Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

Mini Pipe Section Drawing?

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Old 03-12-2008, 05:41 PM
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mmattockx
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Default Mini Pipe Section Drawing?

Does anybody have a section drawing of a mini pipe (Jett or Ultrathrust muffler)? I am just curious how they are assembled and how the folded wave pipe is set up and functions. Feel free to get technical, I am a mechanical engineer with a sound grasp of 2 stroke exhaust systems. I have just never seen a decent explanation of how the folded wave versions work. I don't want dimensions, I have no interest in making my own, for what Jett charge there is no way I can touch it on material alone, forget labor. I just want to know more details and WHY and HOW they function. Bob27, feel free to enlighten me offline with a PM if you prefer not to publicly explain.

Thanks,
Mark
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Old 03-12-2008, 11:44 PM
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Default RE: Mini Pipe Section Drawing?

Nobody? All these old time racers and speed guys and no one can help me out??

Mark
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Old 03-13-2008, 06:49 AM
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BillS
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Default RE: Mini Pipe Section Drawing?

Resonance theory in tuned pipes. My oh my what a question. Similar to 'How does the female mind work?' or 'Voodoo and other Magic.' The answers are not contained in a few paragraphs but are ambiguous and span volumes. Not surprising that no one attempted to answer.

But the book "Two Stroke Tuners Handbook" by Gordon Jennings would be a good place to begin. The book is out of print but I have seen it in web format sometime in the past two years. Additionally you might search the web for other similar information.

The subject is very interesting.

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Old 03-13-2008, 12:28 PM
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Default RE: Mini Pipe Section Drawing?


ORIGINAL: BillS

Resonance theory in tuned pipes. My oh my what a question. Similar to 'How does the female mind work?' or 'Voodoo and other Magic.' The answers are not contained in a few paragraphs but are ambiguous and span volumes. Not surprising that no one attempted to answer.
It's not resonance theory in tuned pipes, it's resonance theory in folded wave pipes. I understand typical expansion chamber systems very well. My problem is I have never seen a folded wave pipe drawn in section to have a look at how it is put together and how it works. Any diagrams/sketches/photos would be very helpful.

I have the Jennings book as well as several others (Blair is excellent, but heavy math if that is not your thing) and they don't really discuss this sort of shorty, compact pipe.

Yes, it is a very interesting topic with lots of black magic and voodoo surrounding it, as you say. The female mind is far more incomprehensible than wave action in a pipe, though...

Mark
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Old 03-13-2008, 12:57 PM
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Default RE: Mini Pipe Section Drawing?

I have seen pictures of them taken apart on this forum and thought they would have surfaced by now. Maybe it was daven that had them but not for sure.
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Old 03-14-2008, 12:58 PM
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Default RE: Mini Pipe Section Drawing?

Mark, why not just buy a Jett pipe and cut it in half? Cheap cost for all the knowledge you would gain.
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Old 03-14-2008, 01:12 PM
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Default RE: Mini Pipe Section Drawing?

It is basically just a tube with an appropriate cross section and volume which is cut to the appropriate length for the intended rpm.

If you are familiar with the way people build moose can pipes, it is not much different in theory. Similar too was the exhaust extractor used on the Formula 1 engines as well.

Key design work involves enclosing the device so it gets a bit quiet, and so it develops the best balance of backpressure for the engine.

And most important, the assembly of the muffler is rather involved. It took a bit of time for both Nelson and Jett to come up with assembly processes which stayed together. Dub's process has evolved to create a very robust assembly. Very rare one comes apart any more. About 1 a year

Bob
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Old 03-14-2008, 01:28 PM
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Default RE: Mini Pipe Section Drawing?


ORIGINAL: Kmot

Mark, why not just buy a Jett pipe and cut it in half? Cheap cost for all the knowledge you would gain.
Tom, I don't want to know that bad! If I buy a Jett pipe soon it will go on an engine, not into a band saw...

Mark
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Old 03-14-2008, 01:34 PM
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Default RE: Mini Pipe Section Drawing?


ORIGINAL: bob27s

It is basically just a tube with an appropriate cross section and volume which is cut to the appropriate length for the intended rpm.

If you are familiar with the way people build moose can pipes, it is not much different in theory. Similar too was the exhaust extractor used on the Formula 1 engines as well.

Key design work involves enclosing the device so it gets a bit quiet, and so it develops the best balance of backpressure for the engine.

And most important, the assembly of the muffler is rather involved. It took a bit of time for both Nelson and Jett to come up with assembly processes which stayed together. Dub's process has evolved to create a very robust assembly. Very rare one comes apart any more. About 1 a year

Bob
Thanks Bob. So the tuning length is simply the length of the inner tube and has very little to do with the outer casing details? Then you set the outer casing to cut noise and balance back pressure? I was under the impression from the name "folded wave" that there was some use of the internal length of the outer casing was used. Guess not. So this is just timed the same as any other 1/2 or 1/4 wave pipe, at approximately 1/2 or 1/4 of the full tuning length?

See, now I am glad that I asked. I thought there was something more intricate going on with the inner/outer casing design.


Thanks,
Mark
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Old 03-14-2008, 02:24 PM
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Default RE: Mini Pipe Section Drawing?

There is a little more to it, but primarily the stinger tube determines the tuning point.

There is a little to gain/tweek from the casing and the tail cone design. And the header/front section plays some part too in a balanced design.

