Exhaust Systems

[carey shurley]

Because of the displacement difference between most gas motors and most nitro motors, the nitro purposed mufflers can't be used, you need capacity for much greater exhaust volume that the gas purposed mufflers provide

As you've probably noticed, there are a number of exhaust systems available for gas helicopters. Its often hard to decide what system you might want because you won't likely be able to compare them at your local field and some of them are pretty expensive so you wouldn't want to buy them all to compare.

So the point of this thread is to compare some very common exhaust systems, see how they mount, compare weights/costs and actually hear them perform.

What I'm going to do here is show you five common exhaust systems, provide some data about each, show them side by side and then let you hear them on the same model, at the same RPM.

The Mufflers

Zenoah

First up, the standard Zenoah muffler, often referred to as a "can" muffler. Its of steel construction and the lightest of all of these. Its also the cheapest


A stock Zenoah "can" muffler

as you can see its a pretty simple design.

Zenoah Muffler mounted

The Zenoah muffler is simple to mount with only two bolts. Over time I've found that the engines will perform acceptably using this muffler. They measure 3" x 4", weigh 5.8oz and sell retail for $10, however as you'll hear it has a HORRIBLE exhaust tone. Its by far the loudest of all of these mufflers so in this case you get what you pay for.

Century

Next up, the Century Torpedo muffler. Its of all aluminum construction and the second lightest muffler.


Century Torpedo Muffler

This muffler is the longest of the group. Its diameter is about the same as the Zimmerman but smaller than the RJX or Hatori


Century Muffler mounted

The Torpedo mounts with two bolts but now comes with a secondary support that attaches to the rear of the muffler. This would have to be mounted to the aircraft frame somewhere. I didn't install it for these tests.

For my ears, its the second loudest pipe of the bunch. It doesn't have the same annoying raspy sound of the stock muffler however its quite loud. I know a number of people using these with good results. In my case I've found that its one of the two mufflers that can cause the engine RPM to hunt at very high RPM. From my experience if you turn your motors 13K RPM or less it seems to work fine. 14K and over and it caused an engine RPM wag thats not mixture correctable nor governor exaggerated. Something to keep in mind with your setup

Zimmerman

Next is the Zimmerman 2653, which is side exhaust muffler. Its the only one of this group thats constructed of stainless steel. As you can see over time as it heat cycles the metal takes on a bronze tone. As a result its about 30% heavier than the all aluminum Torpedo


Zimmerman 2653 Side exhaust muffler

The Zimmerman is roughly the same length as the RJX and Hatori mufflers but is similar in diameter to the Torpedo


Zimmerman Muffler mounted

This muffler mounts with only two bolts. Because its made of stainless its quite durable and seems to hold up to vibration without any problems.

One additional note about this muffler, its the only one that exhausts out the side. The good news is that it works fine on either left or right side mountings. The bad news is that the exhaust stack sticks out about 2" and has quite sharp edges. I've ripped open my leg more than once with it so be careful how you carry your model if you use this.

From a sound perspective, its about middle of the bunch. It has a pleasant tone but its the other muffler I've found that can cause the engine RPM to hunt at very high RPM. At RPMs of 14K and over and it caused an RPM wag thats not mixture correctable nor governor exaggerated. Again something to keep in mind with your setup

RJX

Next is the RJX, which is the newest design of this set of mufflers.

Its roughly the same diameter and mounting dimensions as the Hatori (in fact it will mount on the same exhaust plate) but is the shortest of all of these (other than the can) and is all aluminum construction. Its the heaviest of all of these but is also the second lowest cost.


RJX 90G Muffler

This muffler is different from the Zenoah, Century or Zimmerman in that it mounts to a steel exhaust plate that is bolted directly to the cylinder. The muffler then mounts to this steel plate. The reason for this is to better deal with thermal expansion. Since Hatori originated this idea I'll cover it with that muffler


RJX Muffler mounted

It requires two bolts to mount the exhaust plate, two bolts to attach the muffler to the plate and two more bolts to support the muffler against the steel plate.

In my opinion, its only slightly louder than the Hatori and has a pleasant sound. It didn't cause any odd engine behavior and didn't come loose. Because its relatively new I do NOT know how they hold up over time against vibration.

