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Old 12-29-2015, 01:15 PM   #1
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Default Exhaust Flappers

On the topic of exhaust, the flappers in my Y-pipe (twin 1994 7.4Ls) are not in the best of shape. One was broken in half (missing half not found) and the others don't swing so easy. These flappers look like just a brass plate with some rubber coating that hinges on a pin. All the new flappers I see appear to be a caged assembly where the flapper is two flaps that both blow down whereas my old ones are a solid piece where one end goes down and the other up. So, these new style ones look even more restrictive to the exhaust.
Questions-
Am I seeing the pictures right? Are these new flappers right for my boat? Will they hurt performance at all? Bigger question I guess is do I really even need them? when would water back up into the engine and do these flappers actually seal well enough to prevent that?
Sorry for the long post, but I'd appreciate any insight.
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Old 12-29-2015, 01:30 PM   #2
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The ones you are finding are correct and the only style I have seen.

The pipes diameter is large enough that no performance loss occurs.

Yes they are required for cases of coming off plane quickly as the wake collapsing can force water up the exhaust. While a little water can get past the flapper its job is to prevent an amount that would flood the engine.

I say replace them.
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Old 12-29-2015, 01:34 PM   #3
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The ones you are finding are correct and the only style I have seen.

The pipes diameter is large enough that no performance loss occurs.

Yes they are required for cases of coming off plane quickly as the wake collapsing can force water up the exhaust. While a little water can get past the flapper its job is to prevent an amount that would flood the engine.

I say replace them.
I thought that was the intent of them, but thought the exhaust would keep the water out. I'll order them; thanks for the quick reply!
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Old 12-29-2015, 01:40 PM   #4
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Moved to new thread as post was hi-jacking another thread.
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Old 12-29-2015, 01:51 PM   #5
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Quote:
Originally Posted by mmwjr View Post
The ones you are finding are correct and the only style I have seen.

The pipes diameter is large enough that no performance loss occurs.

Yes they are required for cases of coming off plane quickly as the wake collapsing can force water up the exhaust. While a little water can get past the flapper its job is to prevent an amount that would flood the engine.

I say replace them.
Ok, microfiche says use the second pictured flap, but I found somewhere it said it doesn't work when the original flapper was pinned. Part number 807166A1
Is the first picture what I want? Part number 807166A3
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Old 12-29-2015, 01:53 PM   #6
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Quote:
Originally Posted by mmwjr View Post
The ones you are finding are correct and the only style I have seen.

The pipes diameter is large enough that no performance loss occurs.

Yes they are required for cases of coming off plane quickly as the wake collapsing can force water up the exhaust. While a little water can get past the flapper its job is to prevent an amount that would flood the engine.

I say replace them.
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Moved to new thread as post was hi-jacking another thread.
Sorry, thought it was relevant.
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Old 12-29-2015, 07:13 PM   #7
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I thought that was the intent of them, but thought the exhaust would keep the water out. I'll order them; thanks for the quick reply!

At high rpms the exhaust gas may keep the water out however when backing down off plane the throttle is cut back and the exhaust gas pressure drops too low to prevent water ingestion.
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Old 12-29-2015, 07:15 PM   #8
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Ok, microfiche says use the second pictured flap, but I found somewhere it said it doesn't work when the original flapper was pinned. Part number 807166A1
Is the first picture what I want? Part number 807166A3

Not 100% sure but I think the first picture is the one you want. Check the manual for your boat.
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Old 12-29-2015, 07:19 PM   #9
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Not 100% sure but I think the first picture is the one you want. Check the manual for your boat.

They didn't make these new style flappers in 1994. They no longer make what my boat came with. That's why I asked..
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Old 12-29-2015, 07:23 PM   #10
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They didn't make these new style flappers in 1994. They no longer make what my boat came with. That's why I asked..
If I recall correctly the new style are designed to replace the old ones.
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