Exhaust Drone Fix
06-22-2009, 09:26 PM
#61
I am no engineer or mathematician, but I really think that if you increase the volume of the branch resonator (up the pipe diameter) that it would assist in reducing drone at the selected RPM with a slightly shorter pipe. I feel like it would essentially allow the sound wave to stabilize and get out of phase faster in the resonator. However my understanding of frequency might be a little bit off.
Also, TS77, is there a way to graph the movement of the drone (through the RPM band) in proportion to exhaust speed? If the movement of the drone is a constant, then an adjustable resonator can be constructed using slight spring pressure to moderate the length of the pipe. Something like a Power Valve on a Rotax Kart Engine (which is a vaccuum operated {vaccuum in the exhaust system}, spring pressure regulated valve to control exhaust flow...it enables you to move the power band around) What do you think?
Also, TS77, is there a way to graph the movement of the drone (through the RPM band) in proportion to exhaust speed? If the movement of the drone is a constant, then an adjustable resonator can be constructed using slight spring pressure to moderate the length of the pipe. Something like a Power Valve on a Rotax Kart Engine (which is a vaccuum operated {vaccuum in the exhaust system}, spring pressure regulated valve to control exhaust flow...it enables you to move the power band around) What do you think?
Last edited by 03 BLACKOUTSSS; 06-22-2009 at 09:34 PM.
06-22-2009, 10:25 PM
#62
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Ya BlackoutSSS, you're pretty close to it. Increasing the tubing diameter will change the amplitude of the standing wave formed in the closed pipe which will give you more destructive interference (better resonance cancelling). Changing the length of the pipe changes the frequency the closed pipe produces so the trick is to match the match the loudest drone zone in the RPM range with the correct length closed pipe.
I have no clue how to graph the drone through the RPM range vs. exhaust speed. Im sure if you really wanted to, its possible, but I think the benefits would be minimal. There's only so much you can do with a branch resonator I would think. It would take a lot of time tuning the thing to work and I dont think it would be worth the time trying.
But i do agree, you have a great idea. You could put a linear actuator or step motor and make it to where you can remotely adjust the length of the pipe. Hell, take it a step further linking it to what you said, you could program it to where it adjusts the length of the pipe with respect to the RPM so you can always have the best resonance reduction while you're driving... Its just a balance of time, money, practicality, and other things. Better off just getting a quieter muffler.
I have no clue how to graph the drone through the RPM range vs. exhaust speed. Im sure if you really wanted to, its possible, but I think the benefits would be minimal. There's only so much you can do with a branch resonator I would think. It would take a lot of time tuning the thing to work and I dont think it would be worth the time trying.
But i do agree, you have a great idea. You could put a linear actuator or step motor and make it to where you can remotely adjust the length of the pipe. Hell, take it a step further linking it to what you said, you could program it to where it adjusts the length of the pipe with respect to the RPM so you can always have the best resonance reduction while you're driving... Its just a balance of time, money, practicality, and other things. Better off just getting a quieter muffler.
06-22-2009, 10:53 PM
#63
This is pretty interesting stuff. I have a magnaflow 13740 which has a 36" case and I didnt have any drone when I didnt have cats, but when I put 2 high-flow magnaflow cats on it now drones around 2000rpm which is very fustrating since cats were suppose to quiet it down.
06-24-2009, 11:42 AM
#67
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OK, I gotta add my 2 cents here. The side branch resonator works.
I did the side branch resonator on my 08 Silverado about 6 months ago. After putting on a Magnaflow cat back with a single 3" tailpipe, I had a drone at 1600-1700 rpm. I had read about eliminating drone on the Mustang forum and found the resonance calculator linked back in post #24, so I figured it was worth a shot. I made my resonator from 2 1/4" OD pipe, 2 1/4" ID flex and some hose clamps. Total cost using aluminized pipe was probably $15.
The calculator told me I needed to add about 30" to move the drone to 4000 rpm, so I made it to be adjustable between 24" and 36". Turned out that 30" was perfect. The drone was completely gone, not just moved up to 4000 rpm.
I made a 1"x2" hole in the tailpipe right after it goes over the axle, clamped a T to it, and ran the resonator crossways under the bed. I've since redone the original experimental setup with stainless pipe and Torca clamps, but the design remains the same.
My T is at 90° to the tailpipe, but I doubt that it matters.
