Got a few question for the muffler guru’s out there.

I am posting this in two forums to ge tas much feed back as I can.

It is about inlet and outlet size.

Should the outlet tube be same size or larger than the inlet opening in sq mm or would it help to be smaller.

I know that the tuned pipes I have a 25mm inlet and a 16 mm outlet tube and makes the engine gain a few more rpm’s and does not cause the engine to over heat.

I believe canisters are about the same with inlet and outlet tubes.

I guess my point is if the outlet has a smaller outlet tube or the same size as the inlet will it cause the engine to over heat and void any engine manufactures warranty. ?????


Milton

Interesting question.

Karol

I'm not an expert in muffler design. If I was, I would answer you, but then I'd have to bill you. (smile)

I guess the most efficient kind of muffler is the kind with no exhaust opening, when it comes to creating maximum quietness. But we have to open up the muffler a bit or the engine will stop running. However, if we open up a piece of pipe without first giving the hot engine gas a chance to expand (cool off/reduce pressure), then we really haven't muffled much of anything. So, we need to use what is known as an expansion chamber. No, not the tuned pipe type, necessarily, but some place where the gas can expand and reduce its pressure without creating external sound waves. Oh, but were it that simple, I'm sure you are thinking.

You ought to hear some of the engineering types that frequent this forum when they start talking about this subject. They begin dropping fancy names in physics such as Bernoulli, Munchaussen Syndrome (?) and a few others that I'm not familiar with. I think I'll leave all the fancy talk up to them. Chow!


Ed Cregger

That's a fairly nice start to get things rolling Ed [sm=thumbs_up.gif]

Karol

Subscibed. I want to buy a DLE-20 but am worried about the noise so I am really interested to see where this thread goes.
John

A two stroke needs to have back pressure to stop the outflow of gas from the cylinder the very moment the transfer ports close. If the outflow is not stopped in time, fresh mixture escapes and there is less to burn. You loose power that way.
Without getting into complicated stuff, the stinger (outlet) can have about the same size as the carb. The exhaust port is much bigger than that, but that is only needed to get all that gas pressure down before the transfer ports start to open. The much needed back pressure can be adjusted with the stinger diameter and first expansion volume of the muffler system. There seems to be an inverse ratio between chamber volume and stinger diameter. Small volume chambers only perform very well if the stinger diameter is large. Large volume systems can have much smaller stingers, and thus can achieve better noise attenuation without power loss.

How far do you want to get in to this here? It's really quite a science. Would it help to offer that a wrap around Pitts is quieter than a stock muffler, a wrap around Pitts with an oversize can section will be quieter yet, a header/can arrangement might be even quieter, and if you'd like to spend the money, you can make it quiet and pick up some power with a header/tuned pipe arrangement?

The why's and how's on the tuned pipe arrangement would fill a book. Should really be approached, I think, by guys really into that kind of thing, with the time and patience to sit down and figure it out, then spend some time (maybe a lot of time) experimenting with the engine they're interested in messing with. There's a lot to it, and much to be gained.

Yes back pressure does make a lot of to do how a engine runs.It effects how they Idle, how fast they warm up and the top rpm is also effected. The photos below show a power exhaust valve, a bolt that is adjustable (varies back-pressure) and a photo of a exhaust valve I made for my DLE 30. It was linked to the throttle & would open & close at the same time. It seemed to work well for me. I could not get a manufacturer to bite on it? I still may make another version that will fit on the outlet of the semi -tuned exhaust. Capt,n

Nice work John.
In racers the saying is, the system is large enough when you burn your legs on it!
With modern monoshock bikes the packaging got better, and burnt legs are a thing of the past.
However, it seems that history repeats itself. Now Model plane pilots are whining that they get hurt by a proper exhaust system.

again, as many of the above posters i am no expert....

however this is what i have gained from my pylon racing experience.

Stinger diameter worksbest when smaller than inlet size ( the whole back pressure story), but only if there is first sufficient volume as in a tuned pipe system. As well as tuning the length of the header and pipe combo, you can also 'tune' both the stinger length and diameter. There are so many theories the best way is just to experiment and see the results first hand, as that is what works for you with xxx motor and xxx setup etc. the variables are so great it may be different for the next guy. dont forget change the prop, heat range of plug etc etc and all the setup starts again.

if you are running cannisters or a tuned pipe make sure the header pipe is of equal cross section to the exhaust outlet.

try adding a length of say 70- 100mmlarge diameter silicone tubingto the stinger on your std mufflers, I have done so and found a reduction in noise, but also a marked drop in rpm in some cases. I never checked head temps because it never resulted in any gains so i just removed it and never flew like that.

