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Severe drone at 2.5k rpm after middle muffler delete.

spock345

Well-known member
Joined
Nov 3, 2016
Location
Livermore, CA
I replaced my middle muffler with a straight pipe after it fell apart on me due to rust. Now whenever the engine hits 2.5k rpm I get a really bad drone. I rather like the difference in sound most of the time but need to find some way to at least reduce the drone as I will be driving cross country soon and I think this will drive me insane. Is there an inexpensive way to reduce the drone?
 
Higher speed/higher rpm will get rid of the drone.

I would do that but the drone happens at 2500 rpm, which is where my automatic transmission likes to live while cruising at 60-65 mph. If I go below that or above 3000 the drone lessens or disappears.

I am just curious if there is a modification I can perform to the exhaust that will cost less than a $40 resonator.
 
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24.95 at amazon, and also good for working with tools.

40$ is a cheap fix, engineered by Volvo engineers, you aren't going to get better for cheaper.
 
Google "? wave resonator". It's basically a tuned length of pipe attached at 90? to the exhaust pipe.
 
What type of rear muffler is being run?

The stock rear muffler. I am intrigued by the 1/4 wave resonator. Might as well try that. I wonder if changing the weight distribution of the exhaust at all would change the resonant frequency?
 
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I?m also looking forward to the first test drive (actual troubles to get the car running normal after 1 year standing and wasted spark modification).
The resonators are quite heavy. Got them new for 10 Euro so no tragedy if they are useless...
 
Exhaust weights for drone/harmonic issues are quite common. I have the same condition as the OP at 2300, but it doesn't occur enough for me to have addressed it, so I can't speak for personal results. If I were going to try to remediate it, however, it's the only approach I'd take. Otherwise, I'd say F it.
 
1/4 wave resonators work, and work well. However, there's some science involved. If you decide to make one, make it adjustable so you can tune it appropriately. I can promise you won't get it right on the first try. Pipe diameter and length are crucial.

Or just buy a vibrant ultra quiet resonator and be done with it.
 
honestly, I'd ditch the rear muffler and put the resonator back on there. aside from the weight it's not a very restrictive piece.. and I doubt OP is at a point where a couple of lbs makes any difference whatsoever in the performance of the vehicle.
 
Remove all of your exhaust and just make a series of 1/4 wave resonators, so it looks like a pipe organ down there....you'll eliminate all the frequencies.
 
Thank you all for the input. This is definitely enough to keep me busy for a while. I will just have to start experimenting with my exhaust setup. Perhaps try experimenting with a few weights on the exhaust or the vibration absorbers to see what that does, then a 1/4 wave resonator if the previous approach doesn't work (I can actually leverage those college physics classes now). If all else fails I will experiment with mufflers, although I would rather not as I like the sound my exhaust makes right now, other than the drone.
 
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