I have a WM Midget Mustang W/ a YS 91.
Can anyone tell me what works best - Tuned pipe or Muffler?
Any suggestions on prop size?

Is it a AC or FZ?

Assuming speed is your objective, try starting with APC 13X10. I have a WM Dago Red with a fairly new YS110 with stock muffler. Have an APC 13X11 on it, giving me about 10,000 rpm on full throttle, with good horizontal speed and very good vertical.

Hope this helps

well the tuned pipe will give you more power but the 110 is already enough to pull that plane around with authority and them some!

can you post a picture of the plane with engine installed? always wanted the WM MM but couldn't figure out how to get a clean engine install in the narrow cowl!

Thanks for the info!

I'll try to post some pics soon.

Here's a few pics of my WM Midget Mustang.

The YS91 has gobs of power. I would see no need for a pipe.

I ran a YS91AC turning a 15x7 Bollie prop and pulled a CG Ultimate (9.5LBS) with tons of authority. A 15x7 Bollie prop with turn around 9700 rpm on that engine which is right where it should be.

If you want more power run 30% Cool Power Heli fuel (has 22% low viscosity synthentic oil) or at a minimum of 20/20. The oil should be all low viscosity synthentic. The more nitro the better for YS engines, they love it. Castor oil can plug the fuel injector over time. Wildcat and Powermaster make a special YS blend called YS 20/20 and I prefer the Wildcat myself. I keep a bottle of the Cool Power 30% on hand for those times I am looking to have more power for the 3D stuff with the Ultimate.

Check out the Ys Eningine support thread, tons of great info on these engines.

http://www.rcuniverse.com/forum/YS_E...mid_197/tt.htm

My Ultimate with a new YS110 (replacement for the YS91AC that it had and YS no longer makes)

If you have no sound problem at your field, use a straight pipe. You can get them at YS. Dennis

That's a great point, DadsToysBG - the fact the Y.S. is pumped means that you don't even have to run any muffler because the tank pressure isn't dependent on it. You can run it with only the header if you want!!!


Jmoga - that is a nice install... I guess 4 stroke inverted is the only way to go for the WM MM!

Four strokes will not benifit significantly power wise from exhaust systems. While technically an exhaust can be tuned for a 4S to help scavange exhaust, the power boost is nothing like what is seen with 2S tuned pipes. So, basically any exhaust systems on the YS91 will reduce power becasue it will add restriction. Pipes are used on 4S engines mainly to reduce noise, not to boost power like a 2S. For this reason, most 4S pipes are designed for pattern competition where there are sound restrictions. Of course, there is nothing stopping anyone from using these quiet pipe setups on a sport plane. A Typical RPM drop from a 4S pipe would be a 100-300 RPM drop depending upon the system. This is noticable, but not critical on most planes. As mentioned in previous posts, most power and cheapest system would be straight pipe, or even just the header. This is loud compared to no muffler, but not obnoxious IMO. I have run just headers on sport planes using YS 4S's before. If you can't run a straight pipe, just use the stock muffler. It will reduce the sound by quite a bit at minimal power loss. If you want a really quiet setup, get a 90 sized 4S pipe.

The First question is what are you trying to accomplish?? If you want all out speed then run a YS straight pipe with an APC 12x12N prop. You can run it on anything from YS 20/20 to 50/20 fuels. I race 4 planes with everything from YS 63's to 120's. The best performance I have found for the exhaust is to just put on the header pipe and throw the muffle back in the box. If the stock header is too short to reach out of the cowl then get the YS straight pipe(its not really straight). If you want lots of vertical then you will have to go to large diameter props with less pitch and a good 20/20 fuel. What ever fuel you run make sure it has ONLY full synthetic oils in it. Regular oils will attack some of the internal parts and you will end up doing regular overhauls.[8D]

get that wickid engine outa that plane and trow it in an Adenaline

www.ytinternational.co.uk

My engine can beat up your engine. (Kidding)