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I have the same "technology" built into my custom Unobtanium exhaust on my RUF. Wouldn't have it any other way. Outside the car it sounds like a Cup car... inside no drone and completely liveable. There is actually quite a bit of science into "helmholtz resonators" which basically the pipes isolate and reflect certain frequencies to cancel out drone almost like noise cancelling headphones.
Every exhaust I do going forward will have the same stuff. Get to have my cake and eat it too!
Sick exhaust. Would love to hear the video. Are those cats welded onto that exhaust or the hemholtz resonators?
I do have one question. Was there a reason you picked 27 inches? If you go longer does it lessen the drone? From what I've read I believe I will be going with a 2 inch or larger diameter tubing.
The length is based off a calculation. The formula is readily available on line. The diameter can vary and the closer it's matched to your piping the greater the range is covered from what I've gathered.
Sick exhaust. Would love to hear the video. Are those cats welded onto that exhaust or the hemholtz resonators?
Cats in the back and you can see the drone pipes coming together in the middle where it is bridged with the unobtanium sheild in the middle between both drone pipes.
Some sound clips from similar systems (but not my car):
I do have one question. Was there a reason you picked 27 inches? If you go longer does it lessen the drone? From what I've read I believe I will be going with a 2 inch or larger diameter tubing.
What FFM said above. I calculated the length to negate a drone caused by a wavelength that occurs at 1,850 rpm (don't recall the specific hz of the wavelength off-hand). The drone range for my exhaust was about 1,500 rpm to 2,250 rpm, so I aimed for a wavelength of a drone created at 1,850 rpm and hoped that it would be be most effective there, but also capture most (or all) of my drone range as it's effectiveness tapered off in each direction. As far as my ears can tell, it seems pretty equally effective over the entire drone range. The longer the resonator the lower in the rpm range it is effective. Some guys have built adjustable resonators - think trombone slide - so they can dial in the effective rpm range before welding up a final length. I've read that you can attempt to reduce peak effectiveness of the resonator but widen its effectiveness over a larger rpm range by adding sound resistance (ex. via steel wool stuffed into the middle of the resonator), but I didn't do this, so I can't add any experience to that theory.
Diameter of the resonator affects the total attenuation (volume reduction) of the resonator. So since I used a 1.75" resonator an a 2.5" exhaust pipe, my total volume drop caused by the resonator was somewhat less than I could have achieved by a larger diameter resonator.
Interesting. My drone still sucks after adding a resonator. I have the DES & ISS headers
Btw where would you run the 2" piping?
Bummer. I assume you added the side branch (not inline) resonators. Where did you add them, and what diameter and length did you use? Did you get any drone reduction at all in any part of the drone range? Interested to hear more details of your setup and results. My 1.75" diameter, 27" long resonators did not eliminate my drone, but it reduced it below the obnoxious level, and it is now fine for my purposes.
As far as where 2" piping would fit: I think it MIGHT fit if you tee'd into the exhaust behind the v-band clamps (near the rear axle), aimed toward the outside of the car on each side, and then curved toward the back of the car following each exhaust pipe back to the mufflers, and then curve and follow along the front and then side (the side closer to the outside of the car) of each muffler. It may be tight enough that you'd have to tack each resonator to the muffler itself, but I don't think that would cause any issues, and would secure the resonators from rattling on the mufflers. Maybe you could even squeeze 2.25" pipes in that space if you have a really good fabricator? Not sure of the 2.25" pipes - I haven't measured for that - just trying to brainstorm here...
Bummer. I assume you added the side branch (not inline) resonators. Where did you add them, and what diameter and length did you use? Did you get any drone reduction at all in any part of the drone range? Interested to hear more details of your setup and results. My 1.75" diameter, 27" long resonators did not eliminate my drone, but it reduced it below the obnoxious level, and it is now fine for my purposes.
As far as where 2" piping would fit: I think it MIGHT fit if you tee'd into the exhaust behind the v-band clamps (near the rear axle), aimed toward the outside of the car on each side, and then curved toward the back of the car following each exhaust pipe back to the mufflers, and then curve and follow along the front and then side (the side closer to the outside of the car) of each muffler. It may be tight enough that you'd have to tack each resonator to the muffler itself, but I don't think that would cause any issues, and would secure the resonators from rattling on the mufflers. Maybe you could even squeeze 2.25" pipes in that space if you have a really good fabricator? Not sure of the 2.25" pipes - I haven't measured for that - just trying to brainstorm here...
Sorry for the confusion & late reply. I haven't tried your route. I cut out my x pipe merger and and put in a resonated 2 to 2 magna flow. It tamed meh exhaust tone down a few but did NOTHING for the drone
I wanna try your route or..
try those helmholtz pipes. Not sure where to get em though. I saw a company sell the nice L shaped helmholtz pipes but I can't find them any more
I had my side branch resonators custom made by a local exhaust shop. They don't really need to be mandrel bent. But if you have the ISS Forged DES exhaust try something else to kill the drone first. I'm on my phone, so can't link to it, but search on here for the thread titled "Borla drone reduction in 20 minutes for $20" or something like that. I posted results for the DES exhaust with that method in that thread. Adding the silencers referenced in that thread did more to reduce my drone than the side branch resonators. And was much easier & cheaper.
Revival thread. Thanks OP for the calculations. 2" diameter 27" length approximations.
My final set up is PPE UEL > (2) gesi 10025 cats > dual in/dual out spintech 3000 xlp > (2) ~27" length 2" diameter quarterwave length resonators. My overall piping is 2.5" hacked up Xforce catback.
I have "bazooka" pipes so I had mine routed along side them giving me the most space, clearance, and ease of access to my bolts.
Exterior noise outside maybe decreased by around 20% but the kicker is interior noise/drone reduced by over 75%. Night a day difference. The drone use to buzz my "oh fecal! handles" with great ferocity and caused all sorts of mystery rattles/buzzing inside the car during the DRONE BOMB of ~1800-2300~ common ISF range. At the boomiest of the range my teeth and skull would actual create a buzzing harmonic, good riddance to that bull... So far no more buzzing/rattling but it was warm today overall which even previously helped reduce some buzzing/rattling.
If I recall correctly, I'm thinking it might be quieter than when it was xforce catback ONLY but the sound is easily 3x louder than with xforce catback only.
01-15-17, 06:58 PM
