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partisan 12-02-2012 07:11 PM

Cutting Pitts mufflers
 
I have a Pitts muffler for my dle 20cc that I am putting on a gp extra 300. To get the cowl over the muffler easier, can I cut some length off the outlet tubes of the muffler. I can cut about 1 1/8 inches off and still be outside of the cowl a 1/4 inch. Will the reduction in length hurt the performance of the engine? My only other option is to really butcher up the cowl to get it around the outlet tubes.

-James

Gray Beard 12-02-2012 07:19 PM

RE: Cutting Pitts mufflers
 
No problem. They are made long to begin with and usually do require cutting. Won't bother the gasser at all or anything you will notice.

partisan 12-02-2012 07:36 PM

RE: Cutting Pitts mufflers
 
Thanks for the fast reply. Do you have any tips on cutting them?

da Rock 12-03-2012 12:19 AM

RE: Cutting Pitts mufflers
 
1 Attachment(s)
If you're worried about the loss of length, put it back on after the cowling is in place. ;) OK, you really don't put the metal back.

There are exhaust extensions available at good LHSs. They're nothing more than silicone tubing in a size that fits over most exhaust pipes. The main reason I use the stuff is to eject the exhaust at a point far enough from the fuselage the plane lands clean. How far is that? Usually about the same length I had to cut the pipes to get the cowl on.

I used to play with the length to see if tuning did anything for power or sound. Near as I can tell, the value is keeping the exhaust off the plane. We've had discussions about whether or not the soft tubing quietens or softens the exhaust sound, but nobody agrees.

There are two things for sale at the best LHS around here. There are the 2-in-a-pack exhaust slip-ons. They come in colors and a couple of diameters. They've got an angle in them and fancy grooves to hold zip-ties in place. They're expensive for what they are, but isn't everything. They're available and work great. Cut to kink off if you don't need it, and they work exactly like they do with the kink. The other thing is straight tubing sold as muffler coupling. It's translucent blue and has considerably thicker walls. It's sold in 8" or 10" lengths. It doesn't need ties to hold it on one brand of mufflers and is too big for the other.

For the last 5 years, I've been using hose I found at a hobby brewing supply outlet on the internet. I bought a length of the stuff and still have some left. Been giving it away to flying buddies who griped about glow fuel residue. A couple of inches extra exhaust length and they got nothing to gripe about. It's sorta thin walled but works great. Does need to be zip tied to be completely sure to stay on.

I cut pipes with a hacksaw. Have used a jewelers saw, but both require the cut be deburred. You can do that with a knife or file, no advantage to either.

nmav8r 12-03-2012 11:42 AM

RE: Cutting Pitts mufflers
 
I've been trying to find the translucent blue tubing. I had some years ago but used it. I've tried hobby shops and mail oeder and can't find it any where if you know a source post it sure would appreiciate it.

RC_Fanatic 12-03-2012 12:45 PM

RE: Cutting Pitts mufflers
 
I don't think the silicone tubing will take the heat from a gas engine (dle 20)

Gray Beard 12-03-2012 12:54 PM

RE: Cutting Pitts mufflers
 

Quote:

ORIGINAL: partisan

Thanks for the fast reply. Do you have any tips on cutting them?
I just use a cut off wheel on my moto tool to cut them. I cut at an angle so they are about level with the fuse.
NM, what tubing are you looking for? Fuel line?
You can just buy the exhaust deflectors and use that over the pipes if you like. They come in different sizes and are stocked in most hobby shops. You can just slip them over the pipes as is or cut off the ends and use them. I think Central Hobbies sells the silicone for headers.

da Rock 12-03-2012 01:42 PM

RE: Cutting Pitts mufflers
 
Quote:

ORIGINAL: Gray Beard

I think Central Hobbies sells the silicone for headers.

Central used to sell the blue silicone tubing some while back.

The silicone tubing they sell for headers is short and not very thick walled. It's really not close to long enough to use as extensions. It appears to be the same stuff I get from the hobby brewing company. Looks to be the same wall thickness if it's the same diameter. It's about two diameters in length, maybe 3. It really isn't long enough to do much of anything beyond connecting two exhaust tubes closely together. It's really not much length and is priced about $3 for what looks like maybe two 2" pieces.

