Exhaust drone inside car

[fgross2006]

I have an 84 5.0 with CFI. I converted from single to dual exhaust a few years back.

I have stock shorty headers, a stock H pipe with 4 stock cats, the two front cats hollowed out, rear cats function and the secondary air system functions, I have MagnaFlow mufflers 3 inch in/out, tail pipes are 2.5.

It has a nice throaty growl but the drone inside the car is maddening. Is there something I can do to eliminate or at least reduce the amount of drone inside?

I don't want to start replacing exhaust components, perhaps their is something I can add like inline resonators or something like that?

[86MustangGtRob]

I forget who makes them. I had the same problem on my 85. I had a set of butterfly flaps installed. They worked off back pressure. They installed them just before the mufflers.

[emerygt350]

it isn't a 100% cure but maybe 80% and that isn't bad. Rolled up metal lath stuffed into the tail pipes. Maybe 8 inches long. You can test it out without doing any mods and then if you like it just put a small retaining screw in the pipe to hold them in place. Total cost, maybe 4 dollars.

[vintageracer]

New mufflers

[fgross2006]

New mufflers

I'm not swapping mufflers again. I had flow masters before and they were unbearable inside the car. the Magnaflows are much better but the drone is still there at cruising speed.

Has anybody tried X-mat inside under the carpets? Since I have a convertible I would assume I'd have to lay this stuff out all the way back to the trunck to be effective.

https://www.eastwood.com/x-mat?utm_s...ign=2016-08-08

[JACook]

When I recently changed out the mufflers and tailpipes under my '85 Vert, I took a page out of Ford's book,
using different length Magnaflows for the left and right sides. Mine still has the late-'85 factory exhaust, which
uses the same shorty headers and same size cat and Y-pipes as the '85 4V engines used.

The Mufflers I used are Magnaflow 11265, and 11235, band-clamped to the original after-cat 2.25" reverse
Y-pipe. Tails are Flowmaster full stainless 2.5" 815814. Had a muffler shop expand those slightly, so they
would fit over the muffler outlet stubs, and band-clamped those in place as well.

I am very happy with the fit, performance, and sound of this system. Very mellow, and NO drone.

[fgross2006]

Has anyone had any experience with sound deadening under the carpet? I want to try to find a good sound deadener. I am not gonna start replacing the mufflers. I like it the way it is, I just the rumble to flow behind me, not in the car with me.

[82GTforME]

I have used the Hush Mat style type but can't quantify what the improvement may be.

You said you gutted the front cats but not the back. Would gutting the back, not the front be an option and wonder if it would make any difference? The resonances coming out of the headers may have no restrictions (so not enough back pressure) as it should be designed? Similar to what emerygt350 above suggested (add back pressure but at the tail pipe). I am no expert by any means but look try to look at acoustics and velocities.

Is the drone at all RPM or certain RPM and load?

[KevinK]

I just installed a replacement cat back OEM style on my 85. It’s a single CAT. I had a hard time finding almost every piece. The y pipe was original as it had a Ford number on it. Mufflers and tail pipes were Flowmasters that were installed long before I got the car. It would seem I got the last Walker y pipe in the US.

For mufflers, I had to match the 2.25 y pipe. That got me the easy to find Walker left side replacement. The right side was a bit more difficult but Walker listed a shorter length Dynomax muffler. The y pipe is also longer on the right side. No mounting bracket or heat shield on the Dynomax. AP no longer has mufflers or y pipe for this one.

You would think the chrome tipped tail pipes would be easy to find. Walker no longer makes it. I switched to AP Emissions as they did make the matching 2.25 tail pipes. Again, the left side tail pipe was en easy find. The right side seems to be only a couple left in the US.

You would think this would complete the exhaust system search. Nope, the rubber muffler hanger/insulator seems to be getting hard to find. They are different from the tail pipe hangers.

After all this, I have not had a chance to test drive it yet. Hopefully no drone. Wish me luck.

There are plenty of options for 2.5” or 3” true dual exhaust. Not an option for me in CA using the stock CAT.

[fgross2006]

I have used the Hush Mat style type but can't quantify what the improvement may be.

