OK I'm Going to Try the Exhaust Flapper Experiment

[sean.deangelis]

I know I'm going to get flamed for this but:

I saw a few threads asking if an exhaust flapper, intended for the outlet on thru-hull exhaust can be mounted on the transom plate exhaust outlet in place of the bellows or boot. I have a 99 Four Winns H200 with the Gi 305, SX drive. I had the OEM accordion style bellows on the outdrive originally. Then this winter I did a bunch of maintenance and replaced the accordion type bellows with the rubber "boot" that directs most of the exhaust to the inlet on the lower unit and out through the prop. The result was same level of quiet at idle and a slightly increased V8 noise on plane.

Now this weekend because the wife and kid are out of town and I'm feeling the itch to nerd-out on a few boat items I'm going to remove the "boot" and replace with an exhaust flap...all for fun.

I'm going to look at engine temperature at idle and on plane and compare before and after. I'm also going to pull the boat after a 30 minute run on plane and see if there is any burning, discoloration or other undesirable effect after running the flapper. I have a nice "laser" temperature gun that I could use to check temperature on various surfaces of the lower unit but I doubt seriously that it will work through the surface of the water.

What am I looking for? I guess the hillbilly side of me wants to make a little noise on the lake...perhaps I just need the attention. In any case I have the free time and I want to know if this will work.

 

[sean.deangelis]

Re: OK I'm Going to Try the Exhaust Flapper Experiment

Experiment complete. Result is no measurable change in engine temperature on plane or at idle. Noise increased slightly on plane. No discoloration or other undesirable effects to the outdrive. Think I'll leave it this way until later spring when the houses on the lake start being occupied again. In any case hopefully this helps someone's Google search in the future.

 

[bajaunderground]

Re: OK I'm Going to Try the Exhaust Flapper Experiment

Sean, can you post some pictures of your experiment? Not that I'm too interested in making more noise, just curious?

Thanks,

~Brett

 

[sean.deangelis]

Re: OK I'm Going to Try the Exhaust Flapper Experiment

Sure thing. Looks like this now:

 

[MikDee]

Re: OK I'm Going to Try the Exhaust Flapper Experiment

Question, Wouldn't this be even louder with the boot, vs. the flapper? You're taking an open pipe (boot), and putting a flapper over it?

 

[sean.deangelis]

Re: OK I'm Going to Try the Exhaust Flapper Experiment

Question, Wouldn't this be even louder with the boot, vs. the flapper? You're taking an open pipe (boot), and putting a flapper over it?

No. The boot is an interesting setup: It clamps to the exhaust outlet on the transom plate assembly. It is somewhat rigid and the opening at the lower unit side is slightly larger than the exhaust inlet port on the lower unit. So when you trim down from "trailer mode" the larger/aft part of the boot sleeves over the exhaust inlet on the lower unit. That way most of the exhaust gas travels the normal route and out through the prop. There is only about 1/8 inch of space all the way around between the boot and the exhaust inlet on the lower unit. As you articulate the trim up and down through the "usable" portion of the travel the boot still covers most of the exhaust inlet on the lower unit (it's about 2 inches long).
So to clarify: with the boot setup you are never sending exhaust gas straight out into the atmosphere save for the little bit that gets out around the fitment between the boot and the inlet on the lower unit. Unless you were to run the boat with the trim waaaaaaay up (which is bad for another set of reasons).

What I need to do is wakeboard behind the boat. Like I mentioned earlier the boat is not that loud with the flapper installed however, I'm judging that from inside the boat. Once the water is a little warmer I'm going to wakeboard behind the boat. If it's absurdly loud from there I'm going back to the boot.

 

[bajaunderground]

Re: OK I'm Going to Try the Exhaust Flapper Experiment

Being as the whole assembly is underwater, doubtful it'll be too loud or objectionable? Out of the water, I bet it's slightly louder, but not significantly? Am I correct in thinking you removed the internal exhaust flappers? Not sure I read the initial post correctly?

As long as there's no opposite effect (affect?) i.e. becoming blocked or allowing water to reverse up the Y-pipe, I don't think this is a huge mod....as long as the factory bellows are not disintegrated, having holes in the (which they have when new for water drainage?) is okay.

Sounds like you need some "Captain's Call" exhaust?

 

[midcarolina]

Re: OK I'm Going to Try the Exhaust Flapper Experiment

Any more info on the flapper? part # or where you purchased it from?

 

[Thalasso]

Re: OK I'm Going to Try the Exhaust Flapper Experiment

I am told by the dealer that the newer Volvo's don't even put a boot on. It's a directional pipe per say faced down. Little louder but not by much.

 

[sean.deangelis]

Re: OK I'm Going to Try the Exhaust Flapper Experiment

Any more info on the flapper? part # or where you purchased it from?

The flapper I got on Amazon for $20. Telflex Marine part number 18-4456.
The "boot" I initially installed I purchased on VolvoPentaStore.com. It is VP part number 3587641.

 

[sean.deangelis]

Re: OK I'm Going to Try the Exhaust Flapper Experiment

Being as the whole assembly is underwater, doubtful it'll be too loud or objectionable? Out of the water, I bet it's slightly louder, but not significantly? Am I correct in thinking you removed the internal exhaust flappers? Not sure I read the initial post correctly?

As long as there's no opposite effect (affect?) i.e. becoming blocked or allowing water to reverse up the Y-pipe, I don't think this is a huge mod....as long as the factory bellows are not disintegrated, having holes in the (which they have when new for water drainage?) is okay.

Sounds like you need some "Captain's Call" exhaust?

I'm lead to believe that on my vintage (1999) VP SX drive there are no internal flappers

At idle with everything submerged there is no noticeable increase in noise at all. What I was surprised to notice was that basically the entire transom plate and gimbal housing are out of the water when cruising...which made sense after I thought about it I just had never noticed.

I would love a captains call but beside the cost I have an issue: The Four Winns Horizon has a very different transom than most boats. The actual transom is about 20 inches forward of the stern line of the boat. They call the resulting shape "planing surfaces." Whatever the reason for the design it makes routing a through transom or through hull exhaust really difficult. To run them out the back I'd have to offset the pipes inward until they were about 4 inches apart. To run out the sides of the hull I'd have to modify the inner engine housing, relocate the battery and possibly even route the pipes forward slightly before turning them back to the 45 degree angle out the sides.

To be frank I have my eye on an older FW Liberator that needs repowered, transom, floor and stringers replaced. I think that will be the boat I really nerd out the exhaust on. I'm thinking captains call with catalysts and mufflers after conversion from OMC to MC 502.