Anyone have any experience designing/building exhaust "silencers"?

[Woodyedmiston]

Try to find an old copy of The Scientific design of Intake and Exhaust Systems.   Technical, about open exhausts and explains how odd stuff like motorcycle "fish tale" tips were developed, exhaust pulses and sound deadening. When the SCCA had problems at the old Golden State Raceway we did a lot of Dyno work to hit 103db   

We created a dyno-set that had no back pressure to use when testing our engines.  Whether you could do that for a variety of engine types....dunno.

But, I'm willing to talk about it 8-5 Texas time and explain what we did.

Woody 90three-216-three115

[rbeikmann]

For stationary systems, size is your friend, to get good noise reduction with low back pressure. Using drums is a good idea, and if you make the first drum large and empty, the engine sees it almost like discharging into open air.
I'd avoid flat surfaces as much as possible, to avoid having the shell of the enclosure itself acting like a speaker. The ends of typical drums might pose a problem. Burying the whole thing might be a solution, but if it ever corrodes or gets plugged...
And, as jdincau said, be careful of engines that don't start easy. I've heard stories of engines filling the exhaust system fuel of air/fuel mixture, then lighting it off, and blowing man-hole covers in the system 30 feet up!

[SPARKY]

There is a reason why gas engine boats have Bilge Blower vent systems

[Blownoiler]

I used one of these for exhaust vibration control on a home generator- http://www.ebay.com.au/itm/like/150869416070?limghlpsr=true&hlpv=2&ops=true&viphx=1&hlpht=true&lpid=107&chn=ps
It did leak some fumes, so I coated it in high temp silicone which solved that problem. The mufflers from turbo diesel applications don't actually have to muffle that much noise because the turbo itself acts as a sound deadener, so expect to run 2 in series for a non turbo app. I did try running my generators exhaust through a 60 litre drum that was filled with water to the 3/4 mark, but running the exhaust gas to the bottom of the drum (in order to force the gas/noise through the water)  does create some backpressure,  and there is a lot of evaporation so water levels need to be checked often. Unburnt fuel tends to collect in the water too, which was not a problem for my diesel application, but could pose problems for a gasoline set up. If I did it again I would just run more automobile mufflers, and would probably incorporate a large blow off valve or two for the occasional explosion.