The SS or 60LX muffler is a good example -- also the Q-500 muffler - note the bulge in the center section -- has to do with the expansion volume.

The tail cone has to do with the backpressure and exhaust gas velocity, and there is a component of that "folded" pipe you noted.

Some may wish to note..... the exhaust opening is less that 1/4" ..... sometimes big gaping exhaust is not the right answer.
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Old 03-14-2008, 04:17 PM
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Default RE: Mini Pipe Section Drawing?

Here's a quick drawing I did in TurbaCAD based on Bobs description.

It truly looks like a folded tuned pipe to me. The Sound wave travels down the inner pipe, bounces off the back cone, bounces off the front cone, bounces back off the back cone again and back down the inner pipe to the exhaust port. The outlet can be anywhere in the can, it just happens to be in the back because that's the easiest place to machine it. The outlet diameter and length controls the pressure in the pipe and the heat of the engine.
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Old 03-14-2008, 04:19 PM
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Default RE: Mini Pipe Section Drawing?

ORIGINAL: bob27s
Some may wish to note..... the exhaust opening is less that 1/4" ..... sometimes big gaping exhaust is not the right answer.
Thanks for the details, Bob. I just wanted an overview as to how and why they worked and you have given me that. There is almost always more to it than meets the eye, as you say, but the basic mechanics of how it works is what I was after.

I have to say that a big gaping exhaust is almost never the right answer, especially for a 2 stroke (and even in 4 strokes, truth be told). In the late 90's - early 2000's the Honda NSR125 roadracing motorcycle (125cc, liquid cooled, very highly developed) had an internal lip where the end stinger met the converging cone on the exhaust. If you looked at it, the lip stuck in noticeably and probably reduced the stinger sectional area by 10-15%. Of course, tuners looked at this and thought it was a travesty of flow restriction. They removed it and promptly lost around 3-4% hp. Doesn't sound like much, but that is a huge gap to give up in an ultra competitive class like 125GP. I guess Honda meant it when they put that lip in the pipe...

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Old 03-14-2008, 05:11 PM
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Default RE: Mini Pipe Section Drawing?

OK, I did the whole series. I'm just getting into using CAD for anything other than IC design. I really like it.

1. The sound wave travels down the inner pipe.
2. Bounces off the back cone.
3. Travles down the outer pipe to the front cone.
4. Bounces off the front cone and travels back towards the rear cone.
5. Bounces back off the back cone again.
6. Back down the inner pipe to the exhaust port.
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Old 03-16-2008, 12:59 PM
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Default RE: Mini Pipe Section Drawing?

I build my own mousse cans, have Jett and Nelson mini pipes. I've had the internal pipe on a JETT come loose and had to reassemble.
Talking with DUBB he told me that it had threads on outer can and inner pipe in conjuction with green locktite.

I made a outer sleeve with 1/4" wall thickness with a slit lengthwise to clamp it up on the outer can in a lathe chuck. I then heated threaded front area while hand spinning lathe chuck. Once you smell that locktite smell and smoke it unscrews easily.

In rc combat I would run the mousse cans on my Jett 30 because they were over an ounce lighter. Mousse cans are just insane simple and work so close to stock machined ones its sick.
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Old 03-16-2008, 09:04 PM
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Default RE: Mini Pipe Section Drawing?

Hi c/f.
I saw a build thread for those mousse can pipes once but lost track of it. Would you have a link for that? I would love to learn how to build those.

Thanks Terry
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Old 03-16-2008, 10:12 PM
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Default RE: Mini Pipe Section Drawing?


ORIGINAL: ChrisAttebery

OK, I did the whole series. I'm just getting into using CAD for anything other than IC design. I really like it.
Thanks, Chris. That was something like I had imagined and the number of reflections is correct to give a suction pulse back at the port on the first reflection. It would seem it's a combination of the stinger reflection wave and the "folded wave" component as you have drawn up.

S4G, have a look at this site:

http://webpages.charter.net/rcfu/ConstGuide/MCM.html


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Old 03-16-2008, 11:36 PM
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Default RE: Mini Pipe Section Drawing?

Terry the trick is to come up with a mouse can with threads. Using a Macs header pipe for particular engine, you just slide silicone coupler over header, then screw on can over the silicone, this is all thats needed to hold can securely, Then some 1/4" or 5/16" aluminum tubing makes for an exhaust by gluing it into can with JB weld in center or side as needed . I flare the tube end and put JB weld on flare and insert via inside of can center then add fillet external.

You can actually start with the header at its longest length and it generally is within 3/8" - 5/8" from rear of can, then run and tune, then cut an additional 1/2" off header, run retune to this range from rear of can. The can is no science its just tuning it to what you have to work with.

On Webra .32 the cans can add minimum 1500rpm with poor tuning and 2000+rpms with optimal tuning if you keep at it.

Generally speaking a .25 motor worked on a shorte pipe than did a .32. .40's were longer yet.

Don Miller of AL, is the inventor from competition fun fly days and gets the cans, The article you may refferance is a differant home brew in which cans without threads are used. The MAc header is the costly part of Dons setup which is all I used.

Don hangs out at RCG under the nickname Miderror
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Old 03-17-2008, 05:34 AM
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Default RE: Mini Pipe Section Drawing?

There you go. The inside of a Nelson muffler.

Ed S
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