ORIGINAL: ukmike
Hello.
The standard DL silencer can be easily modified to reduce the noise and with very little cost.
Just get some tube that is a tight slide fit into the existing outlet and blank off one end. Slide it into the outlet as far as it will go (blanked off end first ) then mark and cut it to the same length as the existing one also mark which part of the tube is actually inside of the cannister section.
Drill 4 x 1/4" holes evenly spaced into the new tube at a point that is inside the cannister body. You now have a restrictor that you can "tune" by adding more holes of varying sizes to acheive the desired effect. The 4 starting holes will be enough to get the engine to run. A little power loss will be inevitable.
The new restrictor is held in place by drilling a couple of holes thu' both tubes and secured with self tapping screws.
When you are happy with the "tuning" the fix can made permanent by smearing a little exhaust compound around the the restrictor tube as you finally fit it.
Good luck.
Mike.
This will severely reduce the available power. It is the system I use when I do not have much time (most of the time), and I can spare to wring in a few extra cubic inches to compensate for this less desirable approach. Whilst it is true that it reduces the noise considerable, it also reduces power very much.
(Above sentence is edited.)
Much better is to eliminate as much of the prop noise first by:
as first and most important resource, increase disk load without increasing rpm
so: Increase engine LOAD AT LOWER RPM
DO SO BY INCREASING PITCH, NOT DIAMETER. This keeps tip speeds down and away from near sonic fluid flow over the airfoil (air also is a fluid)
As second consideration, increase the number of blades. In a three bladed prop, narrower blades will perform surprisingly well! (disc coverage factor) There is a limit to increasing blades, so increasing diameter is next.