Harmonic Resonance Help

[Tele5.0]

It's no where near that obnoxious for me. It's a deeper note and not constant at all. It's a slight swell here and there between 2500-3500 rpms. Not bad at all.

Not sure who all is familiar with the 5.0 Fox Bodys but that was a characteristic that I and so many others loved. With headers, H-pipe and flowmasters ...leave the tailpipes on and it was even better. They would get this tinny kinda hollow smooth harmonic sound about 2500-3000rpms right about when the load would come off of the motor (good shifting point) under normal driving conditions. I thought it was dead with this new Coyote but I guess not. I cant wait to get my headers and go catless and see if I can capture some of that back. If in fact that is what is going on here.

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[deven2015GT]

Not sure who all is familiar with the 5.0 Fox Bodys but that was a characteristic that I and so many others loved. With headers, H-pipe and flowmasters ...leave the tailpipes on and it was even better. They would get this tinny kinda hollow smooth harmonic sound about 2500-3000rpms right about when the load would come off of the motor (good shifting point) under normal driving conditions. I thought it was dead with this new Coyote but I guess not. I cant wait to get my headers and go catless and see if I can capture some of that back. If in fact that is what is going on here.

That is EXACTLY what is going on with the Ford Racing by Borla Exhaust, Touring and Sport Cat-back system. I am starting to fall in love with it. It's almost beautiful and hypnotizing now... is that considered a driving hazard now?! :shrug:

 

[Tele5.0]

That is EXACTLY what is going on with the Ford Racing by Borla Exhaust, Touring and Sport Cat-back system. I am starting to fall in love with it. It's almost beautiful and hypnotizing now... is that considered a driving hazard now?! :shrug:

Now I want even more!!! :cheers:

 

[deven2015GT]

Now I want even more!!! :cheers:

:cheers: :ford:

 

[Vile_the_Bastage]

I haven't heard my car do this in a couple of days. I posted in a similar thread that the noise kind of resolved itself. The header/exhaust tone got deeper as well.

 

[deven2015GT]

I haven't heard my car do this in a couple of days. I posted in a similar thread that the noise kind of resolved itself. The header/exhaust tone got deeper as well.

Agreed. My is slowing going away kind of. It's still there at times, I can hear it, but it's deeper and more musical. Just blends in with the rest of the engine and exhaust noise. It's lovely.

 

[JohnK]

I can shed a little light on the resonance issue. I had FRPP by Borla Touring Cat Back and had this same resonance. I returned the FRPP and installed Corsa Touring Axle Backs with a Mishimoto H-pipe - same thing - still had the resonance - so I am thinking it's not the exhaust systems. Tonight I capped off the sound tube and that lessened the resonance but it's still there. I am going to do a ride along with a stock system and see if it experiences the same thing.

 

[BmacIL]

I can shed a little light on the resonance issue. I had FRPP by Borla Touring Cat Back and had this same resonance. I returned the FRPP and installed Corsa Touring Axle Backs with a Mishimoto H-pipe - same thing - still had the resonance - so I am thinking it's not the exhaust systems. Tonight I capped off the sound tube and that lessened the resonance but it's still there. I am going to do a ride along with a stock system and see if it experiences the same thing.

I still think the root might be a driveline thing, especially considering you hear it off-throttle, too.

 

[LoveMyWheels]

Good morning, S550 brothers and sisters!

Anyone who has seen me posting like a giddy child knows that I just had a Ford Racing by Borla Cat-Back Touring Exhaust installed on my Mustang. The first guy I took it to to install it said it didn't fit right and was 1.5" off. He ended up "having" to cut 1.5" off to make it "sit properly in the hangers". The following weekend it took it to the local muffler shop back home (originally took it a shop up here where I'm working at out of town) and he tightened what needed to be tightened and moved a clamp or two and fixed the tiny leak the first guy said would seal by driving (which was bs). So no leak, startup sounds great, and the exhaust sounds fantastic, B U T...
There is a harmonic resonance that comes around 2500-3500 rpms. It is not drone, I know this, but it is a musical type of sound. It is similar to rubbing your finger dipped in water around the lip of a wine glass.

I guess my questions are:
1. Has anyone else experienced a similar issue with aftermarket exhaust?
2. Could the 1.5" cut off have affected the way the exhaust system piping was tuned to cancel out harmonic resonance?
-AND finally...
3. Does anyone know of a solution to this or is it something I just have to live with?

I know I've read about adding weights to the muffler to help with the resonance, but I've also heard that could affect throttle response among other things. I'm just researching solutions and there isn't a whole lot of information on this that doesn't have to do with just the science of it (which honestly just seems logical to me - i.e. exhaust being pushed through the pipe creates some harmonic frequencies so in turn the exhaust pipes are shaped and tuned to send out the same frequencies created to cancel out the noise).

Thank you in advance for the input and God bless!

EDIT: I was told by a co-worker who claims to know a good bit about cars that that type of harmonic resonance is not a bad thing. It is merely the exhaust tuned to peak performance and thus the musical slight resonance at that certain rpm range (he says). Can anyone confirm this who has experience with this?

An easy way to describe a noise is to identify the frequency. Get a free 'sound analyzer' app for your phone and check the peak in the frequency band while driving. The built in microphone in your smartphone is accurate enough for this.

 

[JohnK]

I originally had a Ford Racing/Borla Touring Cat Back exhaust on my 2015 Mustang GT and had the resonance you describe. I switched to a Corsa Axle Back (sport mufflers) with H-pipe and I still had the resonance, so I concluded it's unlikely to be the exhaust system that's causing the resonance. I capped off the sound tube and that helped a lot. I still have some resonance but I feel it's tolerable now. Bmacil suggested it may be the driveline. If you figure out how to solve this problem, I'm interested in what you find out. Thanks!

 

[JohnK]

BmacIL - any ideas how to prove it's the driveline - short of replacing it and seeing if that helps? Would be an expensive option, if that's not it... Thanks!

 

[BmacIL]

BmacIL - any ideas how to prove it's the driveline - short of replacing it and seeing if that helps? Would be an expensive option, if that's not it... Thanks!

If you get it off throttle too, it's not exhaust. It could be transmission mount, engine mount or something like that. It's not further down than that, because it's not speed dependent, just rpm.

 

[Cascadia_302]

If you get it off throttle too, it's not exhaust. It could be transmission mount, engine mount or something like that. It's not further down than that, because it's not speed dependent, just rpm.

Correct, I can get some very minor RPM related resonance (Corsa Touring) but only with the engine under a load going up or downhill. Never happens on flat terrain and it isn't a problem for me, you ultimately always have control over it.

 

[BmacIL]

I can only get it to resonate to some degree (not really drone, characteristically) if I lug the engine to 1250 rpm in 5th/6th gear. Otherwise, zero.

 

[Dr. Norts]

If you still have that sound tube get rid of it. It causes weird harmonic resonance that seems to fight the exhaust.

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