Exhaust Drone Fix
Sep 1, 2008 | 12:09 AM
#1
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From: nor-cal
Exhaust Drone Fix
My friend ended up getting a flowmaster 50 series delta flowmaster and it sounded pretty good on his jeep but he hated it on the freeway because of the resonance. He did some searching and found this link. If anyone is big into technical stuff, you should look into it if you have a resonance problem. Taking physics, we knew about some acoustics and so we did the numbers and it all makes sense.
Here is the link. Its pretty intense stuff. No more drone
I'll ask my friend to take a picture to upload since there arent any good ones on that site. Our install looks pretty clean. But you would scratch your head if you didnt know what it was, cuz it seems wrong to do it.
When we did it, there was a huge decrease in resonance inside. There is some left but you really have to listen for it and have a load on the engine.
Here is the link. Its pretty intense stuff. No more drone
I'll ask my friend to take a picture to upload since there arent any good ones on that site. Our install looks pretty clean. But you would scratch your head if you didnt know what it was, cuz it seems wrong to do it.
When we did it, there was a huge decrease in resonance inside. There is some left but you really have to listen for it and have a load on the engine.
Sep 4, 2008 | 12:59 AM
#6
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From: nor-cal
Here are those pics. Sorry it took longer. I drew a little thing on paint if you cant make it out from the pictures.
Basically what this does is similar to blowing over the top of a coke bottle. The frequency that this pipe (coke bottle) produces matches the frequency that the exhaust resonates the worst (1900 rpm) and is a quarter of a wavelength out of phase with the exhaust so there is a canceling effect thus reducing the drone heard inside the car.
Basically what this does is similar to blowing over the top of a coke bottle. The frequency that this pipe (coke bottle) produces matches the frequency that the exhaust resonates the worst (1900 rpm) and is a quarter of a wavelength out of phase with the exhaust so there is a canceling effect thus reducing the drone heard inside the car.
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Sep 4, 2008 | 01:03 PM
#9
Quote from the link:
Seems like it would be a lot like the factory intake tubing. I'll see if I can find a pic of what I'm talking about, but I remember there being a little turkey gobbler looking thing hanging off, and wondering WTF it was. Must have been a resonance chamber or whatever it's called.
My magnaflow had the usual 2000 rpm drone, so I tried something a little different (I think) to get rid of it. The drone is now not just better, it is completely gone - the exhaust is downright quiet cruising at 2000 rpm. I read an article on the internet about "tailpipe resonance", and decided that this has to be the problem with aftermarket catbacks. They probably all have the same 6ft tailpipe mine has, which if the exhaust is at about 500 degrees, will resonate at 134 Hertz, which is the engine firing rate at 2000RPM. So I added a 134 Hz, 1/4 wave resonator to both tailpipes. Its just a section of pipe "T"ed into the tailpipes right in front of the gas tank. They are about 26" long each, which maybe a little shorter than ideal, but that's what fits in the available space. 26" must be long enough, because it sure as heck works. One end of each pipe is welded shut, and the other is T'ed into the tailpipes. If anyone is interested, I can try and post a picture.
