05-13-2014, 10:55 AM #1
Resonators... what do you know about them? Differences?
Seems like most of the late model skis came with the plastic resonators in the exhaust to help tame down the exhaust noise. These came in a variety of sizes and shapes to fit in the various different hulls.
My Rio has the 1200 carb'ed Virage TX engine and waterbox in it... but no resonator. I have plenty of room to use any one I want... so I'm looking to learn more about them to pick the right one.
So let's talk resonators.
Are resonators "tuned" to their specific engine?
Does a the resonator size equate to it's noise dampening ability?
How does the number of baffle chambers or their length in the resonator affect things?
Are the skis with dual resonators (Genesis) quieter?
Do the dual resonators still use the same common exhaust hose size (3in?)... or are they smaller since they split off into two?
Are DI engine resonators different?
Which would be the best to quiet the exhaust the most?
Thanks for sharing what you know.
05-13-2014, 01:17 PM #2
- Join Date
- Jul 2007
- near Toronto, Canada
This is my understanding of how these resonators do what they do. This is off the top of my head, so I am sure I will forget some stuff and will of course omit things I don't know that I don't know.
Other than the Weber turbo engine, for which I have no idea whether the resonators are different, the primary engine Polaris used resonators with (2000-2004) is the '1200'.
There were three versions of the 1200 engine, mounted in three different hulls. Virage, Genesis* and MSX 140. The three 1200 engine's are the red 1165cc carburetor, red 1165cc Ficht fuel injected, and the black 1195cc MSX 140 fuel injected.
There are also resonators in the two cylinder Virage i and Virage. Not sure about the Freedom (and too lazy to go look at the parts diagrams).
What happens is each individual exhaust pulse travels down the main tube of a resonator and the sound/pressure pulses also travel down the small internal resonator tubes that branch off from the main exhaust flow path. Just like a tiny version of a tuned red exhaust pipe, these pressure pulses reach the ends of the individual resonator tubes and reflect back towards the main section.
The key is that each individual resonator molded tube is a slightly different length so the reflected pressure pulses arrive back at the main section at slightly different times. These out of phase return pulses have the effect of softening the sharp exhaust pressure pulse and spreading it out in time. The softer the pressure pulse when it reaches the hull exit, the less loud the exhaust sound is. The sound is more diffused and the sharp, higher pitch engine notes are subdued.
It is called a resonator since each small tube resonates at a specific frequency.
Each molded resonator tube has a different internal length and it affects a narrow range of sound frequencies. To achieve sound reduction over a wide range of audible frequencies, a bunch of resonator tubes of many lengths are needed. Within reason, the more different length resonator tubes the better.
Polaris had to mold the resonators into weird shapes not only to fit them inside the hulls but also to add as little extra length to the main exhaust flow path. Even though the resonator main sections are wide open from end to end, if you add together too many it still acts like a mildly restricted exhaust.
To retrofit these resonators to a different hull (Rio boat hull) I would select two or three that together provide a wide range of resonator tube lengths. I think some models had three different resonator sections from the factory, this would be a good place to start. If you want to add even more sections choose ones with tube lengths that differ somewhat from the others.
The resonators themselves will emit sound from their exteriors, so mounting them in a manner that allows you to acoustically enclose (wrap) them should help reduce overall sound levels. The factory PWC hulls did this using the foam inserts and of course the sealed seat on top.
* The 1999 Genesis had an unusual exhaust arrangement with two exhaust exits, both mounted below the waterline on the hull bottom. I have not studied the 1999 Genesis exhaust but I think it did not utilize resonators.
05-13-2014, 10:18 PM #3
Thanks K! Good info.
Do the tubes section of the resonator need to higher than the main through-pipe section... so as to not collect and trap water in them?
05-13-2014, 10:51 PM #4
- Join Date
- Jul 2007
- near Toronto, Canada
05-14-2014, 06:08 AM #5
hi, on this virage hull i bought there are 3 resonators. the 3rd and last one sits just before the hull exit pipe is a single resonator and very well hidden in the hull. it looks as tho it sits below the hull exit tube thus holding water. (might be wrong there and will double check).
would also add that they can be easily welded to make your own sizes as i have just found out.
connector tubes are 68mm wide internal measurement, a 4 ply standard round tube normallly has a 5 mm wall making them 78mm pipes, just in case you need to make your own connectors and they are available on ebay.
hope this helps a little..
06-15-2014, 08:53 PM #6
- Join Date
- Sep 2006
- San Juan, Puerto Rico, Puerto Rico
If we remove the resonator improved rpm, or that the results would be to eliminate
06-15-2014, 09:56 PM #7
- Join Date
- May 2008
- Elephant Butte New Mexico
I am weary of dealing with resonator problems. The labor is extreme in most of the cases.
They do help keep the peace with neighbor and boaters, and they were required for epa sound compliance, but marketed like they would save the planet.
They are pretty pricey. I'd go with some tuned pipes or any performance water box before considering a resonator approach, unless it's on a small lake with dodgy neighbors.
They tend to shatter at the smallest of backfires(used ones can be brittle) or melt if your engine is running a little lean.
There should be some neat solutions for using a water controlled muffler box ala Seadoo on a Polaris setup. I just recently became aware of the rio. Nice rig
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