You said you gutted the front cats but not the back. Would gutting the back, not the front be an option and wonder if it would make any difference? The resonances coming out of the headers may have no restrictions (so not enough back pressure) as it should be designed? Similar to what emerygt350 above suggested (add back pressure but at the tail pipe). I am no expert by any means but look try to look at acoustics and velocities.

Is the drone at all RPM or certain RPM and load?

It drones at cruising speeds. 45, 50, 55 etc. once I hit a cruising speed the drone rumbles inside the car.

This engine with CFI needs some back pressure. the shop manual says eliminating back pressure will cause stalls and they were right. My first attempt at dual exhaust conversion I had a 3 inch X pipe, no cats and flow masters. The car would stall everytime I came to a full stop. I had my guy install magnaflow hi-perf cats and the car ran great but the X pip was too big and the driver side cat got crushed bottoming out.

The only solution I could come up with was to go stock H with stock cats. I felt the 4 cats were over the top and not needed so I had my guy hollow the fronts. Because the rears still had the smog pump working I felt 2 cats was good enough. The original single exhaust on the 84 only needed 1 cat so a dual should be fine with just 2 cats. I now have enough back pressure to keep the car running nice. the sound is throaty. I just want it quieter inside the car.

[Jack Hidley]

No thin mat style sound deadening inside the car is going to have any affect on the frequencies that you are trying to absorb. The mat is less than one inch thick, but the wavelength of the sounds is over one foot. It will do nothing.

Your best bet is to install a 1/4 wavelength resonator in the exhaust. See the link below for more information.

https://www.corral.net/threads/exhau...y-gone.496793/

[v8stang289]

What he said ^^, The "j pipes" on mine run about 25" or so. I built mine with a sleeve clamp so I could tune the length. These cancel out the frequency that causes the droning resonance. The drone was so bad in my 86 at 50-65 mph that it was giving me headaches and i couldn't drive it for long. I was researching cat backs to switch out and came across this. It fixed it completely, and this is with the Flowmaster Cat back

[xctasy]

This is an outworking of Jack Hidley and steam_mills ideas.

it isn't a 100% cure but maybe 80% and that isn't bad. Rolled up metal lath stuffed into the tail pipes. Maybe 8 inches long. You can test it out without doing any mods and then if you like it just put a small retaining screw in the pipe to hold them in place. Total cost, maybe 4 dollars.

The details are simple, and its the least cost option which makes the noise drop you require.

Here is what they look like before going in.

I had a terrible 1800 rpm drone. Following steam_mills suggestion, I went and bought the metal lath today, cut 2 8x12 inch pieces out of it, wound them around a broomstick and slid them as seen in the picture.

The nearly intolerable drone from my not really mufflers is gone.

[fgross2006]

No thin mat style sound deadening inside the car is going to have any affect on the frequencies that you are trying to absorb. The mat is less than one inch thick, but the wavelength of the sounds is over one foot. It will do nothing.

Your best bet is to install a 1/4 wavelength resonator in the exhaust. See the link below for more information.

https://www.corral.net/threads/exhau...y-gone.496793/

I just saw this post. Thanks. i looked at the thread and unfortunately cant view the attached pics. i'd like to see what it looks like.

I just found out my stock cats are done. it sounds like marbles jumping inside. Since I have a stock H pipe with stock cats, its not feasible to weld in universals or a high flow set of Magna flows. The stock cats were robot welded at angles that nobody wants to try to blend. So I think my next step is to replace my stock H with an aftermarket with cats. Can anyone tell me if this will bolt up easy or need mods to make it work?



Its listed as Catalytic Converter Fits: 1986-1989 Ford Mustang 5.0L V8 GAS OHV on Ebay. mine is an 84, but since it was converted to dual with parts from an 86 I think its correct.

After I correct my fried cats I'll assess the sound and drone and see if more work needs to be done. The butterfly flaps idea and the metal lath sound easy and cheap. The killmat didnt do nuthin. I even laid jute padding between the killmat and the carpet for good measure.

[erratic50]

Different mufflers are a very good solution.