I think if you are referring to reducing the outlet of std side dump mufflers with small volumes to increase pressure it could be erring on disaster. I havent tried it so maybe not, but i would watch temperatures very closely.

100% agreed.

I guess to simplify my question a little more.

Would a muffler with the same outlet size in sq mm the same size as the inlet cause a engine to over heat and damage the engine. ????

I think I know the answer but would like to get some input from others about it.

I understand how a tunes pipe or canister work’s, could never actually make one, but do understand how the right amount and at the right time back pressure can hold more fuel in the cylinder for better performance.

Milton

I think if we really want the answer to the original question we'll have to ask a female engine.

Did you mean to say "female engineer"? I understand they like long stroke pumper engines, but I don't know what they like to wrap around their neck in the winter. I have not known one to overheat due to a small stinger though.

Regards, Richard

Well, talking of stingers... Gees, It's past midnight again!

Nope, I meant engine. Is the size of the muffler important to a female engine. For sake of arguement, we'll presume the male engine has the muffler.

Milton,

We have to consider that the exhausted gasses get cooled by contact with the relatively big area of the sheet metal skin of the muffler.
Then, the volume of the gasses is reduced between inlet and outlet.

As you know, the main purpose of the mufflers is to quiet the noise by interference of the sound waves, and get the back pressure from friction of the gas and changes in speed and direction.
Normally, the resonance and overcharge that happens in the pipes don't happen inside mufflers.

The manufacturers try different shapes, chambers and diameters, until they get a compromise among noise reduction, backpressure, available room and production costs.

Check this out!!! http://www.youtube.com/watch?v=tHTPciAi4XU&NR=1 Capt,n

Different engines require different exhaust criteria. Some tighter and some not as tight.

Milton,

provided the flow of gas is unrestricted, i would say, no.

Captn
nice video, as said earlier i found the same thing, worked quite well as a sound dampener, but i also had quite a loss in rpm, up to 600rpm drop if i remeber right....

I am just trying to find out if I have the wrong thinking about something that happened a couple day’s ago.

Had a customer to call me and tell me something that just blindsided me.

I sell quiet a few mufflers for different popular engines, Had sold him a set for a 100cc class engine and he wanted a refund on them.

Seems that the manufacture of this particular engine had told him that there outlet tube was larger than mine and if he used the mufflers it could possibly cause the engine to over heat and possibly void his warranty, Now they did say possibly, which is enough to put doubt in any ones mind.

I have had nothing but respect for this company for years and lost it all in one phone conversation.

The mufflers I have for this engine have a 25mm round inlet and a 25mm exit tube.

To me this is hog wash and just a scare tactic to sell products but I could be 100% wrong on this. ????

I guess the China made products are really hurting there sales for them to use these type of statements to sell there products.

But it is there engine, There story so they can tell it anyway they want to.

Milton

I don't buy that manufacturer's argument; for me, same diameter in and out is more than sufficient.

As I explained above, the exhausted gasses get cooled inside the muffler and the volume decreases; hence, the speed (and friction loss) in the outlet will be smaller than in the intake of your particular muffler (unless it is a dual muffler with two inlets and one outlet).
Besides, the guts of the muffler make a difference in counterpressure and proper evacuation of gases that that manufacturer does not mention.

No much to do about an over-concerned costumer.

In general, two stroke engines with excessive exhaust restriction loos power and work hotter.

Lnewqban - "Vision without action is a daydream. Action without vision is a nightmare." - Japanese proverb

No wonder it seems like ever thing is a nightmare....my vision is not so good...but getting a little better!

I would say that exhaust with a 25mm inlet & outlet should work fine. When gasses cool they take up less space...hence some exhaust systemshave a lot smaller outlet. The guy should give it a try anyway....unless he lives in a hot dessert area. Capt,n

He will not be using them, I told him I had no problem giving him a refund so they are there way back to me.

If a manufacture told you if you did not use there product with there product or you could possibly void your warranty, What would you do. ???

Milton

I would have to think about that one....before I (that ismeme) strarted cussing.