Can a muffler be tuned like a pipe, of course it can.

I read the OS 20 discussion and thought I would way in on the tuned muffler controversy. We have worked with tuning mufflers for 20 years. Mostly it started in Racing and the first one came form Australia. At that time it was nick named "The Magic Muffler" and we all we very interested in finding out how it worked and how to make it work in our racers. It was shelved as not doable in the early 80s as our event did not allow it at the time. Henry Nelson was the first to make them available for Q500 racers in the late 80s early 90s. It was awesome to say the least. Q500 airplanes began to rival the premier event of Formula One with all of it's fire breathing no holds barred high nitro engines and the Q500 were limited to stock props, engines and 15% nitro. The mufflers were truly acting within 10% of a full tuned pipe on nitro! Q500 was going so fast that it was moved to the long course with F1 and the time difference for 10 laps was only 3 to 6 seconds. This really was the beginning of the end for F1. QM40 was born with the same muffler only in F1 type planes and it also became very fast very quickly. So quick that it has been slowed down twice with venturi limitations and all on 15% fuel and now even APC stock props recently. This type of muffler does need to be operated in it's element as RPM is very important and does not seem to work in the lower ranges. Dubb Jett went to work in the early 90s,after starting Jett Engineering, and needed this to work in regular R/C engines for the Sport flyers that wanted lots of power but did not want to run 18,000 RPM. Many years of hard work has rewarded him with some of the most powerful engines on the market for R/C. A lot of the credit goes to his tuned "mufflers".

After much prodding from me that there was a vast market for an in-cowl muffler for all of the scale planes available to the R/C crowd he began to think about it. One thing you need to know about Dub is he has many patents to his credit in the oil field business from working for Baker Hughes till he retired and starting Jett Engineering. He wanted the muffler to boost power not just fit in the cowl. He did such a good job of it that the Government awarded him a patent for his effort as well as buy them from him for RPV work. It took a while to design one for Gas and low RPM but he got it done.
In our work with the RO-Jett's we wanted the RE muffler to take as little RPM off as possible. We new from our experiences with other areas that any exhaust can be maximized and even tuned in some cases. The RE muffler that I make for the BSE 40 actually adds 200 RPM over open exhaust. Even with all of our experiences with this type of work we were surprised. With the real tunned mufflers (Jett calls the Jett Stream)it not to hard to get as much as 30 to 40% power increase. With the incowl muffler we are seeing 10 to 20% (mostly because of the lower RPM that it is used at).

Over all what I am saying is that exhaust systems can be optimized when using what you have or designing for what you need. I believe that Brett found that OS (this is my own opinion on this part) stumbled onto the right muffler for the engine when used the way Brett set it up. I am sure that OS did not intend for this to happen as the engine is designed for R/C use. Now before you ask why are we not running tuned muffler in Stunt let me say I do not think you would want to. The system is a littler on the large side and somewhat heavy. It is no more than a tuned pipe but is all up front where it is unsightly or to large. I have included pics and stats to illustrate.
Richard Oliver
Jett-Stream Muffler Comparison Data - Sport Jett .46

Prop Size (APC)
Stock OS Muffler
Jett-Stream Muffler
Turbo-Jett In-Cowl

10 x 6
14,700 RPM
16,700
15,800

Jett-Stream Muffler Comparison Data - OS .46

Prop Size (APC)
Stock OS Muffler
Jett-Stream Muffler
Turbo-Jett In-Cowl

10 x 6
14,200 RPM
15,900
15,400

Turbo-Jett In-Cowl Muffler Test Data - GMS .40

Prop Size (APC)
Stock GMS Muffler
Jett-Stream Muffler*
Turbo-Jett In-Cowl

10 x 6
13,100 RPM
---
14,200

11 x 6
11,000 RPM
---
11,900

11 x 8
9,400 RPM
---
10,500

WOWIE-ZOWIE-- Paul-

Maverick,

All during the 20FP discussion I would sometimes consider bringing up the points you make. I am now glad that I never did, as you have much better numbers and input. Thanks.

>need. I believe that Brett found that OS (this is my own
>opinion on this part) stumbled onto the right muffler for
>the engine when used the way Brett set it up. I am sure that
>OS did not intend for this to happen as the engine is
>designed for R/C use. Now before you ask why are we not
>running tuned muffler in Stunt let me say I do not think you

Richard;

Good stuff. Thanks for sharing the hard data with us.

My exposure to tuned pipes on 2 strokes is long but thin. One of the aspects that I remember is that to get a consistent "pulse" or reflected wave back to the exhaust port that could be timed to maximize exhaust gas ejection and minimize fresh fuel air ejection, we needed a "smooth" or obstruction free chamber. That was why all of the headers that were side mounted gradually wrapped around rather than taking a hard right angle. Even 1/2 or 1/4 wave mufflers like the MACS 6650 have the gradual turn to the rear, minimizing the possibility of creating an additional set of reflective waves. Straight rearward exhaust was preferable, as it minimized possible conflicting wave forms in the exhaust.

