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bob27s -> RE: Jett stream muffler (1/10/2007 3:01:27 PM)
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Hi,
Thanks for writing....
The Jett-Stream muffler works quite well on the OS61. Yes, it is the same muffler used for the OS91FX, and is also the same muffler used on the Jett SJ-76, SJ-90L and BSE-100L
This particular muffler featuers a dual bolt pattern that accomodates the OS 61/91 spacing, as well as the Jett/Supertiger bolt spacing. So it may be used on a variety of engines. Adapters are also available for use on Rossi 61, GMS, YS and other 'bolt-on' flange muffler type engines.
There is no variation in physical muffler sizee for the 10cc to 15cc class engines. With the tuned exhaust, the target rpm is the key characteristic.
The ultra-thrust is a nearly identical design. Same concept, simply packaged a bit differently. Dub Jett and Henry Nelson originally developed these muffler designs for F-1 racing, Q-500 racing and QM40 racing. Jett extensively developed the same design concept for use with his line of Sport Jett engines and subsequently other brand engines.
With the Jett-Stream, you will find a gain in rpm similar to what you noted, depending on the prop you select. The Jett-Stream muffler is tuned for a target peak ground rpm somewhere between 12,500 and 14,500 rpm. Selecting a prop that permits the engine/jett-stream combination to hit 13,000-13,500 is ideal. You will find that this rpm is about 1000-1500+ rpm higher than the same prop when using the stock OS muffler. The engine will also unload a bit more in the air.
The OS91 and ST90 both run great with this muffler. Quite a few flying this combination in pattern ships and some prop jets using 11x9, 11x10, 12x8 props. The OS61 performs similar, but with the reduced displacement you have to run a bit less prop. I would suggest starting with a standard APC 11x7 to begin with. That will allow the engine to turn up to its best performance point. From that, and depending on your application, you can try other prop sizes for optimal performance.
I hope this is helpful....
Bob
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