has anyone pinged Tony from FI on this, be interesting to see what his take is?
what kind of power loss would you get if doing this, and im sure it also impacts your warranty

The resonator pipes are back by the tips and meet the exhaust at 90 degrees. As they are capped and are perpendicular to exhaust flow, there is no power loss.

I know this because I had the same exhaust before and after the pipes and have noticed absolutely zero loss with them off, just much more comfort due to the reduced drone.

Just to clear I dont have to make any hole in the FI exhaust or have to make hole where these new pipes will connect

WOT burns? black on ur bumper?????? :shakes head:

Yes, you have to use a hole saw to open up a 2" to 2.25" hole on the FI exhaust. That is where the sound waves travel through, down the resonator pipe, and back to cancel out the droning frequencies.

It's a trade off, keep the drone and dont touch the pretty exhaust or mod the exhaust and enjoy the silence (lack of drone, depeche mode style).

Wish I knew about this when I had b&b bullets on my C6. Wife would plug her ears with her fingers for the week I had it. Plus rep!

Im big Depeche mode fan :happydance: .... just trying to prepare myself to get this done as need it badly, lets see if someone with FI exhausts wants to do before me

Man when you posted this thread car was in workshop and I have been calculating this drone on rpm range...the vibration starts at 2100 and is there till 2800 depends on the gear and speed as sometime it dies on 2700. Its more if you stay in single gear and accelerate slowly all the way till 3000, but if you push the pedal hard then its a bit less.

So can you throw some light according to your calculations as I have no means to measure those frequencies.

For the pipes does those be in SS or normal exhaust pipe will do the trick. I am about to pull the trigger:confused: by making hole in FI exhausts

Since the FI setup is the same pretty much as mine and the drone in is the same range, I would use 28-30" pipes, one per side. Any shorter and it will tune out drone above 3000rpms where you dont have the problem. Regular steel is fine but I would use some hi-temp paint to keep it from rusting ever.

Thanks will plan the operation then :)

how do you measure like someone would need 28" or 30" or less?

Speed of sound (typically 1100ft/sec, divided by the frequency at which drone occurs, divided by four because you want it to reflect at 1/4 the drone wavelength to cancel it out).

So for drone around 110hz-112hz (around my setup), you get to 2.5 to 2.4 ft, or 29-30".

So fast intentions CBE drones.... I had no idea. Glad I didn't buy it last week.

But this exhaust doesn't
http://www.the370z.com/intake-exhaus...w-db-test.html

We need to confirm with Tony of f.I and let's see what his advice. I believe Tony tried a Lot of things before he decided to make his cbe. So give him a shot and wait for his respond. That's just only my own idea. :tiphat:

Might want to check the Fast Intentions thread before making a conclusion. I get mine this week and should have a full review soon, then again there are already over a 100 reviews of the exhaust. :p

:iagree: with thedreamer. And take a look how many sets Tony sell out. I'm one of his customer still waiting for his cbe. And didn't hear anything like drone or whatever negative from other forum member. So let's wait from thedreamer. Hey bro keep us updated. Whenever u got yours and installed. Let me know so I can meet up with u. I want to hear from it and see how's good is it. :happydance:

wow, shameless plug much? :ugh2:

So...to get the frequencies of your droning, you put a microphone to your exhaust and ran it through a spectrum analyzer (i.e. Audacity if you're not in a lab...haha) to get the peak frequencies? Out of curiosity, did you run any filters on the output, or was it all raw? How clean was the data?

Nothing serious, just piqued my curiosity. I like reading stuff like this.

:nutswinger:

Running FI exhausts for few months now, I can say the exhaust sounds awesome but what OP was referring to was not the normal drone (I can live with that) but vibration because of it. I do face that if I accelerate the car slowly(normal crusing) not pushing it hard as rpms has to go steady from 2k to 3k and its there for good 500 - 700, mine starts from 2200 and lasts till 2800.

This thread shouldn't be taken anything against FI as they are an awesome company with awesome product, its just people have their own preferences. My daughter(7yrs) hates this drone and avoid sitting in the car LOL. I went through doing a DYNAMAT sound proofing when upgrading the audio it has reduced this vibration (not talking about drone/sound/noise) but its still there and if Tony gives some input on this thread I am willing to do this DIY

Will this only work after the muffler? I have a single exhaust on my 350 and there really is no way of doing this after the muffler.

side note: not to go too far off topic will HFC's cause more drone?

[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?

What some of the guys are mentioning here is the incorporation of the quarter length pipe.

Length of pipe needed = Speed of sound / (4*/Frequency)

*4 is the factor for the quarter length

What some of the guys are mentioning here is the incorporation of the quarter length pipe.

Length of pipe needed = Speed of sound / (4*/Frequency)

*4 is the factor for the quarter length

Typically, 28-30" of length for each pipe will kill a lot of drone from 2300-2900rpms. Mine are 28".

And I thought a banana in the tail pipe cured all exhaust woes.

Hello! Not to hijack a thread but...I searched google to fix drone in my Z32TT and somehow found this thread.

My setup is 3'' dp and 3''->2.5'' tp with 2.5'' Greddy SP exhaust. My butt-dyno is saying I gained about 30whp but I do have annoying drone at 2300rpm-2900rpm lol. I have to speed up to 75+ mph to quiet down drone.

Since exhaust diameter is different which diameter should I use for my setup? 2.5'' or 3''? Based on what I've read 28-30'' capped pipe sounds about right? Thanks in advance!