I've run a Fox .35, OS .40LA, OS .46LA and a Brodak .40 using both tongue and the stock tube mufflers. In every case the engines were easier to needle and seemed more constant in speed for the entire flight with the stock  tube mufflers .

I wonder if the current tongue mufflers don't have adequate volume and the exhaust port sees a higher pressure. I think the net result would be residual exhaust gases in the cylinder and higher engine temps as a result.

Have any of you experienced the same?

I tried them both and really couldn't tell a difference except the tongue was a little louder but it was also a little lighter which also helps balance this ship. Power wise I didn't see a difference. OS40FP. Often you will find that a tongue will not perform as well as a tube muffler and its usually because of the lack of holes (exit area) in an effort to keep the noise at a respectable level. Opening the holes or adding holes will return the power but also increases the db's or noise. There is a point of diminishing return when opening the exit holes where the power will not increase anymore but the noise will. I have never done it but I have seen some use small screws to block the holes in a tongue muffler to get the run time adjusted. Blocking the holes increases the run time. Kind of the same as reducing the venturi. You can do the same thing at either end.
     It really doesn't matter if it's a tongue or a tube, if the exit opening is too small the engine will run hot and or be down on power. If done right (tuned pipe) muffler back pressure can be your friend. Crankcase pressure is forcing the fuel into the combustion chamber and the exhaust back pressure is not letting it flow out of the engine. It's the basic principle that tuned pipes work on. By having negative back pressure fuel is held in the engine longer and in a larger amount as opposed to allowing it to flow straight thru. This packing of the fuel in the motor or combustion chamber before the port (piston) closes is a benefit to increased horsepower and can be used to control the RPM where the engine makes its horsepower depending on the pipe configuration, taper or reverse taper in some cases of the cones, baffels, pipe length, exit size etc. etc.

I have had to open up a toungue to get consistant runs on a 40 FP. Its interesting to know that you had to plug some up on other engines.

Not real scientific but as a starting point I measure the outlet of the stock muffler, calc the area and make sure the area of the holes in the tongue muffler are at least as large. If larger I leave it alone, if smaller I enlarge a few holes so it's the same.

Like most things stunt, there never appears to be one answer. 

I "borrowed" this from Randy Smith's vendor section post re: Aero Tiger 36 comments.

HI Leester

  I had  stock and They are normally stock items however I sell out very fast over the holiday season, and this year had a very big demand for them, I plan on having the AT 36 back in stock soon, as I still have a few unfilled orders.
With most all motors tube mufflers are better, they flow better  sound  smoother and  are normally quieter. The reason to  use a  tongue muffler over the tube  is  strictly  weight.  many planes can''t stand more nose weight.My CNC tube  are  only about an ounce. You can judge  your situation on mufflers from that.

I will try to post some of the new products  here  soon

and  specials

Regards
Randy

So what you all are saying about adding restriction to your tongue mufflers doesn't square with Randy's opinion. Not trying to heat this up at all just looking for the most reliable engine set up. As I said, The Land of Stunt is a peculiar place!

<Not trying to heat this up at all just looking for the most reliable engine set up.>

I think a reliable setup is a reliable setup and really has nothing to do with using a tongue or a tube muffler. IMHO

Just a little side note. On my plane when I ran the tube muffler it sprayed oil all over the wing and fuse but when I ran the tongue everything was a lot cleaner. It's just how everything is setup and what direction the muffler exit is pointing, may be different on other ships. So just use what works best for you. I think....Grins

<Not trying to heat this up at all just looking for the most reliable engine set up.>

I think a reliable setup is a reliable setup and really has nothing to do with using a tongue or a tube muffler. IMHO

Just a little side note. On my plane when I ran the tube muffler it sprayed oil all over the wing and fuse but when I ran the tongue everything was a lot cleaner. It's just how everything is setup and what direction the muffler exit is pointing, may be different on other ships. So just use what works best for you. I think....Grins

Hello Dick and Greg ... All

Thanks for your input, I will add a little more to what I said, I use my tube mufflers whenever possible, I do use the differant size silicone exhaust divertors with the tube, This helps keep the oil deflected downward, so Greg that is the best way to keep the oil off your ships, however if the fuel has oil some of it will get on your plane no matter what you do.
The silicone divertors  come in 7 ,8,9,10,11 MM and a few other sizes so you can adjust your back pressure this way with a tube expansion chamber mufflers.
Keep in mind running them long will increase back pressure, cutting the short will reduce pressure.
Also what ever you do to one end of the tube will effect the other (muffler hole-venturie) So closing down the venturie size amount to much the same as closing down the exhaust hole or holes.
I have seen several people run tongue mufflers with the venturie drilled out way too big, then they install 5 or so screws to clock up the holes in the muffler, the reverse can happen too.
IT IS better if you get a balance (venturie size and muffler outlet)so you do not have to go to extemes in either direction.

Regards
Randy