Hatori

The final muffler I looked at is the Hatori. Its considered the cadillac of these mufflers. Its by far the most expensive. It is however very well made and will not crack over time.

It was designed to deal with very high exhaust volume for high RPM use of 23 and 26cc motors so its large. Its also the second heaviest.


Hatori 956 Muffler

The muffler comes in two versions the 956 and 957. The 956 (shown) is for front mounted engines and usually mount on the left side of the model. The 957 (also known in the US as the SAB-12-2R) is for rear facing motors and usually mounts on the right side of the model

The original version of these mufflers mounted directly to the cylinder. This version suffered from thermal expansion problems and was practically impossible to keep on the model. Later the design was changed to include a thick stainless steel plate that mounts to the cylinder. The muffler then bolts to that plate. This has proven to be a durable and reliable setup.


Hatori Muffler mounted

In my opinion, this is the quietest of these mufflers. I have never had any performance or motor operation impacts when using these. They seem well suited for both low, medium and very high RPM operation.

Stacked Up

To give you an idea of the relative size of these mufflers, I stacked them next to each other. You can see that the RJX is the shortest and the Century is the longest


Mufflers Compared Side by Side

However because of where the cylinder mount is located within each muffler the weight distribution of each of these is very similar. I also compared their weights, costs, dimensions and material.

• The clear winner on cost and weight was the Torpedo it is however quite loud
• In my opinion the clear winner on overall sound and consistent performance is the Hatori. The newest version has the largest internal volume of any of these pipes

.

For your Ears

I had intended to measure their decibel levels of each of these mufflers with my Android phone from the std 10 meter distance, however my EVO is limited to 82 decibels. All of these are louder than 82 decibels. Nonetheless listen to these videos, it will give you a good idea how each sounds

With this video I looped the high RPM operation of each of the mufflers a couple of times so you can hear them compared against each other. In each case the exhaust was pointed at the microphone.


A Quick Comparison of Muffler Sounds

This video has a more complete test where I compared the sounds of each muffler in four different orienations to the microphone at both hover and high speed operation. This should approximate the sound they would make on your model in various flying positions.


Full Comparison of Muffler Sounds

The Dark Side

So far I've only discussed mufflers. There is another element of exhaust systems for gas helicopters and that involves fully tuned pipes or expansion chambers.


The alternative - Tuned Pipes

These things have proven to add 2 or more horsepower to a motor where the port timing has been matched to the design of the tuned pipe

as you can see, these are very similar to those found on gopeds, go karts, and motorcycles they are just smaller. Unfortunately they also need to be quite long so they are hard to mount, induce a lot of air drag and are easily damaged in a crash

They also typically make the motor peaky and hard to tune. As a result these have not been terribly popular on model helicopters. This may change in the future however as new pipe designs become available

The Bottom Line

• There are a good variety of exhaust systems available for your model helicopter. They come in different weights and costs and produce varying levels of sound
• Some of them can also negatively impact the operation of your motor depending on how fast you turn your motor
• If you're using a tuned engine, follow your tuners advice on which muffler will work the best with your particular setup. Due to the nature of performance modifications its possible that your choices may be limited.
• The Hatori remains my favorite, although the most expensive its virtually guaranteed success. I have yet to have one crack or have anything inside come loose. It also has the largest volume for todays larger displacement motors.

[rbort]

A+!!

-=>Raja.

[dar61]

Big Thanks!

[kopterkat]

As always very complete and to the point.

[Rototerrier]

I thought the RJX sounded pretty quiet and had the deepest tone. What do you think?

I believe the Century V4 has the deeper sound like this as well. Another reason I prefer to run it over the Century V2. The V2 is very loud to me. Of course, nothing compared to the stock can...but that's a given. There isn't anything to that can.

[carey shurley]

The RJX definitely has a pleasant tone. Its a little heavier though. I also have no long term experience with it in terms of longevity. It may be fine, I just don't know. My concern is always about cracking and having stuff inside come loose. I know the Hatori's are very durable so I'm sticking with them.

[Justin Stuart]

Nice article.

[Rototerrier]

Originally Posted by carey shurley

The RJX definitely has a pleasant tone. Its a little heavier though. I also have no long term experience with it in terms of longevity. It may be fine, I just don't know. My concern is always about cracking and having stuff inside come loose. I know the Hatori's are very durable so I'm sticking with them.

