# Muffler for model i.c. engine



## Brian Rupnow (Aug 23, 2018)

Just for the heck of it---has anyone ever built a muffler for a model i.c. engine? I have designed one this morning, based mainly on guess-work and size constraints. This muffler is designed to fit onto my flathead single cylinder engine which I designed and built a few years ago. This engine currently has a "straight pipe" on it, although the straight pipe has some fancy carving on the outside of it. Since I don't have a decibel meter, I will have to post a video showing the engine running in its current configuration, and a second video with the muffler installed on it.


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## Brian Rupnow (Aug 23, 2018)

This picture shows the flathead engine in its current configuration.--The exhaust is really just a straight pipe, in spite of the fancy carving on the outside of it.


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## bjo (Aug 23, 2018)

If you have a smart phone, there are free decibel meter apps.  I doubt they are very accurate but could give a ballpark.


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## Brian Rupnow (Aug 23, 2018)

I don't have a cell phone. This video shows my small flathead engine running, so you can hear the current noise level. Really, it isn't that loud even with a straight pipe on it.


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## XD351 (Aug 23, 2018)

Maybe you could copy something like a briggs muffler ?
They are not much more than a straight thru pipe with a plug half  way down the pipe and radial holes drilled either side of that plug to let the gas flow through the chamber and then into the holes drilled on the other side of the plug . 
You of course would have to tart it up to match the engine ! 





BTW the motor runs real nice !


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## goldstar31 (Aug 23, 2018)

It's a long time ago since I played with model diesels or compression ignition  engines but my old Mills and Ed's and whatever were unsilenced but following this it seems obligatory in the UK to fit a silencer/muffler.
All that seemed to suffice was a bit of tubing to cover the exhaust ports and obviously be opened up at that point.
They were merely clamped with a single bolt.

If this is old hat, please delete

Norm


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## Brian Rupnow (Aug 23, 2018)

One thing I have to be careful of.-I mix a bit of 2 cycle oil with my gasoline, for the sake of my Viton o-ring on the piston. None of my small engines run hot enough to burn this oil, so there is a steady fog of oil mist coming out the exhaust. I have to arrange things so there is not an oil trap built into the muffler.


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## Cymro77 (Aug 23, 2018)

There you go again Brian!  A rather short vacation!!  I love it when you take a vacation.


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## Charles Lamont (Aug 23, 2018)

Size matters. To be effective in evening out the pulses it must need to hold more than one cylinder-full of exhaust, but how many?


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## XD351 (Aug 24, 2018)

Brian , couldn't you use the muffler as an oil trap and add a small drain plug or tap on the bottom ? It might stop it spitting oil all over the place like a two stroke nitro engine !


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## Brian Rupnow (Aug 24, 2018)

Went to bed last night and thought--and thought--With a bit of redesign I can make the two purple colored pipes identical. This also introduces another set of baffles ahead of the outlet, and gets holes down close to the bottom where any trapped oil can flow into the exhaust tube to be expelled.


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## peter2uat (Aug 24, 2018)

Have a look at the ASP .91 at
https://www.nitroplanes.com/fm01-20-fs91ar-asp-nitroengine.html 

a better dampening muffler for 2-stroke engines I found in a magazine from 1996 (see attached retranslated and modified file).
A four stroke engine will need a muffler volume of approximately 1 x engine displacement.
I just had a look at the air refresher in our bathroom…
Hmm -  2.5 x 0.8" = 1.5 cubic, should do nicely


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## Mark Duquette (Aug 24, 2018)

What we used for our race cars was very simple just tubing and bent disc to create a spin in the exhaust.


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## Brian Rupnow (Aug 24, 2018)

So--Here we are with the center parts all soldered together and the outer shell slid into place. The center consists of the two 5/16" o.d. tubes that extend out from each end plus the center plate with a bunch of holes drilled in it. I'm not going to show you the insides, because it is soooooooooo ugly. How ugly is it?--It's ugly enough that if it were a part that showed I would make it over again. However, that nice clean outer shell hides a lot of sin. Tomorrow I have the two endplates to make plus the flange which bolts to the engine.


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## Brian Rupnow (Aug 25, 2018)

The new muffler is finished and installed on the engine. If you look on top of my ignition box you will see the old straight pipe setting in the lower left hand side of the picture. The new muffler turned out looking great. There was some really nasty blobby silver soldering inside, and of course the flat divider plate between the two tubes twisted and bent all to hell from the heat. Some quality time with a small body hammer and various pincer type tools got it sorted out to the point where it was good for functional but too nasty to show people. Next step will be to make a video to compare how loud the engine is now compared to what it sounded like with the straight pipe on it.


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## Brian Rupnow (Aug 25, 2018)

And here we have a video of the engine running with a muffler on it. I think it is quieter than the video I posted earlier in this thread when it was running a simple straight pipe exhaust. Let me know what you think.---Brian


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## Brian Rupnow (Aug 25, 2018)

Lets face it--we are generally happy just to see our engines run, and be able to rev up or idle down on demand. There IS a lot of mechanical noise from these small engines. I have removed the muffler and am doing some remedial work on the flange which attaches it to the engine. Although I did use a jig when I soldered the flange on, it was a crummy jig and the flange turned out quite crooked in respect to the muffler body. I was able to fully tighten the two top shcs, but not the bottom ones. I will show the new jig I am making to correct this issue, and then will repeat the sound test.---Brian


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## Brian Rupnow (Aug 25, 2018)

I have removed the flange from the muffler, made a new flange, and made a welding fixture to align the new flange properly with the muffler body. The four dark blue shcs are "sacrificial"--That is to say, they will end up silver soldered to the face of the flange--not on purpose, but unavoidable when soldering in such close proximity. The heads will be machined off after the flange is silver soldered to the muffler. Then the two pink/purple shcs will be removed and the green angle (with muffler and flange still attached) will be   pulled straight out of the blue fixture block. Then the dark blue shcs will be drilled out if necessary.


