Amuse Helmholtz resonator dimensions
 

Does anyone know how the length/diameter of the Helmholtz resonator on the Amuse exhausts compares to our OEM Helmholtz resonator?

I'm considering having one fabricated to match up with my J's 70rs single to reduce/eliminate 3-5K cruise/deceleration drone.

The optimal size of the Helmholtz resonator is based on the exhaust system's volume and I figure a 70mm Amuse single is closer to the J's 70rs than the OEM system. I've seen pictures of the two side by side and it appears that the Amuse Helmholtz resonator is larger.

Posted too early. Found the info. after an extensive search:

Distance from cat to centre of pipe: Stock 240mm, Amuse 220mm

Length: Both 150mm

Diameter: Stock 45mm, Amuse 55mm.

Location: Is similar both on the Amuse and on stock pipe. Guess that is the best place to put it.

did you ended up adding this to your J's exhaust? Does it work?

Im thinking to do it on mine...

I'm doing exactly this to my Greddy Ti-C. Will report back later this week.

Please do report back... Planning to do this when I install the test pipe

OK, so I added the Helmholtz to the Greddy Ti-C. It quieted down the cabin to sound more like it does with the silencer in when at RPMs below 1500. Between 2500 and 2800 there is minimal drone, and it sounds like there is an ANR headset (like a Bose QC3) that was turned on for that narrow band. After 2800 RPM the exhaust gets louder again, but is not as intense as without the Helmoltz resonator. I have autocross videos to confirm that the sound is the same. HP feels the same with the Helmholtz, and that makes scientific sense, whereas I noticed a slight increase over stock with the Greddy.

Pics are below. I am considering lengthening or shortening the resonator to raise the effective band to about 4,000 rpm which is where I normally cruise. I guess longer is the right way, but I am not sure. With my exhaust, it is also important that the sub 1,500 rpm range not be as intense as it initially was. I am happy with that range as it is now because before it was hard to start rolling without it seeming like I was waking up the neighborhood (but of course this was really only inside the car -- outside wasn't bad).

https://lh4.googleusercontent.com/-j...to%2525204.JPG

https://lh5.googleusercontent.com/-W...to%2525203.JPG

https://lh4.googleusercontent.com/-0...to%2525202.JPG

https://lh5.googleusercontent.com/-B...to%2525201.JPG

Welding done by PiperMotorsport in Sterling, VA. It is excellent.


Measurements used:

https://lh5.googleusercontent.com/-5...282%252529.JPG
https://lh6.googleusercontent.com/-2...282%252529.JPG
https://lh5.googleusercontent.com/-p...282%252529.JPG
https://lh3.googleusercontent.com/-2...282%252529.JPG

So there is a lot of scientific material out there on how these resonators work. Basically, if you take a beer bottle and blow over the top, there is a sound created. Now fill the bottle with a little water (effectively shortening the pipe) and blow over the top and it is a higher pitch. OK, well that's great, but I need to know whether I want the higher pitch or lower pitch because it is not the sound, but the effect of the frequency cancelling out the sound that I don't want. That makes it seem to me that the lower sound is what I want (ie longer pipe). That would cancel the lower frequency drone that I am concerned about. But them I'm confused as to whether the longer pipe would raise the effective area within the rpm band or not.

I mean it would be easy to go one way and then see what the result is, but I would prefer to save money and time by guessing the proper way the first time.

Should of been an engineer...

Well I guess if someone was smart they would make a two piece Helmholtz resonator. One piece would slide into the other so it would be adjustable(length wise), that way you could try other lengths until you found the one that worked at the right rpms for your application. Then if it worked get a patent on it and take it to the market. Make a lot of money and go see the world. That's what I'd do but I'm not that smart. :ponder:

ROD
p.s. the welding does look excellent :tipwink:

How come your OEM helmholtz resonator on the stock exhaust looks different than mine? It is oval shape and 10cm longer?

Mine is smaller and more rounded, would you think the shape would make a difference?

I have a 2008 CR. If you have an AP1, it is probably the cylindrical type. Yes, and the replica is of similar shape and size, but slightly bigger. I think the fact that the new system is 70mm has more to do with the requirement for a longer/shorter length. OEM is 60mm