UPDATE IV: Exhaust Drone - X-pipe flute?. See Post 72
11-30-2011, 10:09 PM
#34
Rennlist Member
Excellent discussion!
Bringing over the picture of Jeff's (Speedtoys) solution - it is worth 928 words! (See, below)
I am surprised the "helmholtz pipe" (resonance pipe) did not need to be longer, even if made to 1/4 of the targeted wave length. I had come up with different values for 1/4 wavelength when I did similar calculations, but I need to re-check those calculations. Never thought to place it as he has - that is brilliant!
+1 on gas temperatures assumed/realized and their effect on the speed of sound, and thus the calculated length. Also, Exhaust Gas Temperatures (as measured in the pipes) will also go up with RPM, so different RPM's will have different values.
+1 on wrapping or insulating the offending or suspected components - it will add weight to them, and thus change their natural resonant frequencies.
Similarly, changing/adding mount points can mute natural resonant frequencies by restricting high vibration points (anti-nodes).
Along these lines, attaching the resonance pipe could also have potentially changed the natural resonance of the main pipe from what it was without it.
Regarding branching pipes off the branched resonant pipe, I have not considered that, but I have thought of having several resonant pipes along the exhaust route, each varying in length, to target more than one frequency and/or RPM. This all adds weight, however, so I need to weigh
the tradeoffs.
Similarly, have thought of introducing several balance pipes - Porken's example is encouraging!
I do not currently have annoying drone (4/17/2012 Edit: seen Note below), but I plan to modify the exhaust on the 86.5 Automatic Stroker, and that will include adding an Ott styled )(-pipe (or two). Current configuration (in flow order) is Devek Level2 Headers, no cats, absorption style Magnaflows, inefficient X-pipe, Large Magnaflows, and RMB. (I'll add the details on the Magnaflows when I dig them up again!). Again, no annoying drone currently (4/17/2012 Edit: see Note below).
4/17/2012 Edit: Note - went on a road trip not too long ago, and it made me realize that I DO have drone, but I don't mind it! So, maybe it is just not as bad a drone, or maybe drone just does not bother me, however, I do have some drone with my configuration.
I would have been suspicious of the aftermarket intermediates being used, if not for so many other folks that have experienced the annoying drone after adding the )(-pipe with stock components.
I am hoping to go beyond simply reducing any potential drone, however, and hope to create music! It can be done! I have heard it from a Fourth Gen Camaro ('93-'02) at 4am every morning for several months. I want to replicate it!
Below is the picture from the other thread, of Jeff's solution:
I am surprised the "helmholtz pipe" (resonance pipe) did not need to be longer, even if made to 1/4 of the targeted wave length. I had come up with different values for 1/4 wavelength when I did similar calculations, but I need to re-check those calculations. Never thought to place it as he has - that is brilliant!
+1 on gas temperatures assumed/realized and their effect on the speed of sound, and thus the calculated length. Also, Exhaust Gas Temperatures (as measured in the pipes) will also go up with RPM, so different RPM's will have different values.
+1 on wrapping or insulating the offending or suspected components - it will add weight to them, and thus change their natural resonant frequencies.
Similarly, changing/adding mount points can mute natural resonant frequencies by restricting high vibration points (anti-nodes).
Along these lines, attaching the resonance pipe could also have potentially changed the natural resonance of the main pipe from what it was without it.
Regarding branching pipes off the branched resonant pipe, I have not considered that, but I have thought of having several resonant pipes along the exhaust route, each varying in length, to target more than one frequency and/or RPM. This all adds weight, however, so I need to weigh
the tradeoffs.Similarly, have thought of introducing several balance pipes - Porken's example is encouraging!
I do not currently have annoying drone (4/17/2012 Edit: seen Note below), but I plan to modify the exhaust on the 86.5 Automatic Stroker, and that will include adding an Ott styled )(-pipe (or two). Current configuration (in flow order) is Devek Level2 Headers, no cats, absorption style Magnaflows, inefficient X-pipe, Large Magnaflows, and RMB. (I'll add the details on the Magnaflows when I dig them up again!). Again, no annoying drone currently (4/17/2012 Edit: see Note below).
4/17/2012 Edit: Note - went on a road trip not too long ago, and it made me realize that I DO have drone, but I don't mind it! So, maybe it is just not as bad a drone, or maybe drone just does not bother me, however, I do have some drone with my configuration.
I would have been suspicious of the aftermarket intermediates being used, if not for so many other folks that have experienced the annoying drone after adding the )(-pipe with stock components.
I am hoping to go beyond simply reducing any potential drone, however, and hope to create music! It can be done! I have heard it from a Fourth Gen Camaro ('93-'02) at 4am every morning for several months. I want to replicate it!
Below is the picture from the other thread, of Jeff's solution:
Last edited by hernanca; 04-17-2012 at 11:50 AM. Reason: Clarify reference to Speedtoys picture. Clarify EGT measurements. Clarify my configuration. Edit: I do have drone!
12-01-2011, 10:18 AM
#36
Rennlist Member
Yes, it does look open in that first picture, but it is closed. Here are a couple more of his pictures off Flickr (http://www.flickr.com/photos/2880466...th/6419605131/):
12-01-2011, 11:45 AM
#38
Rennlist Member
I don't know if it is more of a problem with headers vs. stock manifold.
Another solution, instead of the above resonance pipe, and if intermediate cans (stock resonators or otherwise) are not enough, seems to be to add back in the rear muffler (pumpkin or equivalent).
12-01-2011, 12:03 PM
#39
Archive Gatekeeper
Rennlist Member
Rennlist Member
H-X. Minor drone at 1800 rpm. Who spends any time at 1800 rpm?
12-01-2011, 12:09 PM
#40
Official Bay Area Patriot
Fuse 24 Assassin
Rennlist Member
Fuse 24 Assassin
Rennlist Member
Keep in mind that drone also varies with pipe size. The bigger the pipe, the more the drone. This is also why single exhaust 16v cars sound so refined.
12-01-2011, 01:14 PM
#41
Racer
Thread Starter
Another solution, instead of the above resonance pipe, and if intermediate cans (stock resonators or otherwise) are not enough, seems to be to add back in the rear muffler (pumpkin or equivalent).
I have that configuration (first thing I tried). It helped a little but still have drone - especially uphill at highway speeds.
12-05-2011, 03:50 AM
#42
Rennlist Member
Created a Drone Survey
https://rennlist.com/forums/928-foru...our-combo.html
Let's see if it reveals anything. I think I see a pattern in what I've read so far, but I am not sure.
12-05-2011, 09:29 AM
#44
Race Car
It is a nuance to the broader discussion, but the aft H might bear some more exploration.
On my LS1 GTO (and others) they were shown to erode performance.
I am familiar with Ken's results that showed improvement.
Like the x, I wonder whether it has to do with location, and also whether the system it is installed on has similar or dissimilar length intermediate pipes.
On my LS1 GTO (and others) they were shown to erode performance.
I am familiar with Ken's results that showed improvement.
Like the x, I wonder whether it has to do with location, and also whether the system it is installed on has similar or dissimilar length intermediate pipes.
04-16-2012, 04:15 PM
#45
Burning Brakes
Any updates to this ? Now my car has drone , sounds like a social disease . MSDS headers /X / magaflow mid / gibson rear . Thinking of changing the mid magaflows for the new dynomax no drone with the spring valve built in . Anyone tryed this ??