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Exhaust turn-downs: How deep under water?

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Old 04-25-2008, 09:30 AM
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Originally Posted by VetteLT193 View Post
Every law I've read say that cutouts are illegal. switchable exhaust is not necessarily a cutout.
Yeah, but its a tough fight out on the water, when you have a switch that can make your exhaust loud and quiet; no matter what technology... captain's call, silent choice, quick & quiet, switchable external mufflers. I have had them lean over my dash and ask "What does that muffler switch do?" "Go ahead and start the engines and hitch the switch." It is all total BS.

The law comes from the old car law days when we used to have 'cast iron cutouts' under our muscle cars to bypass exhaust for a little street ripping.
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Old 05-06-2017, 02:28 PM
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Is the silent choice or captain choice etc switchable exhaust ok for a built and supercharged engine? I see them on boats with the 496 and other more stock motors but when you increase the breathing of the engine would these silent choice exhaust be ok?
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Old 05-06-2017, 09:06 PM
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When I had turn downs they ended 6 inches below the water line in gear at idle. To stop the loud pulses I drilled 1/4 inch holes about 2 inches wide and three inches tall from the bottom of the pipes on the side facing the transom. This killed most of the pulse and the splashing.
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Old 05-07-2017, 01:39 PM
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But these turn downs are for at idle only because when the boat is flying at 80 those tubes will be out in the air and the people will hear the thunder and in some cases they will be mad.For me the sound is great but you know how other people can be, they dont have the vision. I was thinking about the inline mufflers in the engine compartment and also with the tips outside with those bolt on mufflers back of the transom
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Old 05-07-2017, 06:02 PM
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I don't have the HP you guys do, but mine are about 6 under. Around 1500 rpms they just start to sound off
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Old 09-26-2017, 07:55 PM
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Default Exhaust Turn Downs

I'm running 1400 hp Teague motors at 110 decibels. I must get the noise down to 90. I just purchased turn downs from Gibson. Any suggestions or concerns I should be aware of?

- Reversion? - Motors stalling at idle? - How deep should they be? - Back pressure relief holes?

Any suggestions would be helpful. Thanks
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Old 09-27-2017, 01:05 AM
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Originally Posted by turbos230 View Post
But these turn downs are for at idle only because when the boat is flying at 80 those tubes will be out in the air and the people will hear the thunder and in some cases they will be mad.
LOL . who will be mad snail boaters and fisher****ers?
**** em
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Old 09-27-2017, 01:06 AM
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Quote:
Originally Posted by GK View Post
I'm running 1400 hp Teague motors at 110 decibels. I must get the noise down to 90.

Any suggestions would be helpful. Thanks
Don`t buy 1400hp motors if you need to be under 90db.

Hope this helps
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Old 09-27-2017, 04:08 AM
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I am interested in adding downturns to mine ( merc 700's ) mostly for noise at the docks....
up and running / offshore, I don't mind making some noise.

I would also interested to hear peoples real world experiences with them and how they engineered them.
I have seen many "big power" boats on OSO with them
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Old 09-27-2017, 06:40 AM
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Here is a custom CMI underwater kit. For sale too.
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Exhaust turn-downs: How deep under water?-cmi-kit-015.jpg   Exhaust turn-downs: How deep under water?-cmi-kit-014.jpg   Exhaust turn-downs: How deep under water?-cmi-kit-013.jpg  

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