Flex pipe for a Magnum 91 4 stroke
 

I caqn't find any info on exhaust thread size for this engine. Any idea if the OS flex pipes will fit the Magnum?

RE: Flex pipe for a Magnum 91 4 stroke
 

[:@]hi
I don't know to help but i want to ask you a question!
Does this engine runs great?
Also i want to buy one,where can i found a 91 4str.?[:-]

RE: Flex pipe for a Magnum 91 4 stroke
 

stas, I have two Magnums. A 1.20 and a .91, both 4 strk.

They are excellent running engines, just not as light as some other brands.

RE: Flex pipe for a Magnum 91 4 stroke
 

The OS and Magnum exhausts are the same diameter but the thread pitch is different in the 52 size.

Enjoy,

Jim

RE: Flex pipe for a Magnum 91 4 stroke
 

Thanks jim. Any idea what I could use?

RE: Flex pipe for a Magnum 91 4 stroke
 

At Lowe's they have gas pipes that are brass and accordion looking. I saw a small one a couple weeks ago that was brazed to the original pipe on a old double rocker box OS 120. It looked nice.

Enjoy.

Jim

RE: Flex pipe for a Magnum 91 4 stroke
 

I tried a stainless natural gas pipe from a water heater on my magnum 91. It worked great as far as an extension but it whistled. Pretty funny really. Am told the coregations (spelling?) in the pipe make the whistle. I had it hooked on the end of the muffler with a hose clamp. I did notice a marked drop in performance. I ended up pulling it off and letting my smoke system dump out the side instead. I am no guru but would guess it was due to hooking it on the end of the muffler.

What do you think Jim?

Eric

RE: Flex pipe for a Magnum 91 4 stroke
 

Normally, a four stroke is not very sensitive to exhaust extensions. I don't know in your case.

A couple things come to mind.

One- The engine is quieter and seems like it has less power?

Two- The corrugations caused increased flow friction?
[hr]
But the flex extension sold by Saito are corrugated.

I don't know,

Jim

RE: Flex pipe for a Magnum 91 4 stroke
 

It was MUCH more quiet. My duster also needed a good extra 50 feet of roll to get off the ground. I also lost a lot of vertical performance. I think you may be right about the flow friction. But it was really funny as it whistled by. We all had a good chuckle and then I scrapped the idea. Now that I think about it I bet you could use a length of the stuff between the header and the muffler. I still have it int he garage. Maybe I will tinker with it this spring again.

Eric

RE: Flex pipe for a Magnum 91 4 stroke
 

I found some flexible steel electrical conduit. I need to figure out a way to flare the end to fit on the elbow. If I can't get that to work, then it is off to find some of this brass tubing you guys mentioned. Thanks for the tips, and I'll let you know what I find.

My idea is to run the flex right off the elbow, elimating the muffler. A friend of mine has a set up like that on a 120 Saito. No pressure, but it seems to run OK. If I do need pressure, then I guess it's back to the drawing board.

RE: Flex pipe for a Magnum 91 4 stroke
 

I bought a brass collar (forget the size) that was just a hair too small to fit on the muffler exit. I used my dremel to open it up a bit and then used JB weld to hold it on. This increased the diameter (outside) enough to allow a hose clamp to crimp down on the stainless pipe. To facilitate more crimp I placed the stainless pipe over a scrap of round metal rod and gently persuaded it to be a flat circumfrence with my 3lb hand maul. Then I cut a few slots with a cutting disk on my dremel. I think it was four, about 1/4 inch long. Wrapped the brass sleave with teflon plumbers tape and crimped it all together. No leaks. I am sure those out there who can silver solder or weld would have better looking results but it worked for me. Am interested to hear how it works out for you.

You could always add a regulater/pump if you have pressure problems. With a cline regulater you could also move your tank anywhere you wanted if needed as an added bonus. Have thought about this too, but was disapointed with the drop in power so did not try.

My next idea is a variation of the mousse can craziness in the two stroke world. I know it will not act like a tuned pipe does on a two stroke but I found a $1.99 can that is roughly the size of a good pitts muffler. I have a smashed pitts muffler from an OS 61 two stroke that I can liberate the down tubes from and JB weld them on my can. Oh the fun one can have for under $5. :D

Eric

RE: Flex pipe for a Magnum 91 4 stroke
 

That flexible electrical conduit leaks all over. It will be a oily mess after you run the engine.

The natural gas/propane flexible brass connectors are one piece with no seams. Its real thin and not so heavy.

Enjoy,

Jim

RE: Flex pipe for a Magnum 91 4 stroke
 

I read this a couple of days ago and something bothered me.

I thought I had used a muffler off an O.S. FS91 on my Magnum 70 RFS. Without digging the engines out of their planes, I've found that the O.S. and Magnum 91's (as well as the 70's) DO have the same thread pitch and diameter. M11x.75 . Check these sites http://www.hobbypeople.net/gallery/210970.asp and http://www2.towerhobbies.com/cgi-bin...?&I=LXCB42&P=0 and confirm this. The way I read it, the O.S. flexpipe should thread into the Magnum cylinder head. The short flexpipe is at http://www2.towerhobbies.com/cgi-bin...?&I=LXXE97&P=0 and the long one is at http://www2.towerhobbies.com/cgi-bin...?&I=LXXE98&P=0 .

Sorry about not responding sooner, I just wasn't real sure about it, but, well, it was bugging me so I had to dig!:)

Dave

P.S. I have never used one of these but, I have tried the Mac's Muffler flexible stuff and I am convinced that these will be WAY more leak free.

RE: Flex pipe for a Magnum 91 4 stroke
 

In the 52 size the thread pitch is different.

I just tried swapping mufflers between a Saito, OS and Magnum 91. The Saito is a larger diameter.

The OS and Magnum 91's fit each other perfectly.

Enjoy,

Jim

RE: Flex pipe for a Magnum 91 4 stroke
 

SWEET! Thanks guys!!!! The knowledge on these boards never ceases to amaze me.

RE: Flex pipe for a Magnum 91 4 stroke
 

I tried using some of those neat right angle adaptors and solid pipes Saito offers with the v-twin and radial engines to build a truly "in cowl" exhaust for a Modeltech SE5a/Magnum 52 combination to get rid of the big honkin' silver muffler hangin out of a perfectly nice, scale looking cowl. I got the diameters right, wrong thread pitch... :eek: I ended up brazing some aluminum pipe up to half of the original elbow, with a few bends in it. It worked longer than the plane did![X(] I Dirt napped it doing combat with a Great Planes DR1, looped it just a little too low, BUT, I did get some of his ribbon...:D And the crowd went wild..... (applause here)

It appears that Saito goes their own way on thread pitch while Magnum/ASP is copying theirs as per the O.S. blueprint.

Dave

RE: Flex pipe for a Magnum 91 4 stroke
 

Its true on the mag-os thread size, at least on my .91 mag. I used a 90 degree header pipe on my mag in my tiger moth and it fits perfectly.

Merry Christmas,
slopoke