Help with exhaust resonance
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Junior Member
Joined: May 2004
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Help with exhaust resonance
I hope you can give me some advice or help! I am a Dodge truck owner (I'm willing to accept some flack because of that!), and have been unable to resolve this problem. I've posted my question on Dodge Truck World, and while there's been some good ideas, nothing has worked. Here's what's going on:
Truck: 2004 Dodge 5.7 Hemi. Mufflers: Had a Magnaflow 14579 SISO installed with stock 3" piping retained. Huge resonance between 1600 - 2000 rpms. Removed that, had a Magnaflow 14256 SISO installed. Same resonance. Removed that, had a Magnaflow 14588 SIDO installed, using dual 2.25" outlet pipes. Same resonance as with first 2 mufflers.
Like many of you, I went with the Magnaflow over Flowmaster because its packed design is less prone to boom or generate resonance inside the cab. Magnaflow recommended each successive muffler to reduce or eliminate resonance, but it hasn't really made any difference. Each muffler install was done by a Magnaflow shop, and no part of the exhaust was touching the frame or any other body parts. All factory hangers and rubber isolators are used, and the system is sitting in a "neutral" manner (not pulled to one side or the other). All connections are welded (checked top of welds with mirror) with no visible or audible leaks.
Things I've tried with no change in resonance: 1) Clamping all parts of the exhaust system and muffler with heavy 2" angle iron (used hose clamps and C and D clamps), no difference. 2) Wrapping heavy steel cable around the pipe and muffler, as well as wrapping heavy angle iron against muffler, then pulling it tightly against the frame with a turnbuckle. No difference. These 2 mods were an attempt to increase the mass of the system and change the resonant frequency, but made virtually no difference.
I'm at a loss for what to do next. The resonance booms inside the cab, and is very loud. I've considered Dynomat or other sound deadening materials to line the inside of the cab with, but there has to be something that can be done to the exhaust to reduce or eliminate the source of the resonance. I know that the F150 used to have one or two counterweights clamped to the exhaust -- do you think this is worth a try?
I'm open to any and all ideas you may have. Thanks for helping out a Dodge brother.
Truck: 2004 Dodge 5.7 Hemi. Mufflers: Had a Magnaflow 14579 SISO installed with stock 3" piping retained. Huge resonance between 1600 - 2000 rpms. Removed that, had a Magnaflow 14256 SISO installed. Same resonance. Removed that, had a Magnaflow 14588 SIDO installed, using dual 2.25" outlet pipes. Same resonance as with first 2 mufflers.
Like many of you, I went with the Magnaflow over Flowmaster because its packed design is less prone to boom or generate resonance inside the cab. Magnaflow recommended each successive muffler to reduce or eliminate resonance, but it hasn't really made any difference. Each muffler install was done by a Magnaflow shop, and no part of the exhaust was touching the frame or any other body parts. All factory hangers and rubber isolators are used, and the system is sitting in a "neutral" manner (not pulled to one side or the other). All connections are welded (checked top of welds with mirror) with no visible or audible leaks.
Things I've tried with no change in resonance: 1) Clamping all parts of the exhaust system and muffler with heavy 2" angle iron (used hose clamps and C and D clamps), no difference. 2) Wrapping heavy steel cable around the pipe and muffler, as well as wrapping heavy angle iron against muffler, then pulling it tightly against the frame with a turnbuckle. No difference. These 2 mods were an attempt to increase the mass of the system and change the resonant frequency, but made virtually no difference.
I'm at a loss for what to do next. The resonance booms inside the cab, and is very loud. I've considered Dynomat or other sound deadening materials to line the inside of the cab with, but there has to be something that can be done to the exhaust to reduce or eliminate the source of the resonance. I know that the F150 used to have one or two counterweights clamped to the exhaust -- do you think this is worth a try?
I'm open to any and all ideas you may have. Thanks for helping out a Dodge brother.
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Junior Member
Joined: May 2004
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One last appeal for help...
It's probably unconventional for a Dodge guy to ask for help on a Ford forum, but we have trucks in common, and a lot of expertise on the forums. I would be very grateful for any ideas or advice you can offer me. Thanks.
It's probably unconventional for a Dodge guy to ask for help on a Ford forum, but we have trucks in common, and a lot of expertise on the forums. I would be very grateful for any ideas or advice you can offer me. Thanks.
just joking, sorry i can't help you, but hopefully someone will take the time to set you straight.
Senior Member
Joined: Mar 2001
Posts: 4,506
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From: Puyallup, WA
Is the resonance you are hearing a vibration or just the exhaust tone itself??
Doesn't the stock exhaust utilize a resonator? If it does and you removed it for your custom exhaust, that might be the cause... I thought the stock exhaust on the new Dodges had a pretty healthy tone to them already.
It's true that the Fords use a counter weight attached to the exhaust system to keep it from vibrating too much. My truck did not have one and I don't have a resonance issue, so I'm probably not the best source for ya after all.....
Good luck!
Doesn't the stock exhaust utilize a resonator? If it does and you removed it for your custom exhaust, that might be the cause... I thought the stock exhaust on the new Dodges had a pretty healthy tone to them already.
It's true that the Fords use a counter weight attached to the exhaust system to keep it from vibrating too much. My truck did not have one and I don't have a resonance issue, so I'm probably not the best source for ya after all.....
Good luck!
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Junior Member
Joined: May 2004
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Thanks for the feedback. The resonance is an extremely loud "boom" inside the cab, and is separate from the exhaust tone itself. I suppose it's a product of the exhaust gas velocity inside the pipe and muffler system, vibrating in synch with what sounds like the natural, resonant frequency of the truck or cab. It only occurs in the 1600 - 2200 rpm range when the engine is under load, and cannot be duplicated in neutral or park (or by power-braking).
The stock 04 Hemis do have a factory resonator, but there's no room to reinstall it in my system (SIDO) except before the muffler. I don't think it would help with the resonance in this location, and would probably reduce the overall tone of the muffler system... but may be worth a try. I'm at my wit's end as to what to try next, and it's so darn loud that it makes driving the thing unbearable. The 03 models did not have this tendency at all. The 04s added dual cats and the resonator, and I suspect there may have also been som engine management changes in the PCM. The stock exhaust note between the 03 and 04 models is distinctly different.
Thanks again for the feedback.
The stock 04 Hemis do have a factory resonator, but there's no room to reinstall it in my system (SIDO) except before the muffler. I don't think it would help with the resonance in this location, and would probably reduce the overall tone of the muffler system... but may be worth a try. I'm at my wit's end as to what to try next, and it's so darn loud that it makes driving the thing unbearable. The 03 models did not have this tendency at all. The 04s added dual cats and the resonator, and I suspect there may have also been som engine management changes in the PCM. The stock exhaust note between the 03 and 04 models is distinctly different.
Thanks again for the feedback.