Well I can vouch for the Century V2 cracking. My original cracked on me. Fortunately, it wasn't too much trouble getting a replacement. Century did make me email some photos and they said it didn't appear to be cracks and that they probably wouldn't replace it.

I said...they are cracks and I am sending it in anyway. Sent it in and got a new one back a week later. They tried to mess with me a little, but in the end it all worked out. The replacement has been holding up just fine.

I don't let it bother me too much though. I had a Thunder Tiger Red Line 3D break in half, a crack formed in a Hatori SB19, and the baffle came loose inside an Align 50. All replaced under warranty except the Align.

I have had nothing but bad luck from pipes. So far, the only pipe model I have not had break on me is the second hand Century V4 I picked up in the forums and It is my favorite.

This is a VERY GOOD article. I love being able to hear the different pipes back to back to back. Good stuff

[helipainter]

awesome post! I too have the v4 on a g26 and mine too sounds most like the rjx in the video. Think it has the 10mm tip, pretty sure it is tunable tips but am just using what it came with.

[Jeff396]

May my RJX rest in peace It didn't break off completely in the air. It was hanging by about an inch of metal around the diameter of the can at a 45 degree angle. I realize these gassers can vibrate a bit but you'd think the mufflers would be made a bit more robust to stand up to it. Oh well, no idea what to get now. I may just annoy people with my stock can until I get through my grieving process




Jeff

[Mega325]

Very nice but I do not agree that a tuned pipe makes a motor hard to tune. I see no difference in tuning a motor with a muffler or pipe. maybe it is just experience. I would say that if you use the stock zen muffler take it a pair of needle nose pliers and pull the stuffing out. you will get an increase in power but will also get an increase in noise. that is all relative to what you consider noise. i think it is music myself. or you can get a tgn track pipe that will give a little boost. they are very well made and not much bigger than a stock muffler.

[Doozer]

Hi Carey,
If you ask me, the RJX sounds the quietest and has the best tone but that probably just me. Hopefully mine stays together. Awesome thread! Thanks for all that you do.

[bullitt]

Thanks for the great information and recordings Carey.
You mentioned that century provides a rear mount for their torpedo.
I purchased the torpedo from century helicopter about the same time you posted this and I didnt recieve a rear mount.
Could I bother you to post a photo of the mount so I could fabricate a close variation to fit my bergen.
If I saw this post before I made my purchase I think I would have gone with the rjx.
Who stocks the rjx just incase I want to pick one up?
Thanks again for all the great gasser information!

[carey shurley]

the additional support is listed as century part #CN3071A

[sps3172]

Carey,

Do you know of a domestic source for the Hatori 956? I've only been able to find the 957.

Thanks!

[carey shurley]

heliproz should be able to order it for you

if not email hatoriusa@aol.com

the latest version has quite a bit more volume than they used to

[Doozer]

Originally Posted by bullitt

Thanks for the great information and recordings Carey.
You mentioned that century provides a rear mount for their torpedo.
I purchased the torpedo from century helicopter about the same time you posted this and I didnt recieve a rear mount.
Could I bother you to post a photo of the mount so I could fabricate a close variation to fit my bergen.
If I saw this post before I made my purchase I think I would have gone with the rjx.
Who stocks the rjx just incase I want to pick one up?
Thanks again for all the great gasser information!

http://helidirect.com/rjx-gas-muffle...cc-p-20877.hdx

[Doozer]

While were on the subject of RJX pipes... there are four holes in the pipe itself and two in the exhaust plate, but the pipe on comes with four screws. I understand that I have two for the stock exhaust, but they are way too long. Am I missing something here? What are the other two sets of holes on the pipe for?

[carey shurley]

there are four holes in the exhaust plate. Two non-threaded which the bolts that attach it to the cylinder goes through. The other two are threaded and are what the muffler itself bolts to

the muffler has two holes on the outside of its flanges, they bolt the muffler to the exhaust plate. The other two are lateral holes used for side support. 4mm bolts go through these with large flat washers. The washers are big enough that they extend across both part of the muffler header and the exhaust plate. The entire mounting system is an almost exact copy of the Hatori muffler which originally introduced these mounting methods.

[prototype3a]

Do you have any opinion on the old Bergen "unobtanium" pipe?