I did the side branch resonator on my 08 Silverado about 6 months ago. After putting on a Magnaflow cat back with a single 3" tailpipe, I had a drone at 1600-1700 rpm. I had read about eliminating drone on the Mustang forum and found the resonance calculator linked back in post #24, so I figured it was worth a shot. I made my resonator from 2 1/4" OD pipe, 2 1/4" ID flex and some hose clamps. Total cost using aluminized pipe was probably $15.
The calculator told me I needed to add about 30" to move the drone to 4000 rpm, so I made it to be adjustable between 24" and 36". Turned out that 30" was perfect. The drone was completely gone, not just moved up to 4000 rpm.
I made a 1"x2" hole in the tailpipe right after it goes over the axle, clamped a T to it, and ran the resonator crossways under the bed. I've since redone the original experimental setup with stainless pipe and Torca clamps, but the design remains the same.
My T is at 90° to the tailpipe, but I doubt that it matters.
06-24-2009, 07:17 PM
#68
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Murphdog, when you say "the calculator linked back in post #24" are you talking about on this thread or on the mustang forum? Did you use this calculator?Auto Lounge Calculator
Im trying to come up with how you did your math. Maybe you could explain it to me.
Thunder550, sounds like 35" would be too long. The graph you looked at is probably off by a little. Maybe Murphdog can clear up the math, but it seems like between 30-32" would be closer to the correct length.
Im trying to come up with how you did your math. Maybe you could explain it to me.
Thunder550, sounds like 35" would be too long. The graph you looked at is probably off by a little. Maybe Murphdog can clear up the math, but it seems like between 30-32" would be closer to the correct length.
06-25-2009, 09:06 PM
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Yeah, I was referring to your post #24 on this forum...the autolounge.net calculator. I originally had found the calculator from reading the Mustang forum 6 months ago.
I plugged 1700 into current resonating rpm, 4000 into desired resonating rpm and 8 into cylinders per pipe ( since I have single exhaust) and it told me to add/remove 2.79 feet. I added 2.5 feet and it worked perfectly. I'm not sure how it works if you have 2 tailpipes instead of one. If you put 4 cylinders per pipe into the calculator, it comes up with twice the length to add/remove. I'd guess you would have to add half the calculated length to each side, but I don't know. I remember seeing some pictures on that Mustang forum where they were putting resonators on each tailpipe and running them crossways back of the rear axle.
Anyway, there's a lot of math behind this acoustical resonance stuff and I read up on it til my head hurt. I couldn't find a sure fire way to calculate the needed length until I found the autolounge calculator.
I'm very happy with the way it worked for me, no resonance at any rpm. Here's some pics of my first attempt with cheap aluminized pipe and hose clamps.
I plugged 1700 into current resonating rpm, 4000 into desired resonating rpm and 8 into cylinders per pipe ( since I have single exhaust) and it told me to add/remove 2.79 feet. I added 2.5 feet and it worked perfectly. I'm not sure how it works if you have 2 tailpipes instead of one. If you put 4 cylinders per pipe into the calculator, it comes up with twice the length to add/remove. I'd guess you would have to add half the calculated length to each side, but I don't know. I remember seeing some pictures on that Mustang forum where they were putting resonators on each tailpipe and running them crossways back of the rear axle.
Anyway, there's a lot of math behind this acoustical resonance stuff and I read up on it til my head hurt. I couldn't find a sure fire way to calculate the needed length until I found the autolounge calculator.
I'm very happy with the way it worked for me, no resonance at any rpm. Here's some pics of my first attempt with cheap aluminized pipe and hose clamps.
06-25-2009, 10:38 PM
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Ya I tried reading everything I could on the math behind it, I even broke out the old physics formula's.
You know, I was looking on that calculator, if you take the "Current Standing Wavelength" (inputed your 1700 RPM) which is 4.85 feet and devide that by 2 gives 2.425 feet which is closer to the length of 2.5 feet which you used.. I wonder if they're related.
I wish I had the time and money to research this a little more and figure out the math behind it because it is a really simple fix. Thanks for your input Murphdog.
You know, I was looking on that calculator, if you take the "Current Standing Wavelength" (inputed your 1700 RPM) which is 4.85 feet and devide that by 2 gives 2.425 feet which is closer to the length of 2.5 feet which you used.. I wonder if they're related.
I wish I had the time and money to research this a little more and figure out the math behind it because it is a really simple fix. Thanks for your input Murphdog.