3" thru hull exhaust too loud, want to tone it down

[tfret]

First let me apologize for posting something that seems to have been kicked around a lot on various forums. But despite hours of searching I still can't find a practical or affordable solution. I have a 5.7L sterndirve Mercruiser in a 19' 1984 Dixie ski boat with 3" thru hull exhaust. It's just to dang loud! I wish it were practical to convert her to thru prop, but pulling the engine, cutting a hole in the 30+ year old transom to install a Y pipe and bellows just isn't practical. The only marine mufflers I can find are very expensive and probably too large to fit anyway. The boat has a very shallow 80's sport boat hull so clearances are tight and there's just not a lot of room to work with back there. Finally the tips and inserts I find seem to all be geared toward larger ocean going cigarette boats, not a little ski boat like mine. I can't find any inserts for a 3" thru hull flange. The only 3" inline silencers I've found are "not available". It just seems like there is no 3" market out there. I've even considered some of the automotive universal "bullet" exhaust mufflers that are made from 304 stainless. They may fit and "should" last since they are 304 stainless but I still have doubts how long they'll hold up. I'm just frustrated at the lack of options I seem to have, and definitely ready to a quieter ride. Thanks for any and all help!

 

[alldodge]

There just really isn't much out there as you've found. The SBC doesn't gain much of anything by going thru hull so finding things is just about empty. About your only options are water mufflers inside the boat, auto mufflers or turndowns.

The water mufflers will take some room and some special fabrication
The auto mufflers probably as you say won't last long (maybe a few years)
The turndowns will only quiet it around idle speed

 

[Rick Stephens]

I would do the through prop mods. Far simpler and effective than any other choice. You have to pull everything, but that is just a couple hours work. Every other choice takes custom fab work, always time consuming, frustrating and much more spendy.

 

[Scott Danforth]

get a set of 3" in-line marine mufflers. $180 a pair

http://www.cpperformance.com/p-12628...ers-3quot.aspx

 

[tfret]

Thanks for the comments. Yes, my ideal solution would be thru prop. I'm not really set up to perform such a task, and frankly I guess I'm a little bit afraid of what I might discover sawing a hole in the transom. Old boats can be a can of worms. At any rate it's an old boat and I really am hesitant to get into all that.
I did see the CP Performance inline silencers. Exact same item and part number as Harden. Best I can tell they are simply silencer inserts(that are commonly available in 4") welded into a camber that splices into the exhaust hose. They are a bit pricey. I wish I could just find the inserts alone and stick them in my flanges for half the cost. That way it's easily undone if need be. I think installing them would be pretty simple. But I hate to cut those hoses then decide to go back. I'll never find the same OE hoses. They are "Z" shaped. But that might be my only "simple" answer.

 

[alldodge]

CP, Hardin are the same items, always wonder why they have two places

 

[Bondo]

Yes, my ideal solution would be thru prop. I'm not really set up to perform such a task, and frankly I guess I'm a little bit afraid of what I might discover sawing a hole in the transom.

Ayuh,..... Is this an I/O, or inboard,..??

If an I/O, ya just take the blockin' plate off, 'n bolt the y-pipe on,.... No hole cuttin',.....

The only way to get it Quiet, is to get the exhaust tips underwater,.....

Any dairy farms 'round yer area,.... Milkhouse plumbin' pipin' works Great for such things,....
A 90*, 'n straight length of tubin', to down just above the bottom of the transom,.....
Dead Quiet, til ya start to break over onto plane,....

 

[tfret]

It's a sterndrive I/O, Alpha 1 drive, the drive has the flange for the exhaust bellows, but no bellows and no bellows hole or flange in the transom. My hoses just come off the exhaust manifold risers in a "Z" pattern and out the transom on both sides through a flange that is right on the water line, with flappers on the outside of the flanges. So if I follow what you're saying, I could add a fitting 90* down from where my flaps are and go under water a few inches? I guess put the flaps back on or just leave them off? I've never heard of or seen anyone do this. Some photos would awesome! It sounds fairly cheap and easy to do, and easy to undo also.

 

[Bondo]

or flange in the transom.

Ayuh,...... If it's an Alpha, there IS a y-pipe flange at the bottom of the transom housin', just above the trim lines pocket/ passage,.....

One of these is bolted in-place,....

You'll still need shutters, Somewhere,.....

No pictures, but Ya, attachin' a 90* bend to, or in-place of yer current tips,....
Run down the transom, endin' short of the bottom of the transom, cut 45*, up, 'n aft,....

 

[alldodge]

Don't understand the

no bellows hole or flange in the transom.

The turndowns are like these on my boat

The openings are below the water line so its quite when I come off plane to idle.

 

[Scott Danforth]

all alpha and bravo transom shields have a place for the y-pipe.

 

[Bt Doctur]

 

[tfret]

Wow thanks for the "turn down" photos, thats a cool idea. I'll have to give that a try. Even on plan the sound is being directed down instead of out which has to be an improvement.
Yes, my drive does indeed have the hole for the exhaust bellows. But the transom does not. It only has the hole for the drive shaft. Am I missing something?

 

[alldodge]

Yes, my drive does indeed have the hole for the exhaust bellows. But the transom does not. It only has the hole for the drive shaft. Am I missing something?

If you have an Alpha drive then you have what BT has shown, its part of the transom assembly and the hole has to be cut out for it. There is just a flat plate covering the hole currently

 

[tfret]

Sweet! The boat is in storage right now so I can't run out and look at it. So, is there a blank plate on the water side also? Isn't there a bellows that basically connects the transom flange to the drive upper? Sorry if that's a dumb question.

 

[alldodge]

The block off plate is on the engine side



The exhaust tube or bellows connects the inside Y pipe to the outdrive

 

[tfret]

I think I get it now. I was thinking there were two separate transom holes for drive shaft and exhaust. But there is only a single large hole that the gimbal seals up. And the inside plate seals off water coming in through the unused exhaust port. So I just need the Y pipe to connect there. Please correct me if Im mistaken.
So if that be the case, is there anyway to "horse shoe" the Y pipe in and under the drive shaft without pull the engine? I'm sure I already know the answer but I gotta ask.

 

[alldodge]

I think I get it now. I was thinking there were two separate transom holes for drive shaft and exhaust. But there is only a single large hole that the gimbal seals up. And the inside plate seals off water coming in through the unused exhaust port. So I just need the Y pipe to connect there. Please correct me if Im mistaken.

Correct

So if that be the case, is there anyway to "horse shoe" the Y pipe in and under the drive shaft without pull the engine? I'm sure I already know the answer but I gotta ask.

No way I have ever heard of someone doing it without removing the motor. It's just to tight

 

[Bondo]

is there anyway to "horse shoe" the Y pipe in and under the drive shaft without pull the engine?

Nope,...... I doubt you can even reach the bolts holdin' the block-off plate,.....

 

[Bt Doctur]