Let's take the FP 20 muffler as an example. The exhaust exits the engine, travels about 1/2" or so, and then turns almost 90 degrees as it hits the side of the muffler. I am sure there is some wave reflection at that point. As the exhaust gas exits, it passes through/over/around a baffle, causing another reflected wave, and finally hits the taper at the end leading to the exhaust tube, which generates a third. Seems like a lot of conflicting wave forms to have a tuned pipe effect.

I have not used a Jett muffler, and do not doubt their effectiveness and quality. Again, though, there is the right angle turn from the exhaust.

So my question is how can we have the tuned pipe effect from a conventional muffler, e.g. the relected wave that maximizes exhaust is evacuated from the engine but minimal fresh charge escapes with what appears to be a setup that results in at least two of more wave forms?

Just curious. I hope someday I will have the scratch and the justification to own an RO Jett engine.

V/r

Hi Bob, When Brett was describing his pipe effect it can only be characterized as "effect". When the conditions are right it will happen. The 90 degree turn has never been a issue in our design work. Rear Exhaust never showed any more power than Side Exhaust. In my post about tuned mufflers I did not explain all of the workings of the dynamics of what is happening. Some of what you get with a short muffler is acoustic and or others are fluid. I can only guess at what you are describing with the bend is that the chamber is causing a vacuum for the gases and they do not care if it is also 90 degrees. They are seeking someplace to go and follow the chamber. Now if the back of the chamber is in the right place for a reflected wave or an acoustic bounce then things happen. You may even get the fluid bounce to meet the acoustic bounce(which may be off the front wall) at the right place and cause a charge to enter the now opening exhaust port. That is about as simple as I can keep it.
Oh, and look forward to having you as a customer, someday? I have a couple of my personal engines in the classifieds if you are interested.
Richard Oliver

So I've been thinking, in my hot rodding days, the one thing that was consistent in most configs was the positive effect of A/R (anti reversion) cones in the exhaust header. It always benefited the low end torque. (and my buddies loved them in motorcycles to.)

Is this effect unique to larger 4 strokes Has anyone experiment with them with our engines?

>Let's take the FP 20 muffler as an example. The exhaust
>exits the engine, travels about 1/2" or so, and then turns
>almost 90 degrees as it hits the side of the muffler. I am
>sure there is some wave reflection at that point. As the
>exhaust gas exits, it passes through/over/around a baffle,
>causing another reflected wave, and finally hits the taper
>at the end leading to the exhaust tube, which generates a
>third. Seems like a lot of conflicting wave forms to have a
>tuned pipe effect.

The turn wont have a negative effect on it once the system is running and in the "tuned" range. Remember the acoustic wave is really the one giving the pipe effect. Once the right acoustic wave is reached inside the pipe the travel and the turns it makes really have no effect. It is all particles just banging into one another making it work. One particle bounces off one next to it and the one next to it gets bounced and so on. Like a long line of ping pong balls tap one on one end and the one on the other end flys off of the line. Now line those up in a hose where they can easily travel inside but not get out of alignement and bend that hose in any direction you like and tap on one end and the other one on the other end will still bounce out just fine. It is an instantaneous reaction from end to end. This is how the wave reflection works. It actaully bounces from end to end through the particles in the air. This is how come you can make twists and turns with the pipes and have no ill effect. I once ran an FP 40 on a R. Smith resonator pipe, four chambers. I used a side exhaust header and ran the pipe down the side of the plane. It worked great. Got a nice pipe rattle and great performance. Then I got a wrap around header and it ran exactly the same. Then I got a tube muffler. I was able to get a tuned pipe run, however it was at a different rpm and on a different prop. Being a muffler I could "tune" it. The length is dictated by its construction. But it did work really well.

Notice on the OS muffler and the Jett one for that matter the exit is not directly away from the exhaust port. It looks more like it is off center or randomly placed off to the side. This is key I think. It lets out gasses but keeps in waves that are reflecting from end to end. Thus you have the tuned effect. You can prove it out on the bench real easy. Once you get a tuned effect you will hear a distinct rattle. A very noticable off beat out of time rattle that seems to have no rhyme or reason to it but it is there. It very evident when using OS mufflers when the motors are in a full 2s.

>
>I have not used a Jett muffler, and do not doubt their
>effectiveness and quality. Again, though, there is the
>right angle turn from the exhaust.

See above.

You will note on the OS mufflers the entrance into the muffler is back a bit from the front and the exit is forward a bit from the rear. (my own thoughts here) Now that is how gasses get in and out without effecting the waves in the big chamber. Get those waves really bouncing inside there and they charge up the chamber creating an enourmous amount of positive charge and the cylinder gets charged up also.

Also, next time you are in a convenience store pick up a motorcycle mag for dirt bikes. They have some real funky twisted and turned tuned pipes for their bikes. Yet the waves are trapped in there and they are very effective. The pipes are built to charge the motor in certain rpm ranges. Most race apps have it so that only at 90% of full throttle and up does the pipe really come in and put the motor in full power. Run it under this throttle setting for long and you will foul off your plug. Gets expensive at 7 bucks a piece...ask me how I know...

