Suggestions for muscle car sound muffler without drone

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Your thread and your travels are very interesting. Up until now I have never seen anything regarding these pipes. I don't get much from youtube videos because it's coming from little speakers and the person recording always quickly revs the engine up and down. That IS NOT the problem. The problem is a constant RPM while you drive where that resonance gathers and grows and makes you feel numb. Now for a few questions.

I assume the length of the 90 was also calculated into the overall length of the pipe?

The graphs you're showing, is that from the phone app and the screen on your phone? I see one shows Samsung in the corner so I guess it is.

Looking at the plot, I see the spike and from reading your post, I gather that that is the peak resonance. So when tuning the pipe, that's where you came up with 125hz as the target to tune to. Am I following this correctly so far?

You went with a smaller diameter pipe and it worked. Based on that it's the length that's important because the length is what controls the return time of the sound waves within the exhaust system, did your research show at what point the smaller diameter of the resonator pipe might negate it's ability to perform it's function?
How did you determine that a smaller pipe would still work?
Does a smaller diameter pipe factor into the length equation? I would assume not because we're dealing with the distance the waves travel and not the volume. But would too small a resonator pipe not have the desired effect on the larger mass of exhaust flowing by it? I'm wondering if a 1.5" pipe would work still on a 2.5" exhaust system? The smaller diameter pipe is certainly desirable as far as fit and discretion.

Thanks for sharing.

An amusing point is here you may have thought what am I going to use this stuff for from Physics class when they were going over wave physics.

I used the phone app I listed in the thread. On a my S3 android phone you can do a screen capture. I also took the file off the phone and put it on the computer that was connected to my 55 TV so I could more accurately measure the frequency on the graph.

Yes the spike was where you want to tune it to. Actually from what I read it seems 125 to 130 something seems to be a common frequency for drone.

Yes you include the length of the 90 and from what I read you don't have to worry about 90 effecting how it works. I assume a smooth larger radius 90 is better than a sharper bend.

There is an equation for calculating the length but I found the site I listed an interesting alternative. I just plugged in some close length dimensions and it calculated the frequency the pipe was tuned to and the DB level Plus the harmonics. Larger diameter creates a larger DB of attenuation. If you try the same length dimensions on the site with different diameters you will see a difference in the DB level. I found the DB created by the 1.5" was more than the DB of the drone measured in the car with the 2" tail pipes. 1.5" diameter pipe was easier to fit too. I had thought about fitting them next to the mufflers but the location I came up with in the photo I like better. Also welding them on the pipe would make it harder to take things apart. So would a stub connection so I choose to make a saddle connection and use some muffler sealer. If you create a cap with some length for the end of the resonator, instead of welding it, and clamp it you can have some length adjustment to tune it. I would have tried it if I was a better pipe welder.

I'll have to check on the length I used but I was running calculations in the 25" to 28" range. Maybe in the thread. I'll check.
 
I used the calculator last night and came up with 27.2' so that's in the range you have. I like the idea of tuning it with a loose cap. Thanks for all the ideas and information.

I drove 90 miles today and was wishing it was already done...
 
Here's where my Dart is at now. Looks to be about the same as yours at 125Hz. Any chance of sharing your pipe length as it worked so well for you?

View attachment 1714713039

If you go here
http://www.diracdelta.co.uk/science/source/q/u/quarter%20wave%20tube/source.html#.U0sfFVpOVaQ and use a 27" long 1.5" dia pipe connected to a 2" dia pipe you will get 125hz. You have to convert to meters for dimensions. You will get the following. Vertical axis is DB. Looks like I cut it off when I did the capture.
 

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  • 27 inch long 1.5 inch dia tube on 2 inch dia pipe 125 hz.jpg
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I used the calculator last night and came up with 27.2' so that's in the range you have. I like the idea of tuning it with a loose cap. Thanks for all the ideas and information.

I drove 90 miles today and was wishing it was already done...

You are welcome. Let me know how it works out.

I asked a muffler shop how much he wanted to install this once. This was a place that did custom work. Regular Midas won't do it. He wanted $200 and you needed to give him all the dimensions. I assume he would have welded it in place. He did one for a Dentist on his BMW and it didn't work. Talking with him I found out he just crimp down the end of the resonator and welded it. That's why it didn't work. The sound waves couldn't bounce off the end with it crimped. Needs a flat end.
 
I've got tons of PVC and ABS around. Easy to work with, I think I'll mock it up with that and then take it to the muffler shop and have them match it up.
 
Recently I was helping a friend work on his set-up (non-Mopar) with a terrible drone. He tried different mufflers without much help. We added an H-Pipe (more to help with the low end torque than the drone) and it did affect the drone slightly. We tried something a bit off the wall. He had two different length Flowmaster 50's, for grins and giggles we threw those on, looks a bit weird but the drone is all but gone!
 
