SJ90L muffler extension ?

SJ90L muffler extension ?
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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Engine Manufacturers Direct Support Forum >> Jett Engineering Support >> SJ90L muffler extension ?

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SJ90L muffler extension ? - 3/22/2006 12:32:36 AM

Fxrs_tim

Posts: 278
Joined: 4/4/2005
From: Austin, TX, USA
Status: offline

Bob,

I'm finally getting back to work on the Curare and have discovered that I'm going to need a 1" extension on the muffler header (SJ90L) to clear the side/bottom of the fuse. I can't find the extensions on Dub's site - can you direct me?

Also, once the extension is on, will that affect performance much? If so, what prop combo do you recommend? I'll be running Powermaster 15%, plane should weigh ~8.5lbs.

Thanks!

Tim

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RE: SJ90L muffler extension ? - 3/22/2006 2:53:56 PM

bob27s

Posts: 4637
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: offline

quote:

ORIGINAL: Fxrs_tim

Bob,

I'm finally getting back to work on the Curare and have discovered that I'm going to need a 1" extension on the muffler header (SJ90L) to clear the side/bottom of the fuse. I can't find the extensions on Dub's site - can you direct me?

Also, once the extension is on, will that affect performance much? If so, what prop combo do you recommend? I'll be running Powermaster 15%, plane should weigh ~8.5lbs.

Thanks!

Tim

Hi Tim....

Dub does not have a 1" extension listed on the web site. He does not make one like that. Extensions are available in 1/4" incriments.

You would not want to use a 1" extension on a standard Jett 90L setup with the jett-stream muffler if you can at all avoid it. It will really mess up the performance, expecially if you are looking for speed.

Of note, are you sure the muffler hits ? On my old Curares (one glass from hobby barn, the other wood from MK) I ran Webra 61 and OS 61FSR engines - with the stock mufflers, and both of those engines/mufflers fit without issue. The jett muffler should fit as well, unless the issue is clearing the wing ?

A few ways to get around this issue... kinda depends on what point you are at in the construction.

1) Do not side mount the engine 90 deg (horizontal cylinder). Mount it more at 75-80 deg with the cylinder slightly up. That will allow the muffler to clear the fuselage. (see blue king kobra photo and patriot/jett photo)

2) I do not recall if you are building this as a tail dragger or with the standard tricycle gear. If it is being built as a tail dragger, mount the engine at appx 135 deg - cylinder down a bit from horizontal. Align the muffler down below the fuselage along the center line. Use that nose gear area, and build in a pocket/tunnel for the muffler (sort of what Dave Brown did with the Illusion)

3) Dub has a form of adapter (usually used for bolt-on type engines like the OS FSR, Rossi, MVVS) that creates about a 1/4" extension, and also causes a 1/4" offset (toward the top of the cylinder). He may be able to make a Jett-to-Jett version of this. That might get the clearance you need. (see Patriot/Rossi 53 redhead photo)

4) You would want to consider the "little toni" exhaust extension package. Chances are this is long enough. This is a set of extensions about 3/4" long, with an additional kick-angle added. With the stock muffler, you lose about 1000 rpm, but you can go up 1" or 2" in pitch. 11x9 and 12x8 work well. The LX muffler also availble for this set up will get you about 500 of those rpm back. (see Toni photos)

Take a look at these images. Might give you an idea of what I listed.

Bob

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Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host

(in reply to Fxrs_tim)

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RE: SJ90L muffler extension ? - 3/23/2006 12:05:42 AM

Fxrs_tim

Posts: 278
Joined: 4/4/2005
From: Austin, TX, USA
Status: offline

Thanks for the reply, Bob. I've got the MK kit, tri-gear, with the engine mounted to the hardwood rails at a 90 degree angle. I've already got the fuse pretty much built, so turning the engine isn't an option at this point. The interference is along the bottom righthand edge of the fuse. If I can get an extension that comes out of the port and angles upward toward the top of the cylinder I'll probably be ok. The first Toni pic (w/out the cowl) looks like something that would work, if I could flip the extension over so that it angles toward the top of the cylinder. Whaddya think?

If necessary I can take some pics Friday when I get back home and send them.

Tim

(in reply to bob27s)

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RE: SJ90L muffler extension ? - 3/23/2006 3:04:33 PM

bob27s

Posts: 4637
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: offline

I understand..... I forgot about the wood rails on the MK kit.

Dub can probbly make you a 1/4" extension with one surface angled a few degrees. It can help kick-out the whole muffler away from the fuselage. That would probably allow it to clear enough.

(in the same way the toni extension is angled with the tail of the muffler a bit further way)

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Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host

(in reply to Fxrs_tim)

Post #: 4

RE: SJ90L muffler extension ? - 3/24/2006 9:07:50 PM

Fxrs_tim

Posts: 278
Joined: 4/4/2005
From: Austin, TX, USA
Status: offline

Thanks! I'll give Dub a call and see what we can come up with after I take a few measurements. I appreciate the help!

Tim

(in reply to bob27s)

Post #: 5

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