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## Brian Rupnow (Aug 26, 2018)

I reworked the muffler flange, and re-soldered it using the welding fixture shown in the previous post. I got lucky with the four dark blue socket head cap screws--Three of them unscrewed and I only had to drill one out. The muffler is reinstalled, and it seals properly to the engine now. The noise level has dropped a bit more, but trust me---Ya wouldn't want to have to sleep in a room with this engine running beside your bed.---Brian


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## minh-thanh (Aug 26, 2018)

Nice !
Thanks for share ! I will do it 
And  if possible, please add some pictures of your engine. I like it


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## ShopShoe (Aug 27, 2018)

Brian,

It's a different experience to hear the mechanical sounds of the engine without so much of the exhaust noise, but I don't have an opinion as to which is "better." As a hot-rodder you probably liked some cars with loud pipes and others powered by the same type engine with different sound.

I will just say that I follow what you are building and like the journey as much as the destination in each project.

Thank You again for your contributions to the hobby.

--ShopShoe


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## Brian Rupnow (Aug 27, 2018)

minh-thanh--Here is a link to the complete build.---Brian

https://www.homemodelenginemachinist.com/threads/a-new-engine-for-fall.23315/


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## machinejack (Aug 27, 2018)

Make a muffler  stuff it with a brass chore girl, rather like a heavy duty glass pack. Build one with a reservoir and add a drain plug to the bottom.


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## werowance (Aug 27, 2018)

brian, i have made homeade mufflers for generators and other briggs powered equipment similar to a glass pack muffler for a car,  big pipe for the outside casing, smaller pipe for the inside,  drill holes all on the smaller tube weld smaller tube with end plates inside the larger tube and pack all around with steel wool on the inside the weld up the other end plate.  made a huge difference on that last onan generator that was given to me for free but had a straight pipe on it that would deffen you when you fired that thing up.  wonder if that would do as good as the baffled approach you are using?


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## Brian Rupnow (Aug 27, 2018)

I won't build another muffler. This one was just a "what if", where I was bored and wanted to try something just to have something to do. My opinion is that yes, a muffler works, but doesn't make enough difference to justify the work required to build a muffler.


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## minh-thanh (Aug 27, 2018)

Brian Rupnow said:


> minh-thanh--Here is a link to the complete build.---Brian
> 
> https://www.homemodelenginemachinist.com/threads/a-new-engine-for-fall.23315/


Thanks Brian !


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## nel2lar (Aug 28, 2018)

Brian
I want to make a larger carb and looking at yours I would like to scale it up from your design. May I have the the file on it. 
Thank you 
Nelson


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## minh-thanh (Aug 28, 2018)

nel2lar said:


> Brian
> I want to make a larger carb and looking at yours I would like to scale it up from your design. May I have the the file on it.
> Thank you
> Nelson


A question that I also want to question


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## tornitore45 (Aug 29, 2018)

I made a muffler for the Lynx.  I wanted the in and out to be coaxial.

A pipe run through a larger pipe with the annular ring space between of the same cross section as the small pipe ID.   The small pipe is plugged in the middle.
A line of radial small holes is drilled from neat the input up to the plug, same thing from plug to outlet end bur 180* off.
Exhaust goes into small tube, through little holes, swirls around and forward to reenter the small pipe and out to atmosphere.

Never tried with and without to assess the attenuation, mostly for look.


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## minh-thanh (Aug 31, 2018)

This is for those who are interested :
https://www.homemodelenginemachinist.com/threads/model-i-c-carb-with-throttle.22799/
Thank you Brian Rupnow for sharing !! Thank you very much.
I will do it for my engine.


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## pkastagehand (Aug 31, 2018)

Exhaust noise much reduced, though as you point out in the video it leaves the mechanical noise more prominent.  Nice work!


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## Sprocket (Sep 1, 2018)

It's more of an expansion chamber than a muffler, but it sounds good, and this one was big enough to put a rain top on it. I've put these on all my engines, but the others were kind of small.
If it works, here are some pictures:









(Mechanically, this is the "Zero-6" from Model Engine Builder in 2006, but cosmetically it is nothing like the original)


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## nel2lar (Sep 2, 2018)

Brian
Mufflers have more good reasons other than noise, they produce a back pressure that can make a engine run better.
Thanks for all you do.

Sockets
I like that stand up pipe with the flapper on top. Very nice and a good looking engine.

Nelson


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## mrwolfe (Sep 4, 2018)

Have a look at O.S model engine mufflers. Not much to them at all, just an expansion chamber basically. Inlet and outlet have the same cross-sectional area with a fat tube in between. There is a 90 degree change in flow direction, not sure if that makes any difference. I think it's just there so the muffler doesn't stick way out to the side.


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