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David Stott
Member
Username: david_stott
Post Number: 25
Registered: 06-2005
| | Posted on Sunday, May 25, 2008 - 08:34 pm: | 
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I have recently converted my Stuart Turner P55, from dry to wet exhaust, using 40 mm rubber hose and a water lift muffler. On the first test this weekend, I find I no longer can get maximum rev's the same as before and the engine seems sluggish, although runs smoothly and starts easily. Is this all about back pressure with the exhaust gases trying to push the water up the outlet of the muffler? Should I try to divert some gases around the muffler? Could I mount a lower outlet from the muffler so ther water does not have to be lifted so far? Any suggestions? |
Matthew Balkwell
Advanced Member
Username: matt
Post Number: 49
Registered: 04-2006
| | Posted on Monday, May 26, 2008 - 06:07 am: |
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David, i have attached some pics of our wet exhaust set up, recently we ran our spare engine on its trolley with the exhaust and water exiting the hose about four feet away from the engine.
This engine and the one in our boat rev and behave virtually the same[except for the knocking noise, see previous postings].
Does the water exit the boat in a pulse or in a constant stream?. Our muffler was the smallest i could buy, 150mm high by 150mm diameter.
Matt.   |
David Stott
Member
Username: david_stott
Post Number: 26
Registered: 06-2005
| | Posted on Monday, May 26, 2008 - 08:06 pm: |
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Matt,
The water exist in a pulse at lower revs, but underway seems to be constant.
I have the muffler box up in the stern with the hose going under the floor first so there is a fair lift into it. Then the water still has to be blown up and out of the muffler.
On your boat, the water has to be lifted a far greater height from the muffler to the exit than on my boat.
I might have to bypass the muffler temproraily to see what difference that makes, then I would know the pressure in the muffler is the issue. |
Roy Jones
Member
Username: royjones
Post Number: 13
Registered: 10-2006
| | Posted on Monday, May 26, 2008 - 10:23 pm: |
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Hi David,
I had a similar experience with my P66 with the wet exhaust, very sluggish, no power etc. I fitted a three way x 15mm valve in the water line after the engine salt water heat exchanger but before the muffler. By adjusting the valve so that 90 percent water vented through a separate skin fitting above waterline and the rest out via the exhaust. Once tuned I removed the handle of the valve. This now works very well indeed with the exhaust just steaming and a full flow from the water skin fitting. Cheers Roy |
David Stott
Member
Username: david_stott
Post Number: 27
Registered: 06-2005
| | Posted on Tuesday, May 27, 2008 - 06:01 am: |
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Roy, thanks for that it sounds like an idea. How did the 10% remaining in the exhaust do in cooling the hose? I suppose by keeping the amount of water in the muffler to a minimum, less pressure is required to expel it, and much may well go up as steam anyway. |
Roy Jones
Member
Username: royjones
Post Number: 14
Registered: 10-2006
| | Posted on Tuesday, May 27, 2008 - 11:51 am: |
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Hi David,
The majority of the water was just expelled as a spray and it doesn't seem to be any problem. It certainly keeps the exhaust system cool enough to hold ones hand on the pipe. One thing I didn't explain was that I have a raw water pump (ie salt water) that is belt driven off the flywheel and this water is pumped through the heat exchanger (to cool the fresh water inside the engine) before being pumped back over the side 10/90%. I agree that when I first installed the wet exhaust, at an idle it was fine but only when you want power does the back pressure cause trouble. Caused plug fouling too. Cheers Roy |
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