etang789

I have played with the calculator more seems like if a larger Radius of side branch will make the Resonant graph wider. May be this is why they increased the OEM sidebranch size?

nlink720

Just replied to someone's PM, so I figured I would update this thread with the latest info I provided him:

"Hey [name removed],

I still have mine. The following is a list of my suggestions:

Step 1. If you can get one, start off with a 70mm Berk high flow cat. This is easy to install and reduces the drone. The car will still be loud, but not drone as much. Also, I noticed a large performance increase when I added the HFC to the Greddy Ti-C. If this is still too much drone, then go to step #2.

Step 2. If there is still too much drone, then take a piece of cardboard and put it around your OEM Helmholtz resonator and make a template. I used cardboard and tape and brought it to a quality welding shop and told them that the inner diameter of the cardboard template was to match the outer diameter of the Helmholtz resonator that they were to fabricate and weld onto my Greddy Ti-C exhaust. (I brought only the pertinent section of the Ti-C).

I measured and marked in a heavy duty black Sharpie the location for them to cut the opening and weld. I also included several pictures of the OEM exhaust so they would have a better idea of how it should be positioned.

*** MAKE SURE that you mark the Ti-C in a manner that will not cause the new Helmholtz resonator to angle upwards towards the top of the car because it will rub against the indent in the bottom of the car. If you look at the bottom of the car where the OEM Helmholtz is located you will see that there is a small indent in the underside of the car. This is the area where, if the the Helmholtz is angled improperly, you could have rubbing or inability to fit the Greddy. I did not have this problem, but mine was angled slightly upwards towards the top of the car, and I could see how it could happen.***

I am happy with mine -- it doesn't drone much at all, but is loud like a motorcycle when I get on it above about 6000 rpm. I really love it. It is not quiet at other times, but is bearable without the silencer.

Throw in the silencer and it is 100% as quiet as OEM.

Can't go wrong with the high flow cat and Helmholtz!!

Let me know if you have any more questions.

Good Luck!!"

Floppy

Compete thread resurrection here but I think this will solve all my problems with my buddy club prospec dual. Daunting all the same for me to consider cutting a hole in my nice, new exhaust system...

Mr-T

Another thread revival!!!

Floppy, did you ever do this?


Looking to do something to my Skunk2.

Any advice on lengths and sizes? The skunk2 is a 70mm tube, so thought I would add a 60mm branch, possibly same length as OEM. in same position as OEM.

Also, anyone know if the position along the pipe is key? Cant see any mention of it. Was thinking of instead of cutting into the exhaust itself, to add the resonator into the test pipe.
Will this completely change what is required size wise?

Finally, from all other forms I have read, the resonators all seem to be massively long! circa 25"+ some up to 35".
The OEM one is about 6". Why is it so much shorter?

Tmajima

Thread revival #2

I think it's a pretty good contribution though.

Shadoww

I actually did this mod and it really helps with drone.
My set up is test pipe + hks 75mm single and it was too loud for me.

As far as the position of it I put it as close as the headers as I can because the wavelength of sound depends on the temperature of the exhaust.
I think the EGT for the s2000 NA is about 800F, so I just assumed temperature was 800F for the hell of it.

We're looking to eliminate the drone at about 3400rpm. Another guy on this forum noted that the sound wave length was somewhere between 110-116hz. I calculated for 112hz. [that other guy is 'Reliable' btw]


After I mathed everything out... it came out to 2" piping thats juuust over 6.75" long (6.77).

So instead of cutting up my exhaust, I cut up a test pipe and welded that pipe in. It actually fits and sounds quite nice!

Mr-T

Good to see positive results.
Unfortunately I have not yet had a chance to get my Skunk2 modified, but will hopefully get it done over the next couple of months.
As I already have a spare Skunk2 mid section, I will follow the OEM direction and install the resonator in OEM position.

Will update once completed.

gptoyz

This is pretty awesome!

If you guys can, add some before and after sound recordings. Hopefully under near similar conditions. I think the worst drone occurs @ about 75 mph 6th gear, near flat slope - so minimal throttle angle.

Chuck S

Any of you college boy math majors got a spread sheet where the rest of us math idiots can plug in pipe inside diameters, lengths, alloys, etc., etc.?

-- Chuck

Tmajima

If someone can lend me a 70mm test pipe that's lives in CA we can do a before/after recording! (:
I'll record something for you guys in the meantime!

I made a simple excel calculator that will do piping size, so you can email me for it or just ask me and I can calculate it for you.

As far as what alloy to use I would stick with the same alloy that your exhaust was made out of. Usually it'll be 304 or 409.

andrewhake

I was thinking of doing something similar. I don't really have an issue with drone but 70mm exhausts seem to add a good amount of rasp around 5-6k rpm, would be interesting to see how the extra little helmholtz resonator could help with that.