My Magnaflow cat-backs had the 2000 rpm drone and was driving me crazy. I read some info over in the Corral forums and decided to try it. IT WORKS!!!
The problem is the engines strongest tone at 2000 rpm causes the tail pipes to resonate (vibrate like a pipe organ). The fix is to install Side Branch Resonators on the tail pipes to cancel the tone.
Here's the link to the Corral forum, it's explained in good detail there with pics.
My Magnaflow cat-backs had the 2000 rpm drone and was driving me crazy. I read some info over in the Corral forums and decided to try it. IT WORKS!!!
The problem is the engines strongest tone at 2000 rpm causes the tail pipes to resonate (vibrate like a pipe organ). The fix is to install Side Branch Resonators on the tail pipes to cancel the tone.
Here's the link to the Corral forum, it's explained in good detail there with pics.
Seems like you could achieve the exact same effect by moving the mufflers forward a few inches. That will lower the frequency at which it drones and use bigger pipe aft of the mufflers to give it a lower rumble. I love the way my car sounds at 2 grand, yeah it drones, but I like it. I may head to an exhaust shop sometime to see how much 3 inch pipe from the mufflers back would cost.
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Hi, my name is Eric, I am in Australia and I’m very interested in this remedy for exhaust drone.
In the spirit of honesty, I have to say I don't drive a Mustang. (Would love to get a 66 convertable one day), but I have just put a new 2.25” exhaust on my 1989, 4 door, 2 litre 6 cylinder Nissan Skyline.
It's no muscle car, but I'm happy to say it’s an improvement on standard, except for the drone.
The exhaust shop guy had no idea how to get rid of it, without fitting a big tri-flow muffler at the rear. He basically said he had no idea why it occurred, and that it's normal in a sports system.......
After a month of driving I’ve just had them change the tri-flow for a straight through muffler. So while he’s welding it on, he says the drone would be worse, and that he’d not be putting any other mufflers on for free because I asked for this specific one. I see his point and that’s fine.
Now it’s breathing a lot better and there’s even a hint of a good tone lurking too - but THE DRONE (from 2K to 2.5K) IS KILLING ME!
So I saw this thread and HAD to see if I can get some more info.
I would be stoked to hear from anyone who has added the resonators.
Has anyone Grahams email address??
My system has extractors, the catalytic converter, a glass packed straight through resonator, about 5 foot of pipe and finally the rear muffler.
I have been talking to friends and we concluded the branch should be half way along the 5 foot piece of pipe. We decided the length of the mufflers should be ignored, because they are not as acoustically reflective as the pipe.
Does anyone agree/disagree?
I was going to make the resonator 1/4 of the length of pipe and mount it in the centre.I got the PDF file and it seems to suggest only one frequency is affected. I think that the affected frequency has got to be the drone frequency if it's in the middle - yes????
Thanks a lot, really looking forward to a reply and/or Grahams email address, have a great day, isn’t the internet amazing????
Yeah, my Flows are nasty loud @ 2000RPM, especially with an O/R h-pipe. But I kinda like it. It's the buzzing inside the car from loose stuff that bothered me. Got that all fixed though.
I found this thread about fixing the drone around 2000 rpm. I have a 2008 v6 and had a dual exhaust conversion kit from Pypes put on. The resonance through the car is driving me nuts. Been thru the shop a few times, no luck. The fix I hear about seems to be for prior generation cars, I wonder if someone found a fix with the new generation with the mufflers at the rear of the car?
If this isn't fixable, I gotta go back to one pipe...
Welcome to AFM. We are glad to hear from all hot rodders. Maybe you'll get behind the wheel of a Falcon someday??
You can send a PM to Graham on Corral. I don't know if he still posts there, though.
For your anti-resonator, here's what I suggest: use a 2.5" dia. tube and slip it over the teed-in 2.25" dia. length. Use a 2.25/2.5 stepped band clamp to connect both tubes. This will allow you to slide the larger pipe back and forth until you get exactly the correct length to minimize drone. Once you get the right length, you can weld the joint if you don't like the clamp. If I was smarter, I could calculate the correct length. But, a little experimentation will save a lot of math and get the desired result!
HTH,
Chris
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Comp Cams XE268H's, PI intake (Livernois kit), MAC CAI, Accufab 75 mm TB & plenum, Steeda pulleys, SCT ProRacer tuning, Steeda springs, MM c/c, FRPP 3.73 gears, SVO girdle, Denny's Driveshafts 3" HD d/s, J-mod, FRPP trans cooler, VRS catted X, MagnaFlow exhaust, Hawk HPS pads, OEM Cobra headlights, fog & tail light re-wire, some other stuff…
OK, Graham's "resonance cancellation tubes" (RCT's) are installed in the tailpipes at the back (or was it the front?) of the gas tank. Graham found a nice space to tuck the two tubes up into but I can't remember if it was fore or aft of the tank. Take a look at the Corral thread for pics! Your dual exhaust will be the same as the original dual exhaust setup. It doesn't matter if the mufflers are at the back of the car or under the floor, it's the RCT's that will eliminate the resonance and they can go anywhere that is convenient.
They won't help as much but Bassani baffles slip into the 3.5" dia. MagnaFlow exhaust tips (9 or 10" long) and are held in place with a single bolt (each). These baffles have a 2.5" ID and will not hinder flow. More fiberglass insulation matte can be added to really quiet things down.
The last option is to use mufflers that are not straight-through design. Corsa makes some mufflers that are supposed to have "zero drone". I have not heard a Corsa muffler so I can't vouch for them but I haven't read any bad reports! Take it for what it's worth.
So, check out Graham's thread and you'll see the pics of the tubes. Your shop can fab up these things or, if you're handy, you can do it yourself.
Hey Chris;
Well, I picked up the car and it is all set! I found a set of GT exhaust mufflers and they bolted right on to the Pypes cat-back pipes and the sound is fantastic! I noticed on v6mustangstuff.com they sell this outfit. The car now has the perfect rumble, no v6 wheeze, no drone, and sounds great when you give her the gas. I highly recommend this as the best v6 system! I now have a set of Pypes mufflers for sale, would be perfect as a v8 upgrade! Thanks for all the help on this!
Sam
Exhaust Drone Is Fixed!!! 
