Do most QSBs have mufflers?

[Robert Vetrano]

Twin QSB 5.9s. Meridian 391. Underwater exhaust. Do most boats come with mufflers? Is it a cost thing as to why Meridians didn’t come with them from the factory? My boat is a little loud. I added Centek mufflers to my idle bypass line, thinking that was where most of the noise was, and they didn’t do a whole lot. (3″ in/out, 6″x11″).

I have about a 6′ run of 6″ exhaust hose from the mixer with room to add an inline muffler. Centek says I can add an inline muffler to the 6″ hose, and be good on backpressure using both mufflers together. Or, I may just pull the muffler in the bypass line, and rely solely on the big inline muffler.

Called Soundown and they said they’d replace the muffler I currently have with one of their own….at about 3x the cost of course.

These motors sure do sound great, but a reduction would be welcomed. My buddy just bought a Midnight Lace 52 with 6BTAs, mufflers, and overwater exhaust, and it was really quiet.

Thanks!!

Topic

[Robert Vetrano]

Thoughts on this, Tony?

[Robert Vetrano]

Got to run the boat today a bit. Due to tropical storm residual high water I was unable to get out of our no-wake zone creek and run WOT. So at the dock I started the motors first, then plugged one of the ports. I was not expecting the massive bubbling from underneath that then occurred, lol. It did, however, really quiet the noise down.

I then ran in the creek at about 1000-1200 rpm, which I usually hear an annoying drone from the exhaust while standing in the cockpit. The sound was muffled when I plugged the holes, but I also felt the rumbling from the exhaust now going mostly underwater…..so I’m not really sure what to think of that. I did still hear exhaust coming from behind the boat.

Then one of my plugs fell out and I was unable to retrieve as it went under someones dock with the wind…..so we called it a day.

Not very conclusive evidence.

[Tony Athens]

For testing, you can run at any speed or RPM.. In 99% of the cases, the by-pass is only needed to the start-up.. But with that said it all comes down to how / who designed the system

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Robert Vetrano

[Robert Vetrano]

Thanks Tony, I will try a bit harder to get that plugged. So I can do that at idle/slow speeds before I get on plane?

[Tony Athens]

I am 100% positive I can make it quite, but for now, ONLY YOU can do what is needed NOW to figure out where the issue is–The bypass, or the main underwater run……………………Spend some effort to Plug the bypass 100% and go for a good run.. Plugged 100% will hurt nothing..

Report back..

Tony

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Robert Vetrano

[Robert Vetrano]

J Dragon wrote:

Soundown designed my muffler and supported me the entire step of the way — highly recommend. And the exhaust is super quiet now.

Do you have any pictures or details on what Soundown built you? Talked again to them at the boat show and they claim they can make a much better muffler for my bypass tube than the Centek I have in there.

I’m still between putting a long Centek in my 6” hose, or spending the $ for the Soundown bypass replacements. Soundown inlines for the 6” hose are kinda out of the question…….gonna cost over $6k.

Thoughts anyone?

[Robert Vetrano]

Thanks, good to hear. Do you have a picture or details on what they built you?

[J Dragon]

Soundown designed my muffler and supported me the entire step of the way — highly recommend. And the exhaust is super quiet now.

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Robert Vetrano

[Robert Vetrano]

The guy at Soundown recommended replacing my bypass muffler with one of his. I’m not totally convinced though that all the noise is coming from the bypass. He told me to plug the bypass while on plane to narrow that down as the source of the noise. I tried to do that with a piece of pool noodle, but there’s a stream of water going right over that bypass port while on plane and I could barely get my hand over it, let alone shove something in there.

[J Dragon]

Soundown is more $$ than Centek, it’s true…but they are also a lot quieter.

Your call.

But either way, there is no doubt a muffler will help.

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Robert Vetrano

[Robert Vetrano]

Here’s some pics. Lots of room for an in-line muffler

[Robert Vetrano]

Thanks. It is not a lift muffler in the bypass. I actually have access to a suitable Centek muffler locally for $50. I kind of want to throw that in the line and test it before I spend the $800-ish for a new Centek. The guy only has 1 for sale….so its perfect for a test. The crummy part is cutting into the exhaust hose, and then having to spend a few hundred on a new 6ft run of hose if the muffler doesn’t satisfy. I’ll get some pics up.

[Justin Riege]

QSB Mufflers

I’m not sure what percentage of vessels with QSB’s have mufflers, but in general, a lot of Cummins powered boats do, and a lot don’t. Tony’s Boat with a QSB 6.7 does not. But I know others that do.

It’s not a lift muffler on the bypass line is it? I don’t think that would be ideal.

I would pop a centek muffler on the 6″ hose and give it a shot. Good chance it will help. Not a huge risk or expense to try it out.

Hard to predict exactly how it will change the sound. Sometimes one little tweak can make a big difference. Acoustics are complicated to predict. You either have to have degrees in acoustics and mechanical engineering, or you need to be Tony with 30+ years of experience seeing every exhaust configuration available.

If you post lots of good pics of the exhaust, the outlets, the bypass, etc. Tony might have some magic bullet.

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Robert Vetrano

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