It really looks like they're selling the brewing hose for connecting gas exhaust pipes together. If that specification silicone can work close to the engine outlet as it appears, it ought to be able to stand the temps at the outlet at the end of the system. But theorizing ain't half as good as testing, so tomorrow I'll get one of the guys to stick some of my stuff on the pipes out of their gassers. edit... I just ordered some and it's advertised to withstand 500F.

BTW, the blue stuff was THICK WALLED for sure. It was sold as connectors like Central advertises.

jetmech05 12-03-2012 03:17 PM

RE: Cutting Pitts mufflers
 
I had this kinda of problem,,,Except I wanted the exhaust longer...went to a good well stocked hobby shop told them the inside of the tube diameter I was looking for....and he walked right over to the boat section handed me an orange tube used on boat exhaust...worked like a champ

da Rock 12-03-2012 04:27 PM

RE: Cutting Pitts mufflers
 

Quote:

ORIGINAL: jetmech05

I had this kinda of problem,,,Except I wanted the exhaust longer...went to a good well stocked hobby shop told them the inside of the tube diameter I was looking for....and he walked right over to the boat section handed me an orange tube used on boat exhaust...worked like a champ
Any idea what the brand of that was, and what it was called? Was it metal?

Gray Beard 12-03-2012 05:55 PM

RE: Cutting Pitts mufflers
 
We used to use just auto neoprene gas line on mufflers, it would get brittle after a time and need replacement. I once used it directly on a header, I would get a couple months out of it before I had to replace it. Just using the exhaust deflectors works very well on the pipes on a pitts muffler. They already have the angle bent into them.

karasr 12-03-2012 07:28 PM

RE: Cutting Pitts mufflers
 
Mc Master-Carr
http://www.mcmaster.com/#standard-pl...tubing/=kftyfq

this is the<h3 class="PrsnttnNm"><span class="Wrd">Fuel-Resistant</span> Blue Fluorosilicone Rubber Tubing</h3>They also have pure teflon tubing.
Bob K

da Rock 12-04-2012 04:17 AM

RE: Cutting Pitts mufflers
 

Quote:

ORIGINAL: karasr

Mc Master-Carr
http://www.mcmaster.com/#standard-pl...tubing/=kftyfq

this is the<h3 class=''PrsnttnNm''><span class=''Wrd''>Fuel-Resistant</span> Blue Fluorosilicone Rubber Tubing</h3>They also have pure teflon tubing.
Bob K


Good source, thanks.

To add more info.....
They list the blue tubing as heat resistant up to 450F. I just checked the mufflers I've got on my planes and the pipes on mufflers I have are either 3/8" or 1/2" outer diameter.

The McMaster tubing sells for:
3/8" ID is $9.53/foot
1/2" ID is $20.47/foot

The hobby brewing stuff is around $2/foot but is more flexible and thinner walled. It's heat resistance is up to 500F.

My mufflers are Bisson and Slimline with 3/8" OD and Slimline with 1/2" OD. That flex stuff fits the Bisson, stretches to fit the Slimlines on the OS90s.


da Rock 12-04-2012 04:22 AM

RE: Cutting Pitts mufflers
 
Who says these forums aren't useful.... ;)

This one has benefitted me greatly, just now. When I ran down to the shop to measure those pipes (post just above), the only big-pipe muffler I could easily get to was on my OS90 powered Spitfire. It's one of Slimline's new wrap-around mufflers. As I was measuring the pipes I noticed it was just starting to get loose.

So this thread has resulted in my discovering a minor repair I need to do before I fly that plane again. See.... these forums are quite useful. :eek:

jetmech05 12-04-2012 04:37 AM

RE: Cutting Pitts mufflers
 
No I don't remember what it was it has been a couple of years now....It is used on boat exhaust .....The McMaster and Carr stuff dosen't look like it could stand up to heat


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