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Volvo penta DPS B outdrive exhaust noisey

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Ivos

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Why does all the exhaust come out the cavitation plate I thought the dps B outdrive was exhaust out propeller to make them quiet or am I wrong ?
 
Volvo drives prior to the SX did not have thru the prop exhaust and as a results are noisy at cruise and above. I got tired of the noise of my 260Hp engine via my 280 drive on my 23 ft cuddy cabin so I redid the whole exhaust run from the elbows outward... I installed a pair of CENTEK 3" shorty fiberglass mufflers in line with a pair of 3" outlet ports thru the transom. The mufflers are installed parallel to the transom with a right angle elbow out to the transom. I also installed a pair of 4" to 3" "right angles" at the exhaust elbows. An unanticipated side effect was that the engine gained 450 RPM @ WOT. Its not exactly quiet at the helm, but my wife and I can carry on a conversation without shouting. At idle, has a great rumble.
 
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Mine does have exhaust through prop but alot of exhaust comes out of cavitation plate which is out of the water at planning speed ,does anyone know if I can baffle the cavitation plate or will I create to much back pressure, im willing to sacrifice some horses power for comfort ?
 
On my 280 drive, when I changed over to thru transom with dual 3" lines and dual fiberglass mufflers, I gained 450 RPM at WOT on my 260 HP 5.7L engine. My wife an I can however have a conversation at the helm when cruising.
 

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Ivos said:
Why does all the exhaust come out the cavitation plate I thought the dps B outdrive was exhaust out propeller to make them quiet or am I wrong ?
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I am currently working on the same problem. There is a fella in Australia by the name of Stuart but she have to be a Glasstron owner which I am not but he discusses putting a plate on the back of that outlet and apparently it made a massive difference in the sound. I'm in the process of doing exactly that but not completely blocking it because part of the cooling goes through that same port and I wouldn't want to overheat the engine. I'm mounting it so that it covers that hole & is braced from a arm that attaches to the sacrificial anode above it and goes over the upper lip attaching to the back of the blocking plate. thus creating a stable resistance from it being forced out.
 
You’re not wrong! I thought the same thing, as the exhaust is supposed to exit through the prop hub to help keep the noise down. But some exhaust can also come out around the cavitation plate, especially at idle or low RPM. If you’re seeing most of it coming out there even while cruising, I’d check the exhaust connections and bellows to make sure everything is working as it should.
 
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