muffler mod thoughts

cmulder Fri Mar 31, 2023 7:23 pm

Got the current production 0.049 mufflers with the small hole.
I was wondering if people already mounted a Pressure Nipple on these and then use fuel tubing to guide the exhoust away from the model.
How much power would this robb from the engine? And would this reduce the sound even more?

thoughts?

sosam117 Fri Mar 31, 2023 8:05 pm

I have modified the Cox muffler with the little hole with a thick wall K&S brass tubing.

I used a 1/4" od brass tubing and thread the outside of it 1/4-28 (fine thread) and I also tapped the original "small" hole
the same size.

Then, I retaped a nut the same 1/4-28 thd. and I used a touch of JB Weld on the nut
You could probably just use JB Weld instead and not worry about using a nut?

The tubing is long enough to get most of the exhaust oil away from the airplane. About 2" long.

balogh Sat Apr 01, 2023 12:15 am

The point is the black annulus ring on the top of these mufflers cannot seal perfectly along its edge, and especially if the backpressure inside the muffler is increased by the added choking of a long small diameter extension tube, more castor will leave the muffler uncontrolled along the circumference of this ring.. You may try to wrap the edge of the ring in the teflon tape plumbers use to seal threads, but cannot completely stop castor oozing at the edge.

And yes, the extension tube increases the backpressure of spent gases in the muffler, and robs the power of SPI engines even more than stock mufflers.

sosam117 Sat Apr 01, 2023 7:42 am

balogh wrote:The point is the black annulus ring on the top of these mufflers cannot seal perfectly along its edge, and especially if the backpressure inside the muffler is increased by the added choking of a long small diameter extension tube, more castor will leave the muffler uncontrolled along the circumference of this ring.. You may try to wrap the edge of the ring in the teflon tape plumbers use to seal threads, but cannot completely stop castor oozing at the edge.

And yes, the extension tube increases the backpressure of spent gases in the muffler, and robs the power of SPI engines even more than stock mufflers.

Well you could always modify a Enya .049 muffler to fit to your Cox .049 engine.
These mufflers seal well and the back pressure is way less than the Cox mufflers.
As for Cox engines with SPI, I would not use a muffler on them because it "needs" clean air for it to work.

As for the modified Cox muffler with the brass tube.
The inside diameter is just a little bit larger than the "old" stock Cox muffler that had the aerodynamic extension on it.

And the brass tubing "extension" is much less restrictive than the Cox car muffler.

cmulder Sun Apr 02, 2023 6:46 am

So the first try i installed a "m3" size fitting. if this is too restrictive then i also have the "m4" size.
Even the "m3" has a much bigger diameter then the original hole so should be less restrictive then original without aditional tubing

lets see what happens

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