Engine Exhaust Flap

[TBMsNautique]

I have a single exhaust on my 2000 SS and the flap fell off this past weekend. Is this a necessary item to have (e.g. carbon monoxide deferral?) or is it primarily for noise reduction? Actually, I like the sound without it. The boat is always stored on a lift but we sometimes float around in the open water while the kids swim off the back. Thoughts are greatly appreciated.

[SGY]

RE: Engine Exhaust Flap

Not sure, but I think one of the reasons for the flap is to keep water from running back into the exhaust.

[FLCERIK]

RE: Engine Exhaust Flap

Yes it is required to have. If the water runs back into your exhaust it can cause damage.

[Andrew]

RE: Engine Exhaust Flap

no, its not required.....
none of the older cc's had them, and inboard boats with "non-flapped" exhaust have been around quite some time. water will not flow up the exhaust when the engine is running, and u can't back up fast enough to force water all the way to the manifolds without the engine running......

with that being said, do not tow ur boat backwards without a flap (which would be pretty hard to do lol) other than that, feel free to run it without a flap

[TBMsNautique]

RE: Engine Exhaust Flap

Thanks very much for the reply. This is what I thought given how high the water would have to flow to cause problems. As I said earlier, the sound is terrific without the flap!

[sanddragon2004]

its not when the boat is running u need to worry about, its when the boat is sitting idle and a big boat or wakeboat drives by and throws a wave your direction. the force of that wave action can force water up in the motor. This is a very common issue with ddrive ski boats, less of an issue with nautiques because of the single exhaust and the muffler.

I myself have replaced and seen several motor jobs come into our shop because of this problem.

my advice, spend the 20 bucks to replace it.

[Andrew]

ok, in order for water to flow up into the manifolds from a passing wake, the wake would have to be over the manifold AND the boat would have to remain at the same height (which will be impossible if it is still in a "floating condition")......... as i said before, its gonna be very hard for water to flow up the tube and into the manifold. u'll pretty much have to try and even then it will still take some effort

do the math on the amount of pressure that it will take to force water into a 4"? (i dunno how large the single exhaust is...) and up about 1-2ft............ hint: ALOT

[OM45GE]

You could probably live without it, but $25 vs $4,000 +++ for a motor seems like a no brainer. I also had a problem on an older Master Craft with no flaps when field mice found the exhaust a nice nesting place for the winter. The boat wouldn't start in the spring because and we had to disassemble the exhaust to get all the debris and dead critters out of it.

[DanielC]

When you shut your engine off, the hot exhaust gas cools, and takes less volume. This sucks water into the exhaust system. If there is any steam in the exhaust system, it will suck more even water, especially if the engine overheats.
www.skidim.com has exhaust flaps.

[ag4ever]

The wave does carry some energy to surge some water into the exhaust, but I seriously doubt it would have any where enough energy to fill the muffler and then keep moving to the manifolds.

Even if the exhaust cooled to freezing, there will not be enough negative pressure to bring the water into the manifolds. I would be more worried about the water vapor condensing in such a cold environment.

[SquamInboards]

ok so it's rare but it happens. While it may be incredibly unlikely, it's infinitely more likely that problems will occur without the flap. You'll probably never get mauled by a bear, either, but if you run around chasing bear cubs and taunting the mother.... you get the idea, it's worth the $25 to stay out of trouble.

[SGY]

The flap might keep the critters out too.

[FLCERIK]

I am sure the engineers at CC put a flap on the exhaust for a reason. You are better off safe than sorry.

Why would you want the exhaust to be loud? All it does is make it difficult to hear eachother talk or listen to the stereo. If you want a loud exhaust you should consider buying a bumble bee at Pep Boys and doing a custom modification. That would be awsome... Or another option would be to buy a flatbottom with a supercharged chevy 454 with straight headers. If the flatbottom has a jetivator consider it a bonus. You would be the man..

[tdc_worm]

the one thing nobody is considering is that the water has to displace the air that is already in the sealed exhaust system. there is no possible way that incoming water could a) compress the air enough to reach the heads or b) cause enough pressure to force the air to make the crankshaft rotate, which would allow the air an escape route.

you can get stainless exhaust tips on a malibu, and i am quite sure that indmar has done enough homework to keep from warrantying malibus if this indeed was an issue. on the moomba that i had, the flap was just that: a rubber flap that sealed nothing going either in or out.

my main concern would be the birds that and other varmints that may find it to be a suitable nesting hole when it was on the lift...

[Andrew]

the one thing nobody is considering is that the water has to displace the air that is already in the sealed exhaust system. there is no possible way that incoming water could a) compress the air enough to reach the heads or b) cause enough pressure to force the air to make the crankshaft rotate, which would allow the air an escape route.

you can get stainless exhaust tips on a malibu, and i am quite sure that indmar has done enough homework to keep from warrantying malibus if this indeed was an issue. on the moomba that i had, the flap was just that: a rubber flap that sealed nothing going either in or out.

my main concern would be the birds that and other varmints that may find it to be a suitable nesting hole when it was on the lift...

agreed, but u'll never convince some people..........