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Low frequency exhaust drone

  #1  
Old 05-31-2013, 06:50 PM
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Default Low frequency exhaust drone

Ive investigated and asked about this in the past but since we are down to one car I gotta get my car to be a bit more conservative. Right now i love the stock exhaust look. And it has an aggressive sound, but I hate flowmaster. I see why its mostly for trucks and muscle cars. The muffler packs a punch at low frequencies. But my car cruises at low frequencies. I have a glasspack at 18" but its not long enough.

Its all about experimenting and learning through experience. And no I wont go back to stock just yet shipo :P

I did the math, its about 45hz the car drones at on the highway. I would need a six foot resonator to cancel that out... could a 3 foot make a difference then?

Im thinking about cutting the muffler off- or getting a new segment of exhaust piping and need some help finding something a bit better. Im thinking straight trough packed muffler type resonator as long as I can get it.

Any suggestions? I think I will test how it sounds with just the glasspack alone too.

Thanks
 
  #2  
Old 05-31-2013, 10:51 PM
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I did the math wrong. Two pulses per second... thats 90hz

with a 1/4 resonator I can cancel out cruise speeds at 3.125 feet. still a little long.

Anyone have luck with branch resonators?
 
  #3  
Old 06-01-2013, 08:36 AM
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how did you calculate 90hz from 2 pulses per second?
I'm not trying to be annoying i just don't understand your math
 
  #4  
Old 06-01-2013, 02:13 PM
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I know :P

I looked a lot into theis the past few days and am kicking myself cuz I didnt find this when I put my flowmaster on.

The engine opens the exhaust valves two times per revolution in a four cylinder engine. 2*(engine RPM) and then divided by 60 to make it revolutions per second. At 2700rpm I want to start to cancel the drone.

(2*2700)/60=90
hz just being the wave length per second.
 
  #5  
Old 06-02-2013, 03:21 PM
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two times per revolution. That's what I was confused about. Well, at that frequency you're losing the sub-bass frequencies in your music and that just sounds annoying. Attenuating that is a bit beyond my knowledge level. I'd say go for a branch resonator because of this.
My car has a similar problem, the piping is not standard and in a pretty awful state of modification. it steps from 2.5-3" down to 2.25", then to a factory muffler (the poor welding on it has now rusted through and the muffler is no longer on the car) and the drone is obnoxious in all steady-state driving. I deal with it though, since my budget is currently nothing.
EDIT:
 
Attached Thumbnails Low frequency exhaust drone-resonantpipes.jpg  

Last edited by kayweb; 06-02-2013 at 03:29 PM.
  #6  
Old 06-02-2013, 09:04 PM
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Thats how many times my the engine opens the exhaust valves per revolution right?

This is my final attempt since I dont wanna go back to stock yet. It shouldnt be too expensive to put this together. I just need to find the materials. Its harder than it seems. Especially capping off the end.

Ive read that it is suggested to put it on the tailpipe after the muffler. Like shown in the drawing. I have two tailpipes that dont go out very far. I think I can go before since I also have a glasspack near the cat.
 

Last edited by RobinsonRicer; 06-02-2013 at 09:07 PM.
  #7  
Old 06-02-2013, 09:49 PM
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Threaded piping, with caps maybe? And I would have thought a 4 stroke 4 cylinder engine would only open the valves once per revolution, but I may be wrong.
 
  #8  
Old 06-02-2013, 09:55 PM
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Originally Posted by kayweb View Post
Threaded piping, with caps maybe? And I would have thought a 4 stroke 4 cylinder engine would only open the valves once per revolution, but I may be wrong.
A 4-Cylinder 4-Stroke engine opens two sets of intake valves and two sets of exhaust valves (but not the same two sets) per rotation.
 
  #9  
Old 06-03-2013, 03:27 AM
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I need to look at those animations on wikipedia again.
 
  #10  
Old 06-03-2013, 08:21 AM
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I thought it was 1 until i did the math and got 45hz. Then when looking around I saw everyone with 4 cylinders was getting double that.
 
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