[QUOTE='10Anamoly;650399]I did this on my car, first with 22" side branches and had no luck. After re-doing my math and using some Audacity frequency analysis, I figured out that they had to be 27-28" to work at the RPM I wanted. Longer pipes tune out frequencies lower in the RPM range. Shorter pipes (increasingly less effective) hit the higher rpms. I had the mechanic fix the pipes to 28" and VOILA, absolutely zero drone from 2200rpms to 2800rpms. At 2000rpms there is a slight rumble in the cabin, but no drone. Same at 3000rpms which changes into an aggressive purr.QUOTE]

i just had mine done and i dont get a drone until 3900-4500 depending on gear and load. how would i figure out how long i would need to make my T branches?

i came up with 18" if the drone is at 4k rpms but if its going to 4500 should i shorten it?

For that RPM I believe that 18-19" would work. However, you can always fab up the elbow and the tube seperately, test a length of pipe, clamp it down and see if it worked. If not, trim the pipe down, reclamp and test, kind of like tuning a tuba. Then whatever works, weld it up permanently.

Great idea

Anamoly, first I just want to thank you for sharing this information, I have a similar issue on my custom exhaust for my 2010 Genesis Coupe 2.0t (currently 380whp)

I have a 3in turbo back exhaust going to a Summit Turbo Style Muffler with one 3in inlet and two 3in outlets, with two 2.5 pipes going to a quad tip exhaust for the 'fake' dual exhaust look (because our bumper has the dual cutouts anyways and it just looks better being symmetrical IMO)

Anyways.. I also have a drone from about 1800-2400rpm depening on speed/gear/etc. and no way of measuring the resonance, I'm hoping you could give me a rough ball park of pipe length/diameter to start tuning with, after reading this whole thread, I'm thinking maybe 36-40 would be a decent starting point, do you agree?
For the diameter, it looked like you were recommending 2.25 for guys with 2.5in exhaust, was that accurate?

Also, you said between the muffler and tips, for me that is about a 2ft distance front to rear, but nearly 3ft of actual piping due to bends, does it matter where along this area the pipes are fitted, will it make any difference at all?

And one last thought.. Does the pipe have to be capped, or could you simply weld a pipe connecting the L and R tips together, I'm sure I have seen a setup like that before, but I have no idea where or if this was it's intended purpose, but it seems like it might accomplish the same thing?

Thanks again!

I did this on my Tacoma to get rid of drone. I used the same diameter pipe as the tail pipe at 1/2 the length of the tail pipes capped on the ends.

http://i283.photobucket.com/albums/k...h/SDC10348.jpg

Worked great!

hmmmm nice>>

You would want one side branch per 2.5" exit pipe after the mufflers. The direction does not matter for the branches but the length and location do (anywhere after the final resonator or muffler is fine). I would use 36-40" to kill drone in that range. I would note though that you may eliminate 80% of the drone range but not all since this only affects a short frequency range. It should help plenty though. You can always test different lengths of pipe (make the welded elbow and then clamp on different extensions) to see which works best and then weld it permanently. They do have to be capped at the end of each branch too, no packing inside though. The diameter of the side branches should match the diameter of the primary exhaust pipes.

PS - nice numbers, what turbo did you swap in there?

Thanks for the advice and quick response, sorry about my own delay getting back to you.
I've done some more testing since reading about this and it's actually more in the 2-2400 range, so now I'm thinking 34 might be a closer match. I've also noticed a similar drone-type noise/vibration around 3500-4k which doesn't bother me as much since it's not a cruising range, but I was wondering if throwing a 12inch or so pipe might help eliminate that as well.

And to answer your other question, gt3071r, tuned with AEM fic.
It doesn't start spooling until about 35-4k with full boost just over 5k, it would be a lot of fun except my rev limit is still 6500ish (sometimes it slips over sometimes it doesn't *shrug*) so I don't get a lot of time to enjoy it, but it's also been under 40degrees the whole time I've had it, so maybe with the warmer weather it will behave better? Or I might just need a better tune.

I didn't want to clutter up your thread with too much information on my own car, so I just threw that number out there so it was understood that the car isn't stock. :p

Sounds nice bud. :)

I have some major drone between 1,800 and 3,000 rpm and have read over the whole thread to figure out the ideal length. I figure 29" would be ideal, but am not entirely sure. What length would you recommend Anamoly? Also, is that length the entire Helmholtz chamber from the exhaust pipe to the cap?

Also, since my entire mid pipe has no resonator (x pipe is resonated), would it also be effective to just weld in two resonators in the midpipe?

Standard resonators kill higher pitch rasp. Side branches tuned to 28-32" lengths kill low RPM drone (2k-2600k usually).

Thanks for the help Anamoly, the only problem is that the hangers for the rear muffler section on my new exhaust will get in the way of placing the branch resonators behind the two rear mufflers. If they are mounted before the mufflers HKS style, would they still be effective?


Edit: here are some pictures of my setup, where would you recommend mounting the branch resonators? Note the exhaust hangers are sort of in the way behind the mufflers.


http://i648.photobucket.com/albums/u...-02-061611.jpg
http://i648.photobucket.com/albums/u...-02-061612.jpg

Additional Information Regarding Branch Resonators
 

If anyone is feeling like a good read on how these helmholtz resonators work, I found a number of very interesting and insightful sites where people calculated the size of the resonator and the effects it had. All were positive, just to spoil the surprise!


Branch resonators - ways of reducing exhaust drone

Exhaust Drone is Completely Gone - Ford Mustang Forums : Corral.net Mustang Forum

Here’s the Lightest, Freest Flowing, Quietest Exhaust for the NSX - NSX Prime

hi may i know how u derived the final length of the resonator? may i know the formula?