Do You Use Resonators in Your Exhaust Lines?

[Richard Seccombe]

Last weekend I blew a hole in 1 exhaust hose in each of the two engines. These are 496 Horizon engines that have one 3 foot exhast hose from each elbow going down to the muffler (2 - 3' hoses per engine).

The hoses are several years old and both blew holes in the top of the hoses about 6" behind the elbows at about 3200 RPM. All of the exhast hoses have what Mercruiser refers to as resonators about 18" from the elbows, or midway between the elbow and the muffler. I am assuming their purpose is to help block any sea water from coming up into the back end of the exhast manifold, but I'm also wondering if they don't cause additional back pressure and heat

Prior to this, I had a combination riser/elbow setup with some cheesy studs going from aluminum manifolds through the risers and bolted to the top of the elbows. I stripped the studs out of the manifolds three times and finally went to cast iron manifolds the extended elbows. This got me out of using the risers and studs and now the elbows are bolted directly into the manifolds. No problem with stripped studs but it makes me wonder if the studs were stripping because of pressure buildup in the exhaust hoses, and the possibilty of the resonators contributing to this.

Sorry for such a long explanation, but I'd really like to hear your opinion on the use of resonators.

 

[Fun Times]

Re: Do You Use Resonators in Your Exhaust Lines?

[B]

Last weekend I blew a hole in 1 exhaust hose in each of the two engines. These are 496 Horizon engines that have one 3 foot exhast hose from each elbow going down to the muffler (2 - 3' hoses per engine).

The hoses are several years old and both blew holes in the top of the hoses about 6" behind the elbows at about 3200 RPM. All of the exhast hoses have what Mercruiser refers to as resonators about 18" from the elbows, or midway between the elbow and the muffler. I am assuming their purpose is to help block any sea water from coming up into the back end of the exhast manifold, but I'm also wondering if they don't cause additional back pressure and heat[/B]
Prior to this, I had a combination riser/elbow setup with some cheesy studs going from aluminum manifolds through the risers and bolted to the top of the elbows. I stripped the studs out of the manifolds three times and finally went to cast iron manifolds the extended elbows. This got me out of using the risers and studs and now the elbows are bolted directly into the manifolds. No problem with stripped studs but it makes me wonder if the studs were stripping because of pressure buildup in the exhaust hoses, and the possibilty of the resonators contributing to this.

Sorry for such a long explanation, but I'd really like to hear your opinion on the use of resonators.

Yes if your boat had the resonators installed then you do need to run them. Read this link about volvo needing them also.http://www.offshoreonly.com/forums/...volvo-8-1-gsi.html?highlight=volvo+hose+blows

 

[Richard Seccombe]

Re: Do You Use Resonators in Your Exhaust Lines?

Thanks Boat Teck,

I pulled up that thread and then did a search on "Mercruiser thru transom bulletin". I came up with this service bulletin: http://www.crownline.net/limiterblocks/om95_09.pdf

If I read it correctly, it says not to use resonators if you are running a thru transom exhaust system which I believe is what I'm doing (elbow to muffler to outside the hull). The bulletin is talking about different Mercruiser engines but includes 454's and 502's.

If you have a moment, please take a look at the link. I'd really appreciate your input.

Thanks,
Richard

 

[Fun Times]

Re: Do You Use Resonators in Your Exhaust Lines?

The bulletin you found covers the out side of the boat only and all that really was for to help with some performance gains really On the bravo 3 stuff. They have too styles of exhaust bellows one is a bellows hooked up to both ends with hose clamps and the other is a tube type that helps with exhaust flow on high performance boats with bravo 3 drives And when you lower the drive that is when it should make contackt from the transom assy to the drive to let the exhaust flow out.Now if your boat does not have the Y exhaust collector on the inside of the boat going down to the rear center of the transom behind the engine, And the exhaust is truly going out the thru transom with exhaust tips and flappers on the inside of the tips to stop water from back flowing to the engine only, Then I have had many people sware they have picked up 1-3 more MPH by taking off the exhaust bellows down behind the drive due to less drag and better flow down there even on the bravo 1 and 3. Now on the resonators it is hard for me to 100% remember right now because I am off work do to a sliped disk injury and all my good info is at work and I can't go get my books to look it up, But what I found here at my home was this link you should read to help you out some.http://www.boatfix.com/merc/mainmenu.pdf When you open it up go to service bulletins, click it, then go to year 00, then open 00-13 and read that. that is the only info I can find here at home but I know there is one more style bulletin out there the dealers have in there system but I believe it is newer then what I could find here on the web at home Sorry I can be of more help on that part. I hope this helps you out some good luck with it.

 

[Richard Seccombe]

Re: Do You Use Resonators in Your Exhaust Lines?

Thanks very much boat teck,

I'll dive into the information on the link you sent and read up. I'm not a big fan of removing anything that can avoid water intrusion but wondered if Mercury came to the conclusion that the resonators were causing more problems then they solved.

The installation manual talks about the maximum psi they want in the exhaust hoses but I'm not sure how I'd go about measuring it shy of mounting pressure meters in the exhaust lines.

Thanks again for the link. I'll dig into it today and hope your slipped disk injury gets better soon.