Just curious if anyone might have a muffler for a YS61SF? Macs, I see, sells a muffler(#6700) and an adapter(#6808). I thought, maybe, in someone's pile of used stuff there might be a muffler hiding that used to be on the YS61SF. It would be going to a new home and brand new in box 61SF. I don't want to use a "strap on" if I can avoid it.

I would give Jett Engineering a call, or Performance Specialties (Ultrathrust). See if they have a muffler that will work, which I am sure they will, and an adaptor. In fact, I'm thinking of doing the same thing myself. I have a YS.60 side exhaust ready to go into a Dirty Birdy.


Ed Cregger

In another thread I have mentioned my difficulties with an OS91FX(two stroke) using a pressurized fuel system. I was using a Cline Regulator taking crankcase pressure for the tank. The UltraThrust muffler made the engine almost not run. Dave at Performance Specialties told me that the muffler pressure and crankcase pressure cycles interfere so that the engine will not run correctly. I know the YS pumped engine "may" operate somewhat differently than the Cline system, but I don't feel like buying another UltraThrust/Jett Stream type muffler only to find it is also incompatible.

What happened with the muffler pressure charged fuel system using the Cline regulator cannot happen with the YS' totally isolated pressurization and regulation system. The muffler is decoupled from the fuel regulation function entirely.

What is the point in using a high performance, pipe timed engine with a conventional muffler? Makes no sense. Without a resonant exhaust, chances are the YS will not perform as well as a standard timed .61 running a muffler. To make matters worse, its regulation system was designed to run with a resonant exhaust, so you could be back in the same situation that you were before when running unmatched exhaust and regulator systems.


Ed Cregger

You have a valid point. I have a YS61(either Long or AR) with a tuned pipe on an Atlanta that just runs beautifully. The Cline system pressurizes the fuel tank via a one-way check valve in a line from the crank case. Then, the fuel to the carb flows thru the regulator much like a SCUBA tank system. I was assuming the YS crancase pump acted somewhat similarly and maybe I would have the same problem using the UltraThrust/JettStream muffler. In the particular application I am trying to remedy by replacing the OS91FX with the YS61SF, I will be unable to use a tuned pipe and must use the shorter engine mounted muffler.

Hello Airbusdrvr,
My 61SF runs beautifully on a muffler. It even idles at 1500 RPM!
On a muffler, it is a better torquer, because it is relatively low-timed for low RPM pipe use.

YS never made a "stock" muffler for this engine, but Hattori did.
It was a plain expansion chamber: not much good at making the engine quiet.
Look to the aftermarket like Jett or Performance Specialties.

best regards,
Dean Pappas

Dean Pappas has spoken. That's good enough for me. <G>


Ed Cregger

Someone help me a bit. Do I understand correctly that the Jett Stream and UltraThrust are a shorter tuned pipes? I seem to remember someone referring to them as "half pipes." A muffler is generally just that, a quieting device. Dean Pappas, are you referring in your example to a muffler or the performance muffler/pipe(JettStream/UltraThrust)?

I'm not Dean, but I think Dean is saying that the YS .61 is not set up radically enough to run poorly on a muffler. The more radical the pipe timing, the less it will benefit from *A* pipe and the better it runs on a muffler.

The YS .60 short strokes are really wasted when ran on a muffler and not the proper tuned pipe.

Myself, I wouldn't consider running any YS on anything less than an Ultrathrust or Jett muffler.

As you seem to understand, the wavelength of the pipe does have an effect upon how much benefit it bestows upon the engine. Short resonant mufflers run at 1/8th wavelength, IIRC. This means that the force of positive and negative pressure waves would be 25% that of a normal 1/2 wavelength tuned pipe.

Of course, design efficiencies then enter into the equation (always reducing - never adding, when compared to the theoretical maximum). Still some boost is better than a constant positive pressure fighting the exhaust leaving the port as is obtained with a conventional/non resonant muffler. It has been a while since I studied this material, so if I'm off on the numbers I apologize, but the principle is correct, I'm sure.

Ed Cregger


____________


Even I can't understand what I wrote in the first paragraph. Musta been a TIA. Correction with the * * above.

Ed Cregger

Hi Gang,
That's right Ed. Even the long-stroke is mis-applied with a muffler, but it runs great with a 13-7 APC sport prop!
The "half pipe" designs like the Jett and Ultrathrust should run fine.
Half pipe is a misnomer, these high performance mufflers were designed originally for the Q-40 "muffled" racing class.
The tuned length is folded, in a manner not unlike the old Phelan Magic Muffler, Rossi Q-40 muffler and others.
They work great, and I believe that their manufacturers will sell you a 90-sized muffler, or an exhaust stack extension,
for a 60 that is intended to be run at moderate RPM, in order to satisfy noise considerations.

later Friends,
Dean

The YS 61F.S. side exhaust(YS0080) just arrived. I'm asking one more time if someone might have in their used surplus "stuff" a muffler for this engine. I guess Monday I'll be calling Jett Eng or someone for a tuned pipe type muffler if not luck here. [&:][8D]

Dean,

Ricght on. I'm running my "secret" set-up in SPA with an OS 61FX and the OS91FX Ultrthrust. Tunes down really nice and turns a 13/6 APC on 15% with a LOT of vertical.

Rich Ernst
TeamVortex
FVPA
Oops, guess it's not a secret anymore....(g)

Rich, would the .91 Ultrathrust be a good match for the long stroke SF .61 for turning larger props? I'm turning an APC 12x8 at 10,740 and an APC 11x10 at 10,920 with the stock muffler now. I don't even know if those are good numbers.

Thanks,
David

I just spoke with Dave at Performance Specialties and he is very positive in his saying the UltraThrust(and JettStream) type muffler/pipes will be incompatible with the YS61. He said it would probably run wide open and at idle but nothing in between. He said back pressure would affect the diaphram pump. I'm still searching for a compatible muffler for the YS 61S Long Stroke. I really hate to have to go the Macs Pro way and pay $70 for their pipe($47.95 muffler, 10.95 adapter plus shipping). I really wish one of you guys who has a muffler lying around for the YS would send it to a good home. [8D][&:]

The YS.61 uses a regulator, not a pump...


Ed Cregger

I just ordered an OS 61FSR muffler from Mecoa. It is supposed to fit the YS. My fingers are crossed. Dave at Perf. Spec. said my OS91FX wouldn't run right with his UltraThrust and the Cline Regulator and he was right. I hate to gamble on another UltraThrust/JettStream for the YS61 when the guy that sells the muffler says it won't run right. However, if someone would send me one, I'll install and test it. I'm just trying to get this plane to run.

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No doubt, I would take Dave's word for it. I'm not questioning that at all. You did good by contacting one of the most knowledgeable folks there are about this topic.

I would like to know his reasoning on this topic, though.


Ed Cregger

Yes Ed, I spoke with Dave yesterday afternoon. He explained some pressure wave interference between the pipe and the diaphram. As I mentioned earlier, "I don't understand all I know about this subject."

And yet the engine runs just fine with a full size tuned pipe...?

Must be the muffler's higher frequency of pulses getting places where it shouldn't.


Ed Cregger

I wonder if the old Magic Muffler Types would work with the YS?

turbo

I always assumed (there's that word <G&gt that the old Magic Muffler worked similarly to the Ultrathrust and Jett non round mufflers.


Ed Cregger

I think you're right Ed. I found this article : http://findarticles.com/p/articles/m..._n8855982/pg_7

turbo