our fun fly this weekend as an experiment,and I expect to see levels pushing 100.....