Jett Stream Muffler for Magnum .91  
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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Engine Manufacturers Direct Support Forum >> Jett Engineering Support >> Jett Stream Muffler for Magnum .91
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Jett Stream Muffler for Magnum .91 - 9/11/2004 5:49:02 AM   
AdrianM


 

Posts: 702
Joined: 10/8/2002
From: Palm Harbor, FL, USA
Status: offline 		I have a Magnum XLS .91A. It an OS .91 clone but its ABC not Ring. I want to get a Jett Stream muffler for it but I see there are 2 different ones available. I will be running it in a .90 size pattern plane and the designer set up the thrust lines for a .91 2 stroke turning a 14x8 prop. My Engine will spin an APC 14x8 ~10000rpm on 15%. Which pipe should I get? What kind of gains should I see at this lower RPM?

What kind of throttle response will I get with a Jett Stream. I need it to be very linear. I don't want to get one if I will be getting an on the pipe off the pipe feel.

Thanks in advance!


_____________________________

Adrian Martinez
       Post #: 1

RE: Jett Stream Muffler for Magnum .91 - 9/13/2004 4:37:05 PM   
bob27s



Posts: 4833
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: online 		Adrian,

Thanks for writing. I left a bit of a long explaination in the 3D forum where you had posted earlier.

If you can show/tell me which aircraft the installation will be used in, I can help a bit more.

RPM wise..... the OS91FX we did a lot of testing on, ran very well with all of the mufflers we tested. As you noted, the Magnum is not off by much in power (if at all). Although, I can not find rpm numbers for a 14x8. On the Jett-stream, the OS91 turned a 14x6 about 11.5K and a 15x8 just a hair below 10K rpm. This was roughly a 800-1000 rpm increase over the stock OS muffler. At these prop sizes, thats a big increase in power and thrust. In the 90 size mufflers, taking into consideration assorted variables, we typically will claim an rpm increase of 800 rpm on average, above the current rpm with the stock muffler.

The Jett-Stream 90T muffler is basically tuned for the 9000-12000 rpm range as used on our 1.20 engine ( i have to double check my notes here, but I am pretty sure this is what we did the rpm tests on the 91 with using the bigger prop). Better in the lower power band, it runs very smooth, with no huge jump in power as the muffler stages since it stages at a lower rpm. You will see a bit less of an RPM gain (500-600) , but you will be able to load a bit more prop on the engine, and still keep it up in that 9500-10000 range. Runs more like the turbo-jett muffler installation.

Using Dubs SJ-90L with the long muffler.......... the combination runs quite a bit like my old Hanno 61 with the 650 Hatori pipe set up long. Smooth power, and didnt stutter at the pipe stage because it was fairly broad range...but you could notice the jump going vertical. Using the real 'hanno' pipe, there was no noted step at all.....had a longer forward chamber.

The OS and Magnum 91 engines respond the same way with the 90T muffler.

The OS91FX we tested ran especially well with the Turbo-jett muffler installed. The nice thing is they also run best on our 10cc version. My BSE-100 and 120 require the larger 15cc turbojett. So the 91 installation is a bit more compact. This might be an option if you have enough room up in the cowl area. VERY broad power band, still turns a 14x6 at 11.2K rpm (yes, we noted this was a significant sweet spot.. ran about the same with either muffler). It turned the 15x8 at about 9500 rpm.......... so sticking with your 14x8 should get you somewhere in the 10,800 range.

The turbo jett tends to be quite too. For reference, my BSE-1.00 with the turbojett, turning a 15x8 at 10,200 peak rpm, I measured sound readings around 85 dba at 10 feet (radio shack meter, over grass, Aeroworks Edge 540 installation).

Let me know a bit more about the specific application, and I can assist you a bit further.

Bob


_____________________________

Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host

(in reply to AdrianM)
       Post #: 2

RE: Jett Stream Muffler for Magnum .91 - 9/13/2004 7:11:30 PM   
AdrianM


 

Posts: 702
Joined: 10/8/2002
From: Palm Harbor, FL, USA
Status: offline 		Bob - Thanks formall the info. The plane is a CA Model Epsilon. The plane's thrustlines are set up a .90 2 stroke and a 14x8 prop. It is a Pattern/Artistic Aerobatics (3D) plane.

Wing span: 63"
Fuse: 65"
Weight: 7-8lb




I would like to use a long Jett Stream but as you can see below there is no a lot of space before you get to the landing gear block. Based on the drawings on your website the long 90 (120) pipe is ~10" long end to end



Maybe the Turbo-Jett will work. It looks like the 10cc version might fit. I will make a balsa mock up and see if it will fit most of the way into the cowl.




_____________________________

Adrian Martinez

(in reply to bob27s)
       Post #: 3

RE: Jett Stream Muffler for Magnum .91 - 9/13/2004 8:17:20 PM   
bob27s



Posts: 4833
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: online 		Nice plane. Thanks for the follow up and pictures.

Yeah, I see what you mean on the landing gear.

That looks like an ST90 in there (photos) ...correct?

From the front view, it looks like if you mount the engine at 90 deg (looks like its at 110 now with the muffler under center), the 10cc turbo should fit entirely within that cowl. It is 3" in diameter, and about 2" tall (measure for 3.5" x 2.2" just to make sure).

Bob


_____________________________

Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host

(in reply to AdrianM)
       Post #: 4

RE: Jett Stream Muffler for Magnum .91 - 9/13/2004 9:42:19 PM   
AdrianM


 

Posts: 702
Joined: 10/8/2002
From: Palm Harbor, FL, USA
Status: offline 		The red plane is the prototype with an OS91FX. The white nose plane belongs to an RCU member from Chile. It has an ST G-90. I will do some eye-balling tonigh.


_____________________________

Adrian Martinez

(in reply to bob27s)
       Post #: 5

RE: Jett Stream Muffler for Magnum .91 - 9/13/2004 9:50:14 PM   
bob27s



Posts: 4833
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: online 		Actually........ looking at the pictures.....

it will probably fit fine with the engine mounted as is. If you dont mind the exhaust exiting off to the side a bit.

Bob


_____________________________

Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host

(in reply to AdrianM)
       Post #: 6

RE: Jett Stream Muffler for Magnum .91 - 9/14/2004 4:11:34 AM   
AdrianM


 

Posts: 702
Joined: 10/8/2002
From: Palm Harbor, FL, USA
Status: offline 		I wont fit. I just make a balsa replica and I would need a big cut out similar to the cylinder head cut out on the opposite side of the cowl.

Just how long are the 2 90 size Jet Streams from the center of the cylinder to the exhaust outlet along the mufflers axis?


_____________________________

Adrian Martinez

(in reply to bob27s)
       Post #: 7

RE: Jett Stream Muffler for Magnum .91 - 9/14/2004 1:34:19 PM   
bob27s



Posts: 4833
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: online 		The regular length 90 muffler is 8.5" long from Cylinder CL to the tip of the muffler. Barrel is 7" long.
The 90T muffler is 1.5" longer.

http://www.jettengineering.com/tech/dimensions.html

One thing of note is the muffler angle. Im not sure if that will play out in your favor.
And, if not, Dub can make a small adapter to increase the exhaust angle. We have sold these for use on the GP Little Toni

Take a look at the Toni thread here on the Jett support forum. There are pictures of the muffler installation including extensions and the muffler angle.


_____________________________

Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host

(in reply to AdrianM)
       Post #: 8

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