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  1. #1

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    How you do a free flow muffler?

    Hello Everyone,

    Yesterday I flew my 33cc weedeater conversion with a free flow muffler and it was great success.

    My engine achieves arround 600 RPM more and it was way more fun to fly. (8,000 RPMยดs with a 17x6 Falcon Prop at altitude of 2,240 metres (7,350 ft))

    But the free-flow muffler I was using was made of a plastic hose 90 degree elbow connector with some convenient ears to atach it to the exhaust, and of course it was melted with the exhaust temperature. (Picture attached)

    I know some of you made your own headers and mufflers for your conversions, could you share some pics of how you do them and with which materials.

    Thank you very much.
    Victor.
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    If I say that the Burra is Prieta is because I have the pelos in my hand.

  2. #2

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    RE: How you do a free flow muffler?

    This is what I need,,,,this kind of header to atach an aluminum elbow

    Anyone knows where i can get it? or something similar?

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    If I say that the Burra is Prieta is because I have the pelos in my hand.

  3. #3
    av8tor1977's Avatar
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    RE: How you do a free flow muffler?

    What I do is pry the seams of the original muffler apart to disassemble the muffler. I then take any and all baffles, soundproofing fiber, etc. out of the muffler, leaving only the piece where the muffler bolts go. That piece keeps the muffler from crushing when you tighten the bolts. If you want to leave that piece out too, you can make up tubes out of steel tubing to go where the muffler bolts go through. I then reassemble and re-crimp the muffler, and drill two holes for exit tubes. For a 33cc engine the tubes should be around 16mm inside diameter. I then braze (Soldar con bronce) the tubes in and it's ready to go!

    It is a little tough to undo the crimp to get the muffler apart, but it can be done. I use a sharpened screw driver to pry up the crimp a little at a time until I can get the muffler apart.

    Here is a pic of two of them done that way on my 50cc homemade twin.

    AV8TOR
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    If it is not SCARY, it is NO WHERE NEAR powerful enough!!
    All R/C planes have expiration dates---> It's just not printed on them anywhere!

  4. #4

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    RE: How you do a free flow muffler?

    I was flying with a guy a few weeks ago with a 2 bolt backplate 25cc Poulan that was flying a bit weak and very quiet, I told him to go home and split the muffler, wasn't good enough for him so we spent 15 minutes and did it at the field we just took the baffle and spark arrestor out and it really woke up the engine.

    Basically we just took some side cutters at the corners, screwdriver and pliers and it was apart, some quick hammer and plier work got the seam together again

    The header you have a picture of probably cost $100 or more if I had to guess, that tubing is a serious pain to weld...

  5. #5

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    RE: How you do a free flow muffler?


    ORIGINAL: rangerfredbob

    I was flying with a guy a few weeks ago with a 2 bolt backplate 25cc Poulan that was flying a bit weak and very quiet, I told him to go home and split the muffler, wasn't good enough for him so we spent 15 minutes and did it at the field we just took the baffle and spark arrestor out and it really woke up the engine.

    Basically we just took some side cutters at the corners, screwdriver and pliers and it was apart, some quick hammer and plier work got the seam together again

    The header you have a picture of probably cost $100 or more if I had to guess, that tubing is a serious pain to weld...
    No problem to weld. Tubing appears to be thin stainless steel. Use propane torch and some cadmium bearing blue tip silver solder.
    Usual rules, keep metal clean, plenty of flux, and watch you don't overheat or it will go black and then you have to start from scratch with new steel parts.

  6. #6

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    RE: How you do a free flow muffler?

    Yeah gut the muffler so its nice and loud, after you lose your flying field it won't be a problem.

  7. #7

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    RE: How you do a free flow muffler?

    My gutted mufflers with tubes are no louder than a modern home use chainsaw, half as loud or less than my old Mac 10-10 saw, I'd say most similar to my 25cc Homelite saw which is loud enough to sound decent but not loud enough to be annoying

    That and the OP is in Mexico, I don't think the people are as annoyingly anal as they are up here...

  8. #8
    av8tor1977's Avatar
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    RE: How you do a free flow muffler?


    ORIGINAL: rangerfredbob

    My gutted mufflers with tubes are no louder than a modern home use chainsaw, half as loud or less than my old Mac 10-10 saw, I'd say most similar to my 25cc Homelite saw which is loud enough to sound decent but not loud enough to be annoying

    That and the OP is in Mexico, I don't think the people are as annoyingly anal as they are up here...
    I'm in Mexico too, and this is one of the reasons why....

    AV8TOR
    If it is not SCARY, it is NO WHERE NEAR powerful enough!!
    All R/C planes have expiration dates---> It's just not printed on them anywhere!

  9. #9

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    RE: How you do a free flow muffler?

    You don't have be loud to have power. We lost our field because people weren't considerate enough to keep the noise level within guide lines.

    Gutted cans/chainsaws are above the AMA recommendation of 98db.In the middle of nowhere its not a problem to make noise, but you should consider your flying buddies may not like the noise.

  10. #10
    av8tor1977's Avatar
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    RE: How you do a free flow muffler?

    I'm certainly sorry you lost your field.

    However, my flying buddies and I LIKE noise. I'm often told my airplanes sound very "real" in the air. Luckily I live where noise is not a problem at my flying site. It is not even a problem at my home even though it is in a residential area here in Mexico. I test run engines at home all the time and never have complaints. Then again, when someone wants to have a street party until 3:00 am with loud music, I don't complain either.... (Actually when that happens, I always think, "At least somewhere it is still politically correct to party and have fun.")

    AV8TOR
    If it is not SCARY, it is NO WHERE NEAR powerful enough!!
    All R/C planes have expiration dates---> It's just not printed on them anywhere!

  11. #11

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    RE: How you do a free flow muffler?

    Noise and power output are almost always inversely proportional (except for explosions)

  12. #12

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    RE: How you do a free flow muffler?

    An expansion chamber with a muffler will be quieter than a gutted can or open exhaust and have much more power than you could achieve otherwise.On a 26cc engine power jumps from 2.8 hp to over 4 with a chamber, you will never get anywhere near this output any other way.

    Careful tuning with a specialty muffler will yeild more power and less noise than a gutted can.During my nephews foray into boats they used a specialty muffler, more power than standard muffler and reasonable noise level. I will have to find out what it was.


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