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Old 04-07-2008, 03:29 PM
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Default Decibels

When you use mufflers,what is their impact on the engine noise level?Have you any stats?Is it possible to stay under 90 decibels?

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Old 04-07-2008, 05:21 PM
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Silent choice knocks my WOT about 10 knots. I am curious to know what Silent Thunder does. Not very scientific but My Formula 382 w/ 500HP Blue motors does 74 by GPS on flat water. Mine is a 99 with stepped hull. Anyone with a comparable Silent Choice Boat?
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Old 04-07-2008, 08:11 PM
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Warning!!!! If you have Merc Blue Motors, especially 525's, do not run your diverters over 1500rpm let alone WOT. Reversion is usually the result. And even though Corsa and other companies say you can run up to 3000 or 3500 rpm, don't do it with a 525 or probably even a 500. Someone here lost 2 new 525's because of a miscommunication about this very issue. Get external mufflers if you have to quiet it down. Getting under 90 can be done though. I think CMI makes some that can get down to that level. There are others out there though. It really depends on what motor(s) you have and how loud they are to begin with.
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Old 04-07-2008, 08:32 PM
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Quote:
Originally Posted by UNSANE View Post
Warning!!!! If you have Merc Blue Motors, especially 525's, do not run your diverters over 1500rpm let alone WOT. Reversion is usually the result. And even though Corsa and other companies say you can run up to 3000 or 3500 rpm, don't do it with a 525 or probably even a 500. Someone here lost 2 new 525's because of a miscommunication about this very issue. Get external mufflers if you have to quiet it down. Getting under 90 can be done though. I think CMI makes some that can get down to that level. There are others out there though. It really depends on what motor(s) you have and how loud they are to begin with.
I would think it's more of a backpressure problem at higher rpms. The threat of reversion is at lower rpms close to idle speeds.

But I could be wrong!
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Old 04-07-2008, 09:24 PM
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It happened on the sea trial. The former owner was driving the boat and we were puzzling over why we were going so slow. Pardon my ignorance but what is reversion?
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Old 04-08-2008, 10:45 AM
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It happened on the sea trial. The former owner was driving the boat and we were puzzling over why we were going so slow. Pardon my ignorance but what is reversion?
water entering the cylinder. It can happen several different ways. To much backpressure could put some in there as well I believe. This is why it's dangerous to run diverters closed on a 525 at high RPM's because if I understand its valvetrain correctly, the valves are open a long time (secret to its power) and water might be able to get back in there. This happened to someone on the board and there was a big legal issue between Merc, CMI and Corsa about who was to blame since Merc didn't want to deal with the engine that I believe was under warranty. I called Merc and they told me not to run diverters above 1500 RPM because of backpressure and reversion problems.

Reversion can also happen with leaky headers and water can get back into the cylinder while running or even sitting after running. (why I drain my headers every time)
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Old 04-08-2008, 10:58 AM
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Thanks for the tip. My motors are 500's but it sounds like a problem for any motor
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