OK I'm Going to Try the Exhaust Flapper Experiment

sean.deangelis · **Posted:** Wed Apr 09, 2014 8:59 pm

OK so I've searched several forums looking for answers on the 'great exhaust debate' with little luck. At first I was interested in a captains call or similar but seemed pointless given the cost. I want a louder exhaust note from my 5.0Gi for no good reason in particular but nothing permanent.
So when I was doing my spring maintenance last month (I live in Georgia where spring has already sprung) I replaced the OEM "accordion" style exhaust bellows with the VP rubber "boot" type outlet (VP part number 3587641). The boot directs most of the exhaust gas/noise to the inlet on the lower unit and out the prop. The result was a slightly increased noise on plane and of course no noticeable difference at idle.
So then I get curious wondering if I can just install an exhaust outlet flap, like those used on the outlets of a thru-hull exhaust, right on the exhaust outlet on the transom plate assembly. Found a used one online and this weekend I'm going to test things out. Mostly I want to make sure engine temps stay at normal levels and that after an extended period on plane nothing looks cooked.
In any case I'll post me findings so hopefully in weeks/years someone else Goggling this info can get an answer here.

schoolsOut · **Posted:** Wed Apr 09, 2014 9:14 pm

I've read that you can just remove the exhaust bellows and skip the flapper. Maybe someone can verify.

sean.deangelis · **Posted:** Wed Apr 09, 2014 9:22 pm

I considered that but I had this bad image in my head of coming off plane, to a stop and 1 of 2 bad things happens:

1 - water gets forced up the outlet hard enough to break the internal flapper loose and cause a problem
2 - water gets forced up the outlet hard enough to cause a stall

Both pretty far fetched scenarios but I'm a bit neurotic lol.

LouC · **Posted:** Wed Apr 09, 2014 11:28 pm

There are no internal flappers, Volvo eliminated them years back on the SX models. I'd just leave it the way they designed it. There is no easy to fit an external flapper to those like the AQ drives had.

deafwish · **Posted:** Thu Apr 10, 2014 1:56 am

I used an external exhaust flap & have not had an issue in the 50+ hours use, including stationary fishing in rough water.

Buy something like this:
http://www.hardin-marine.com/p-13183-3- ... apper.aspx

LouC · **Posted:** Thu Apr 10, 2014 6:10 am

Well looks like I stand corrected, actually I think that's a good way to correct Volvo's removing the flappers in the Y pipe. Just like a through the transom exhaust flapper.

rpengr · **Posted:** Thu Apr 10, 2014 8:38 am

sean.deangelis wrote:

I considered that but I had this bad image in my head of coming off plane, to a stop and 1 of 2 bad things happens:

1 - water gets forced up the outlet hard enough to break the internal flapper loose and cause a problem
2 - water gets forced up the outlet hard enough to cause a stall

Both pretty far fetched scenarios but I'm a bit neurotic lol.

Neither one of these will happen while the engine is running. There is plenty of exhaust pressure while the engine is running.

My concern would be sitting in waves with the engine off. Such as drift fishing in rough seas, or when multiple people are sitting on swim platform and subjected to waves. For these reasons, I would use the flapper.

sean.deangelis · **Posted:** Thu Apr 10, 2014 7:42 pm

Well everyone pretty much nailed it. No noticeable difference in temps, no indication of anything amiss. Sound slightly improved. I'm a happy guy

meinmelb · **Posted:** Tue Jul 01, 2014 10:08 pm

Hi Sean and Defwish

It seems you have both installed the exhaust flapper on the outside of the transom by removing the bellows, eliminating the need for the exhaust gasses to exit through the prop. I will be checking the internal exhaust flappers this weekend as I suspect they may have broken and lodged in the exhaust passage somewhere killing the power. If I am pulling off the bellows it would be a simple job to install this external flapper and not reinstall the bellows? I also plan not to replace the internal flappers if I install this. The motor is the Merc V6 4.3mpi with an Alpha 1 drive.

Could you answer a few questions for me please?
1. What was the noise increase, can you still have a reasonable conversation on the boat while under way?
2. Was there any Power increase that you can feel?
3. Is there increased black residue from the exhaust on the rear of the hull/ under the swim platform?
4. Did you notice any difference in the wake with no exhaust gas in the prop wash?

