Loud SX outdrive

[smassey22180]

I just upgraded to a different boat and went from a MC Alpha 1 to a VP SX. My new boat is silent on idle. I can barely hear the engine run. But once on plane it sounds like I am on muffs in the driveway. On muffs I can hear some of the exhaust coming out of the prop but most of it comes out the outdrive from these square cut out areas in the picture below. No water comes out these holes. Most water comes out the transom with a little coming out the prop. Is this normal for VP to be this loud? If there is a plug where is the most common area to look? I assume I should separate the upper and lower. I removed the prop and did not see anything there.

 

[skydiveD30571]

Someone will know better than me, but I've never seen these holes on an SX drive before. I wonder if it's possible someone cut them to make the exhaust louder.

 

[garbageguy]

No holes like that on my VP SX (1998 Wellcraft, assume drive is about same year)

 

[BRICH1260]

On my last boat, `02 VP SX, I had exaust holes there. I am betting for some reason that your prop is not drafting the exaust down and through the prop hub at speed. Separating the upper from lower might yield some answers, or perhaps run a bore scope up in there to see if you find any obstructions. If boat hasn`t been ran in awhile, mice or mud daubers may have gotten up in there and built a nest, clogging the passage.

 

[smassey22180]

I checked Google images and other SX outdrives have the same square holes. I am starting to wonder about my prop. It is an aftermarket with what looks like an adapter hub (see attached). It is a 14" 17p so I am currently looking for an OEM 14.75" 19p. I hit 5200 rpm at WOT. Thanks

 

[Mnoverboard]

Hello, I went from a merc to Volvo penta this summer (same engine and sx drive as yours) and it is noticeably louder than the Mercruiser. I'm sure the drain holes in the exhaust bellows play a part. Take a peek in that hole like Brich says. WOT seems a bit high, think spec is 4600-4800rpm. My OEM prop is 14.25x21 and keeps it within range. Cheers

 

[HorizonblueDK]

I'm pretty sure I have seen a block-off plate kit made by Volvo, to close exactly these holes. But searching a bit, I can't find it. One reason for having these holes could be that if you rev up the engine in reverse, some exhaust will exit through the prop and disturb the water and cause less thrust. I have seen this explaination somwhere.

 

[smassey22180]

Finally got separate the upper and lower and there was nothing in there. I was really hoping to find an old flapper but no luck. It's almost like the V on the bottom of the boat is keeping that part of the out drive out of the water. My last boat had a flat 1 foot wide section at the back. This boat is V all the way back,

 

[jerryjerry05]

The hull configuration shouldn't have anything to do with the noise.
The Volvo exhaust bellows has holes cut into the bottom of some of their bellows to help get rid of the water and gasses.
That's probably where the noise is coming from.

 

[smassey22180]

I still have the original old style exhaust bellows. Is the new style noisier?

 

[bruceb58]

If your exhaust bellows don't have huge rips in them, they aren't the cause of the noise. The holes/slits are tiny to allow water to drain.

 

[Tail_Gunner]

I still have the original old style exhaust bellows. Is the new style noisier?

The bellow has nothing to do with the exhaust note, Notice those large rectangular shapes they are the primary exhasut dump's notice one thing they are very close to the top of cav plate...read easy to hear loud close to the top etc...and yes the prop does exhaust to but its not like a merc drive.....Treat you engine to some sea foam and you will notice about 80% of the oil burn will come from the exhaust port's on that lower cav plate.


OK here's a static pic of exhaust flow on a sx drive

 

[bruceb58]

Amazing how much smoke snake oil makes when it burns!

 

[smassey22180]

I guess I am going to just have to live with this. The noise sounds just like an Alpha 1 with some marsh grass stuck across the outdrive. It is not so bad at 3k rpm but not good at all at 5k. Ultimately it is going so save me some fuel .

 

[Tail_Gunner]

Amazing how much smoke snake oil makes when it burns!

..........You have that right....:lol: and that's at idle. I live in a neighbor that take's a very dim look at such...thing's. its no longer a practice.....water burn's much cleaner. Ohh and by the way my valve's are shinery than your's....