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MVVS 26IFS on a Twin

Old 02-21-2007, 05:59 PM
  #1  
gsmith6879
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Default MVVS 26IFS on a Twin

I thought the MVVS experts would like to see what an average modeler could do to a pair of perfectly good 26cc gassers. This is the final installation of the engines I bought from PE on my 1/5 scale OV10 Bronco. This is my test system to allow me to fine tune the setup before assembling the rest of the airplane. They run great and the silencers do the job without restricting the engine. The concrete block on the bottom of the test stand atests to the brute power these engines are producing.

If you see anything in the photos that looks wrong, please let me know before first flight.

Thanks for the help on this forum.

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Old 02-21-2007, 06:32 PM
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Default RE: MVVS 26IFS on a Twin

Great show Gaines,
These exhaust systems must have been a plumber's nightmare. You got them tucked away nicely.
Video of engines running by any chance?
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Old 02-21-2007, 06:52 PM
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Default RE: MVVS 26IFS on a Twin

Yes, a plumbers nightmare. They are a bit louder than the stock silencer that I used to break in the engines but OK for the wide open spaces of Oklahoma.

I have some linkage changes to make and will get some video of the engines running in the morning.
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Old 02-22-2007, 09:07 AM
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Default RE: MVVS 26IFS on a Twin

With the long headers, you probably can reduce the stinger diameter quite a lot before power loss sets in. That would reduce the sharp exhaust note considerably.
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Old 02-22-2007, 01:11 PM
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Default RE: MVVS 26IFS on a Twin

Good point. I have 22mm/7/8" coming out of the engine to the silencer and 20mm/3/4" from the silencer out the side. That 22mm/3/4" tube is about 170mm/6 3/4" long. What size would you recommend as starting point to experiment with?
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Old 02-22-2007, 01:37 PM
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Default RE: MVVS 26IFS on a Twin

1/2" as stinger should be a nice starting point. from there, experiment. You can connect it to the original, but now very short 3/4" stub with silicone hose.
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Old 02-22-2007, 04:29 PM
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Default RE: MVVS 26IFS on a Twin

I'll machine a piece of aluminum to fit inside the 3/4" tube. I'll start with 1/2" and see how they run and adjust accordingly. I'll bore a taper on the inlet side.

The referenced video shows the engines running. I'm using Bill Wike's TwinSync to handle the synchronization of the engines. During the individual run tests the left engine was running about 200 rpm slower that the right. The TwinSync pulls the faster engine back to match the slower engine.

Along with running 200rpms slower the left engine also is putting out a lot more oil in the exhaust than the right engine. When I try to lean it out a bit it sags (too lean). I pulled the plug and it looks about the right color so I am just going to leave it alone. Better too much lubrication that not enough. The lower rpm may have something to do with the different plumbing on the exhaust.


http://www.youtube.com/watch?v=egIKZSZNAjQ
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Old 02-22-2007, 06:01 PM
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Default RE: MVVS 26IFS on a Twin


ORIGINAL: gsmith6879

I'll machine a piece of aluminum to fit inside the 3/4" tube.
snip

http://www.youtube.com/watch?v=egIKZSZNAjQ
That is not such a good idea. A flexible join is better and will keep your muffler from harm


Along with running 200rpms slower the left engine also is putting out a lot more oil in the exhaust than the right engine
Maybe you can use the stingers to equalize both engines. Don't worry about the oil out the exhaust. Set each engine for best power, and then adjust with the mufflers.
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Old 02-22-2007, 06:17 PM
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Default RE: MVVS 26IFS on a Twin

I have flex joint between the muffler and the tail pipe. I use a teflon sleeve and clamps. The 3/4" tube is supported inside the large SS tube you see on the side of the nacelle by silicon spacers (fuel tubing siliconed to the tube). I get some airflow around the hot tail pipe.

See if this makes sense. The third photo is the 3/4" tube into which I have installed the restrictor I machined.
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Old 02-22-2007, 06:42 PM
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Default RE: MVVS 26IFS on a Twin

The tail pipe will not get very hot, at least not so hot as to cause worries. The header/muffler coupling gets much hotter. and may need special attention to keep from slipping.
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Old 02-24-2007, 10:46 PM
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Default RE: MVVS 26IFS on a Twin

The 1/2" stinger insert helps some on the noise and I had no decrease in rpms. A strange thing did happen to the left engine with the more complicated plumbing. It was running too lean with the addition of the 1/2" insert. I had to open both the high and low speed needles about a 1/4 turn. I actually picked up about 50-100 rpm with the insert. Have I stumbled on to some kind of tuned pipe effect?

Since it is very easy to machine the inserts and change them out I am going to try a 3/8" and then work back up to the 1/2" if the smaller insert hurts the power.
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Old 02-25-2007, 05:51 AM
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Default RE: MVVS 26IFS on a Twin

Your system has an extractor exhaust pipe, and needs muffler pressure to stop the outflow of gasses. Different extractor pipe length's need different pressure to stop the flow. This is typical for all two stroke engines, and your left engine was not in the same tune as the right because of that.
The improvement shows you are on the right track.
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Old 02-25-2007, 05:52 AM
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Default RE: MVVS 26IFS on a Twin

PS,
I cannot get my browser to load the U-tube video. Updated Java etc. still no go. Any idea why?
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Old 02-25-2007, 01:54 PM
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Default RE: MVVS 26IFS on a Twin


ORIGINAL: pe reivers

PS,
I cannot get my browser to load the U-tube video. Updated Java etc. still no go. Any idea why?
Pe,

I don't know what could be the problem with Youtube. Can you download videos from the Rcuniverse video site?
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