Then do you know what size the exhaust hole is exiting the transom and how long did it take you to remove the bellows and install this?

I appreciate your feedback.

Thanks!

deafwish · **Posted:** Wed Jul 02, 2014 3:15 am

meinmelb wrote:

Could you answer a few questions for me please?
1. What was the noise increase, can you still have a reasonable conversation on the boat while under way?
2. Was there any Power increase that you can feel?
3. Is there increased black residue from the exhaust on the rear of the hull/ under the swim platform?
4. Did you notice any difference in the wake with no exhaust gas in the prop wash?

Then do you know what size the exhaust hole is exiting the transom and how long did it take you to remove the bellows and install

1: Certain load RPM's can be 50% louder, while most loads are only 15%.
I find that just before planing speed is the loudest, as it resonates under my swim platform. No biggie as you can still easily speak quietly to one another.
2. No. You'll need 50hp to notice anything on a boat!
3. Hardly. Easily manageable when hosing down the boat.
4. I assume there'd be less fumes for knee boarders and tubers. Wake boarders would be standing too tall.

I can't recall the size, but think it's around 3".

Jdpber · **Posted:** Wed Jul 02, 2014 1:24 pm

this sure is a great solution to the exhaust bellow. may give this a try.. also if you have not looked and measures detailed these boats are very hard to install Captains call as mentioned above (wanted for the cool factor of making noise) basically why i want it also.

well the easy and cheap solution is 3" straight out the transom. NOPE the damn power steering ranch is in the way and cannot use a riser topper on the manifolds to gain the 2.5" needed bc then you hit the built in platform. so the cheap way is now gone.. So for the horizon boats side exit is all that is left and thus you have to sit a more detailed oval cut, not too hard but you cannot buy a 3-4' hole saw bit to do this. then the added piping. rats i have batteries in that location.. thus lies it is not worth the 2k needed for side exit on this hull design. MY NEXT boat i will factor in preexisting CC and the spacing for upgrading to CC. AS i like loud boats..

but for now ill take a $10 gamble on the flapper. hell even if it only sounds better getting on plane.

rpengr · **Posted:** Wed Jul 02, 2014 1:37 pm

When I was 6 years old, I would clip playing cards to my bicycle frame so that the spokes would flap the cards and make noise. A month later I had outgrown the need to make such noise.

...Maybe by the time you buy your next boat, you will have outgrown the desire to be "cool" by making a lot of sound pollution. I don't think straight pipes should ever be used on a boat except in sanctioned racing.

I think it is cool when people walk up to my boat and can't tell the engine is running.

LVChris · **Posted:** Wed Jul 02, 2014 2:33 pm

rpengr wrote:

When I was 6 years old, I would clip playing cards to my bicycle frame so that the spokes would flap the cards and make noise. A month later I had outgrown the need to make such noise.

...Maybe by the time you buy your next boat, you will have outgrown the desire to be "cool" by making a lot of sound pollution. I don't think straight pipes should ever be used on a boat except in sanctioned racing.

I think it is cool when people walk up to my boat and can't tell the engine is running.

+1

LouC · **Posted:** Wed Jul 02, 2014 3:02 pm

True, true, one of the attributes of I/Os is that they are quieter than old school 2 stroke outboards by a lot, and the sound they make is more pleasant. Four stroke OBs are actually quieter idling, but at speed a bit higher pitched.
The guy who runs the local boatyard used to have a 45 foot Apache cigarette style boat, with twin big blocks and outside exhaust. I could hear him start it from my house if the windows were open and when he hit the end of the channel and opened it up, it resonated across the bay. Not that I minded it but after a while that would give you a headache. When I go to Englishtown (drag racing) for the Summer Nationals I wear ear muffs for the funny cars and top fuel dragsters (6000 hp blown nitro burning Hemis). Love the sound, just not the volume....

andrewsc · **Joined:** Mon Jul 07, 2014 6:38 am **Posts:** 11

I'm curious to confirm, this is mounted on the out drive side of things? Hard to tell by the picture.

www.iFourWinns.com

OK I'm Going to Try the Exhaust Flapper Experiment

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