Casey- the exhaust is too hot for water cooling. The induced draft effect provides an adequate airflow for radiator cooling but NOT nearly enough to chill an exhaust pipe to 100F !
Regarding Glort's mention of intake noise:
Intake noise reportedly varies greatly between Listeroid engines- valve cam timing variability being the likely culpret, as in Rajkot, cam lobe placement is somewhat arbitrary, along with many other machining operations such as idler gear placement.
My own Metro 6/1 with 2001 marked parts does NOT have intake "bark". I think Dave (XYZer) reported that one of his two 6/1's does have intake "bark", and one does not. The Solderberg (sp?) air compressor intake filter is reported to be extremely effective for "barkers", as it was designed specifically for this issue in air compressors. Maybe someone with one can chime in with a model number for the unit that fits the 6/1 intake perfectly.
Checking and adjusting the intake timing lobe position seems the best solution, but my understanding was that true Lister CS engines very rarely have this problem.
I have a Listeroid 6/1 BECAUSE of the pleasant and low level of engine sound. I had to add a no load sensor (auto shutdown after 10 minutes) to my 6/1 homebrew controller because I can't hear it at my distant house site to remember that it's on. My biggest sound is the valve train clatter. Ronmar has reported using some additional soft springs between the rocker arm and pushrod end to hold the valve tappets to the cam to eliminate this clacking sound. If I had my 6/1 shipboard in close quarters, I'd use Ronmar's method to reduce that clack. My engine also has some diesel knock when it's time to clean carbon from the head, especially when it's cold.
My other tip on sound reduction is to use the urethane foam in a can to make rows of small stripes on the inside of any sheet metal area that is resonating. It deadens the sound marvelously. Instead of "boing" you get "thunk" when tapping it. Cheap and very effective for sheet metal sound problems, much cheaper and less messy than spraying foam (which also works very well). I did not need to use foam for my induced draft setup; it did not increase exhaust noise much.
About mufflers and induced draft:
For induced draft on a low speed single cylinder engine, the expansion muffler may also help to lengthen the pressure pulses, and thus improve the draft. I still get some pulsing of air flow on my setup so this a consideration. I don't know how no or little muffler expansion will affect the induced draft, as I did not experiment with it.
I love the Rumely induced draft/thermosiphon radiator cooling approach for my Listeroid; I would integrate it into my engine room like Pedro's design (to aid engine room ventilation, instead of one of my existing roof wind turbines) if I was starting over with a clean new design. I'm very pleased, Pedro, that you also see the beauty of this older farm tractor technology for your application. I also think your boat project is the most awesome application for the CS engine I've ever read about!
PS- Pedro, don't forget about your coolant expansion tank, which needs to be (just) above the high point of the radiator. I'd want a coolant level sight tube, perhaps brought to an easily disconnected ?? plate in your above deck housing. Small diameter silicone fuel tubing used for RC airplanes comes to mind. Two quart capacity for the expansion tank is sufficient, it could be hand made to fit with soldered brass sheet if need be due to your tight design space.
PPS- Alternately, to avoid complicating your vent housing removal, you could perhaps inset a small polycarbonate window in the vent housing, large enough to let some light in and see the coolant tank or level sight tube. If you are going to have to lift the vent housing daily for oiling, then this is not necessary. In your most current design, it might be possible to add a side access door to provide both oiling access and coolant level check, thus eliminating the need to lift the vent housing.
Best Wishes,
Bruce