Recently I was helping a friend work on his set-up (non-Mopar) with a terrible drone. He tried different mufflers without much help. We added an H-Pipe (more to help with the low end torque than the drone) and it did affect the drone slightly. We tried something a bit off the wall. He had two different length Flowmaster 50's, for grins and giggles we threw those on, looks a bit weird but the drone is all but gone!

Interesting. I'm assuming it had something to do with changing the frequency a little and level between the two pipes so they didn't resonate. Wonder if this is a repeatable cause and effect. If it is you could just always do it when you change mufflers as a proactive approach for possible drone. Two different length mufflers of the same brand. Be a major experiment to prove the results are repeatable. Especially since drone doesn't always occur in every setup.

How's it sound?
 
I've got my pipes ground to fit but every time I get a day off everything changes. Off tomorrow and was planning to mount them and my daughter just told me she needs brakes and an oil change. I should say she asked me if I could work on her car as only a daughter can. Working on the Honda tomorrow instead....
 
I am sold on this technique. I finally got a free morning with my bro in law and we put the pipes on. The drone is gone, period. I honestly can't believe it. I'll post photos later today. There is still a beautiful muscle car rumble from the exhaust out back but no drone. I drove up my test hill which I have to always drive on the eay home and we can talk, listen to the stereo. You hear the pure exhaust rumble and that's it. My ears have been saved.
 
Here are the two graphs overlapped in Photoshop. The old graph is ghosted behind the new one. You can see a rise in the 2-10k range but I don't hear anything all that different in the upper range. It is an even tone now which is very clear in the graph. This was recorded on the hill that always bothers my ears coming home from work by our house.

View attachment pipe compare.jpg
 
This is sort of strange but I'm running 3" with X pipe and UltraFlo's dumped at the axle. I haven't noticed any drone thus far with them. I expected some but nothing yet. Possibly because they are still new? I do have some Fat Mat on the floor so that may be helping. The floor isn't 100% covered with the deadener. I installed it in patches.
 
It seems to really depend upon your set-up. Some cars get it and some don't. Sometimes different mufflers or adding an X pipe eliminate it and sometimes they don't. After seeing this thread I searched more on the internet and found this is a sure fire cure for the drone. There's a ton of information out there from truck sites, to Hondas to Mustangs and exotic sports car sites.
 
Recently I was helping a friend work on his set-up (non-Mopar) with a terrible drone. He tried different mufflers without much help. We added an H-Pipe (more to help with the low end torque than the drone) and it did affect the drone slightly. We tried something a bit off the wall. He had two different length Flowmaster 50's, for grins and giggles we threw those on, looks a bit weird but the drone is all but gone!
I had a 2001 Mustang GT. They came from the factory with an h-pipe, and the two mufflers were different lengths. I recall questioning this and I was told that Ford did it to reduce drone complaints from customers. I guess it works on Mopars too!
 
Here are the two graphs overlapped in Photoshop. The old graph is ghosted behind the new one. You can see a rise in the 2-10k range but I don't hear anything all that different in the upper range. It is an even tone now which is very clear in the graph. This was recorded on the hill that always bothers my ears coming home from work by our house.

View attachment 1714747594

Thanks for the update. Glad to here it worked out for you. Nice overlay
 
Drove a ton today and it's so pleasant now. We've got a long slight uphill 45 mph blvd in town that I used to stay in 2nd gear for just to make it more bearable. Quiet as could be today in 3rd. Thanks for all the information buck.

I grew up in Palatine- not too far from you. I took a lot of heat from all the Giants fans at work today wearing my Cubs hat after tarpgate at Wrigley.
 
Drove a ton today and it's so pleasant now. We've got a long slight uphill 45 mph blvd in town that I used to stay in 2nd gear for just to make it more bearable. Quiet as could be today in 3rd. Thanks for all the information buck.

I grew up in Palatine- not too far from you. I took a lot of heat from all the Giants fans at work today wearing my Cubs hat after tarpgate at Wrigley.

Thats great. I have a sister inlaw who lives in Palatine. Small world.

I tell people for me loud exhausts are only fun for about 5 minutes. Longer drives need more tame levels and no drone. It's also nice to be able to have a conversation or listen to tunes too. :)
 
I got the app just to see where my drone is at. I know it's really bad from about 850 rpm to about 1200 rpm.
[ame="http://s1277.photobucket.com/user/lukeb70/media/Mobile%20Uploads/photo_zpsea8635ac.png.html"]photo_zpsea8635ac.png Photo by lukeb70 | Photobucket[/ame]
I assume the big spike at just over 50 is the drone ?
 
Wow, that's really low. Looks like about 55Hz. Must shake your fillings in your teeth! Sure that's not your sub with the opening bass line from Cream's Badge playing??? :rock:
 
That is low. Lower than the common frequency for a v-8. Interesting. Is it vibrating any of the car like the rear view mirror? :)
 
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