Is there an after-market muffler (not tuned) that will actually improve the performance (output) of this engine. Anyone tried one that actually made a difference.

Performance Specialties has a very good bolt on tuned exhaust that boost the power about 1,500 prms. I have used them in the past and are better than tuned pipes.

http://www.pspec.com/ look for Ultra Thurst Mufflers

2 things that you can do that are fairly cheap that will boost your performance are 1) take the baffle out of the stock muffler or 2) buy a Tower 46 muffler.

I took the baffle out of my 46fx on my UltraStick and it added about 1000 rpm and that sucker screams along now. It's a little louder, but still quieter than my Pitts muffler on my Bipe.

Steve,

I am using the Tower Hobbies .46 muffler on my .46FX.

With an 11.5x6 prop, RPM has improved by about 600 RPM, over the de-baffled original OS 873 muffler. I am told that when using 10x6 and 10x7 props, the improvement is about 1,200 RPM over the original OS 873 muffler, with the baffle in place.

If you buy the Tower Hobbies .46 muffler, you will pay $15 and if you buy the Hobbico muffler, which is essentially the same thing, you will pay $13.

The Nelson SuperThrust is an efficient tuned silencer, but it shouldn't be any more expensive than the Tower unit.

It must be made of gold...

I have to second the idea on the Tower .46 muffler. I found out about the performance improvement by accident....I lost the back half of the OS muffler in flight. OS won't sell just the back half and they want 24.95 for a new muffler.

Tower sells the Tower .46 muffler for a lot less and it qualifies for their special 3 day shipping.

I was the most surprise person when after installing the Tower muffler my Tach showed almost 500 more RPMS with the same fuel and prop.

It is a bit louder ......but it sure pulls noticably harder. I'm not running any leaner still have visable smoke showing.

Try it you will like it.

P.S. I have 2 front halfs of the OS mufflers if someone needs them (cheap)