Remember that in stereo applications when they port an enclosure the sound plays a lot louder out the port than it played in a sealed enclosure. The tail pipe is effectively the port. The info Jack posted will for sure help kill off the tones in the range where drone is most common. A different muffler design helps. Diverting the exhaust to the ground and each pipe away from one another also helps.

I'd swap mufflers if it were my car. Dynomax or Magnaflow depending upon budget.

[fgross2006]

Different mufflers are a very good solution.

Remember that in stereo applications when they port an enclosure the sound plays a lot louder out the port than it played in a sealed enclosure. The tail pipe is effectively the port. The info Jack posted will for sure help kill off the tones in the range where drone is most common. A different muffler design helps. Diverting the exhaust to the ground and each pipe away from one another also helps.

I'd swap mufflers if it were my car. Dynomax or Magnaflow depending upon budget.

I already have Magnaflows. Swapped from Flowmasters that were way worse for noise level.

Anyway, I have to change my H pipe, either way. My stock cats are toast now.

[emerygt350]

I think the suggestion is to have different mufflers on the same car. I might be wrong though.

[erratic50]

drone is a function of RPM vs throttle position causing a tone that resonates in the exhaust. Lots of solutions. Some guys change rear gears to get out of the drone zone at the speeds they drive most often.

If you aren't running tail pipes, add them. They make a HUGE difference. My 86 is nascar loud without tail pipes, but is just fine with tail pipes. Granted I'd love to give these flowmaster mufflers the boot..... but I found them CHEAP and cheap is what I needed at the time.

[fgross2006]

well the killmat deadened the outside sound a bit it still drones. I was thinking maybe tailpipe tips with resonators built in. Anybody try something like that?

The killmat wasn't a total waste, It helped with the stereo acrostics in the car.

[gr79]

Could try the metal lathe in tailpipe to hear if there is a change.
Cheap metal gutter guard mesh from HD is same thing.
Roll one up or two and see if things mellow out.
Real resonators have welded perf inner tubes, which do cut down the id of the tailpipe.
Tailpipe may be packed or not between inner and outer pipes.

I like a quiet drone adds to listening to the engine and drive train sounds. Exhaust tuning. Harder to do with single vs dual exhaust.
On mine (single sport tuned), car is way louder dumped vs tailpipe and tips. Bit of a drone too.
Is about the muffler type (in this case turbo), and straight tail tips. Everything else is the same.
Added extra hanger brackets before and aft of muffler.
Universal hd thick type rubber layered, multi hole type, with the mounting hook riveted to one end.
https://www.napaonline.com/en/p/EXT3...iABEgI1hfD_BwE

Exhaust has to have a note during accell, then be quiet enough to hear any abnormal noises to sound an alarm.
And the radio, others talking, or sirens.
And not the popping and spitting of new era. Sound like they have an exhaust leak or need a tune up.
Have to add color sound because engine does not make enough of the right ones or too much of the wrong?
https://itstillruns.com/fix-exhaust-drone-8080950.html

[0F0 CBR]

I tried the metal lath in the tailpipes today, had the most success with two different lengths, one about 8" the other 12". Marginal success, by no means eliminated the drone, but definitely better.

[massacre]

Great info here, thanks!

Does anyone know if the modular v8 engines have similar problems with drone that the OHV seem to have sometimes?
I suppose it is different car to car but just figured I’d ask.
sorry if this is off topic

[Tigger]

Great info here, thanks!

Does anyone know if the modular v8 engines have similar problems with drone that the OHV seem to have sometimes?
I suppose it is different car to car but just figured I’d ask.
sorry if this is off topic

Yes, my wifes 00 GT droned about 2200 RPM. It had the stock H-pipe and 2 chamber flowmasters. It sounded good from the outside and it was louder than my 96 with the bassani x-pipe and 3 chamber flowmasters.

[0F0 CBR]

After a 4 hour drive listening to mind numbing drone I bought an 18" Magna flow to replace one of the 14"ers, in hopes to quiet it down at cruising speeds.
What side did you put the larger muffler on? I am thinking drivers as a little more room and no fuel lines to contend with.

[darkd0r]

Some Lincolns used different diameter exhaust pipes left and right. They also had weights bolted to the pipes. Try the cheap things in combinations before spending big bucks. Acoustics is a funny business.