>
>So my question is how can we have the tuned pipe effect from
>a conventional muffler, e.g. the relected wave that
>maximizes exhaust is evacuated from the engine but minimal
>fresh charge escapes with what appears to be a setup that
>results in at least two of more wave forms?

The key to answer your question would be to be able to see OS's testing and see a model of how the waves actualy reflect inside the muffler. That would really answer your question. Now finding that info....I dont know about that. But the simple fact that you can hear it happening should be some indication of what is going on.

>
>Just curious. I hope someday I will have the scratch and
>the justification to own an RO Jett engine.
>
>V/r
>
>Bob Kruger

LAST EDITED ON Mar-31-04 AT 06:47 AM (CDT)
 
>
>The turn wont have a negative effect on it once the system
>is running and in the "tuned" range. Remember the acoustic
>wave is really the one giving the pipe effect. Once the
>right acoustic wave is reached inside the pipe the travel
>and the turns it makes really have no effect. It is all

Doug;

Not sure I agree with that. Lets start off with a couple of givens: The first thing is that the pipe length is adjusted for a given RPM range. So, we set the range. Secondly, no energy wave cleanly makes a hard turn, whether it is sound, electricity, water, etc. Finally, any wave pattern that hits an object in its path will set up a relective wave of some sort.

>particles just banging into one another making it work. One
>particle bounces off one next to it and the one next to it
>gets bounced and so on. Like a long line of ping pong balls
>tap one on one end and the one on the other end flys off of
>the line. Now line those up in a hose where they can easily
>travel inside but not get out of alignement and bend that
>hose in any direction you like and tap on one end and the
>other one on the other end will still bounce out just fine.
>It is an instantaneous reaction from end to end. This is
>how the wave reflection works. It actaully bounces from

No argument there. The key to remember is that the flow is follows a straight or curving surface. In the OS type muffler, you have an exhaust stack exit and a hard right turn into the expansion chamber. The exhaust flow is not a gentle bend. So, you are going to set up at least one wave pattern there. Then the exhaust has to pass through a baffle that may or may not set up a second wave form. Finally, it gets to the end of the expansion chamber and we have a third wave form.

You description above is accurate. Now, take that hose and put 90 degree bend in it, and see what happens. Even at 80 degrees you would have problems. Put baffles in it and see what happens. Lots and lots of conflicting wave patterns. That is essentially what I see in the OS style muffler.

Note - I have seen some exquisitely made tuned pipes for two stroke motorcycle engines. The makers went to great care to make the bends as gentle as possible to minimize or eliminate creating additional wave patterns. Even a simple pipe like the MACs 6650 has a gentle rearward curve and no baffles. I am sure the designers did that because they knew that additional wave forms would results from the reflections off of any obstruction (like a baffle), or from any harsh turns (like the exhaust stack to expansion chamber).

Now, I have played a good bit with OS Mufflers on FP 25s, 35s, and 40s trying to reach this near nirvana that you write about, and have not gotten there. This includes numerous prop and fuel setups, with and without the baffle. I honestly think the Max 40 muffler too short for this effect. However, if it was lengthened and the baffle removed, there might only be two wave forms, and if the exhaust stack to expansion chamber generated wave form is small enough, a type of pipe effect could result.

>around header and it ran exactly the same. Then I got a
>tube muffler. I was able to get a tuned pipe run, however
>it was at a different rpm and on a different prop. Being a
>muffler I could "tune" it. The length is dictated by its
>construction. But it did work really well.

Interesting. Did you remove the baffle?

>Notice on the OS muffler and the Jett one for that matter
>the exit is not directly away from the exhaust port. It
>looks more like it is off center or randomly placed off to
>the side. This is key I think. It lets out gasses but

Angle on the one I am holding here is about 83 degrees. Yes, it is off center to the chamber. Hmmmm. This might mitigate a returning wave pattern.

>keeps in waves that are reflecting from end to end. Thus
>you have the tuned effect. You can prove it out on the
>bench real easy. Once you get a tuned effect you will hear
>a distinct rattle. A very noticable off beat out of time
>rattle that seems to have no rhyme or reason to it but it is
>there. It very evident when using OS mufflers when the
>motors are in a full 2s.

I have tried this, but have not gotten your effect.

Question - what is your setup?

>Also, next time you are in a convenience store pick up a
>motorcycle mag for dirt bikes. They have some real funky
>twisted and turned tuned pipes for their bikes. Yet the

See above. My first experience with tuned pipes was two stroke motorcycles.

All good stuff, Doug. I look forward to seeing your setup data and trying it out myself. I may also experiment with some aluminum tubing cut at certain lengths to vary chamber length to see if this effect occurs at different RPMs. If it does, then your theory that we can get a pipe effect from a standard OS muffler is valid.

V/r;