Cant' get rid of exhaust drone! - Vintage Mustang Forums
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post #1 of 34 (permalink) Old 05-04-2019, 08:41 PM Thread Starter
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Cant' get rid of exhaust drone!

I just got the new engine and transmission into my 65 convertible (347 with T5). With it, I had a Magnaflow 2.5 inch SS exhaust system with x-pipe hooked up to my Dougs Tri-Y's. Driving home from the exhaust shop it was obvious that it wasn't going to work-the drone was so bad around 2k rpm I could barely take it. Sounded awesome everywhere else, especially WOT. So, I took off the tailpipes to give it a try and the drone was pretty much reduced to nothing-just way louder at idle. This wasn't the ideal setup with exhaust dumped before the axle, and I was getting complaints about the noise idling while tuning in my garage. I ended up going back to the exhaust shop and having my tailpipes put back on with some Dynomax Super Turbos. Now guess what-the drone is back Maybe not quite as bad as with the Magnaflow mufflers but it is pretty bad around 2K rpm again. Idle is very quiet though. I don't like the way the Dynomax mufflers sound as much as the Magnaflows either. Now I am stuck with mufflers that drone and don't sound as good. Any suggestions? Anyone experience the same with with a 2.5 inch exhaust on a 65 or 66?
Oh, and I stuffed my trunk floor, sides, and area behind seat with thick foam and insulation but that didn't do much.

Last edited by Chip Phillips; 05-04-2019 at 08:55 PM.
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post #2 of 34 (permalink) Old 05-04-2019, 08:50 PM
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I have Ebay stainless Tri y's into a homemade X pipe and Jegs 30220 "deep tone" 2 chamber 40 clones and FlowMaster 15807 tails with 3.5" stainless "truck tips 18" long
I too get drone, I just bought a pair of these https://shop.advanceautoparts.com/p/...E&gclsrc=aw.ds


To stuff in the tails hoping they work going to make them removable for autox daze




Brad

Last edited by 2nd 66; 05-04-2019 at 08:54 PM.
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post #3 of 34 (permalink) Old 05-04-2019, 09:26 PM
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Most 2.5in systems with a cross over (H or X pipe) and performance mufflers are going to drone on an SBF.

I've got 2.5in stainless that runs back to an H from Hipo manifolds, through flow master super 44's and out my cut down GT trumpets. The drone isn't all that bad. I'm sure the headers also contribute a bit in your case. I spent a LOT of time listening to exhaust clips and reading up on all the products offered from Flowmaster, Borla and Magnaflow before settling on the Super 44's as they seemed to have the least drone (I've had original 40's on a SBF and they are AWESOME, but drone from 2k-3k) for the best flow and sound.
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post #4 of 34 (permalink) Old 05-04-2019, 09:56 PM Thread Starter
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I have seen those auger inserts before and read about them over on the Cobra forum. Do you know if they create back pressure similar to a more restrictive muffler?
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post #5 of 34 (permalink) Old 05-04-2019, 10:00 PM
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I have cast iron manifolds, an H pipe and Flowmaster 40s with 2 and 1/2" tails. It has a late model sound at startup and idle, very streetable, a definite change in tone (maybe a tiny drone) at 2000-ish rpm then it levels off quickly and gets quieter well into 4000 and beyond. I used to have a car-rattling and neighbor-harassing pair of turn downs under the car after the 40s. 35 mph was about unbearable.
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post #6 of 34 (permalink) Old 05-04-2019, 10:17 PM
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Originally Posted by Chip Phillips View Post
Any suggestions?

Somewhere (here? Boss 302 forum?) there is a group of guys who swear by stock Walker mufflers for a Cadillac.
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post #7 of 34 (permalink) Old 05-04-2019, 10:59 PM
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I've got a '66 with 1 3/4" primary headers, 3" collectors, x-pipe, 3 chamber Flowmasters and 2.5" tubing
out to the back. It doesn't drone.
My '68 has Thorley tri-y's, an x-pipe, hooker mufflers, 2.5 tubing out to the back. It doesn't drone.
In general, it has to do with they way the system is built. How close it is to the floorpan. And other details.
You can quiet many of the "not quite right" systems with different size muffler cases, helmholtz
resonator tuning and other tricks. Bigger tail pipes DO have a tendency to drone on a lot of systems.....
that's pretty much a given and probably the most accurate generalization.
Exhaust design IS a science.
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post #8 of 34 (permalink) Old 05-04-2019, 11:23 PM
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I just finished a 2.5” mandrel bent system, H pipe Headman 2.5” turbo mufflers. Not exactly quiet but no drone
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post #9 of 34 (permalink) Old 05-05-2019, 12:16 AM
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Quote:
Originally Posted by Chip Phillips View Post
I have seen those auger inserts before and read about them over on the Cobra forum. Do you know if they create back pressure similar to a more restrictive muffler?
I'm sure they create some restriction ,I'm considering them a cheap science project for now
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Originally Posted by myfirstcar66 View Post
I have cast iron manifolds, an H pipe and Flowmaster 40s with 2 and 1/2" tails. It has a late model sound at startup and idle, very streetable, a definite change in tone (maybe a tiny drone) at 2000-ish rpm then it levels off quickly and gets quieter well into 4000 and beyond. I used to have a car-rattling and neighbor-harassing pair of turn downs under the car after the 40s. 35 mph was about unbearable.
I've built a few exhaust systems with different X pipes I've built. One on a brand X big block truck nice lope at idle thunderous at midrange then it got strangely quiet owner was happy

My drone is in narrow RPM band say from 2k(just past cruze) till just before 2.5k then it smooths out and sounds nice and WOT ,well

@dobrostang runs FM 50 series and has 0 drone but all the cool rumble also sounds


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post #10 of 34 (permalink) Old 05-05-2019, 01:43 AM Thread Starter
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Mine is pretty much that same rpm band. It seems to be related to the length and size of the tailpipes. When they were shorter and dumped along the gas tank the drone was not quite as bad, and when I had it dumped at the muffler without tailpipes there was no drone at all.
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post #11 of 34 (permalink) Old 05-05-2019, 02:54 AM
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I understand exhaust gas pulses move like a ball rolling through a tube and restriction is necessary to some degree to help build torque at certain RPM, free flow is necessary for horsepower, so there must be a balance. A muffler should act as the valve. I have a mandrel bent system to prevent unscheduled restriction and prevent the pulses from stacking up at crimped or necked down places in the curves or near joints. Smooth is fast.

'66 Tahoe Turquoise/ Aqua coupe
•289 / 4100 •C4 Auto •Disc Brakes
•Dual Exhaust •16:1 Manual Steering
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•LOTS of Rotunda accessories
•Original Styled Steel Wheels
...my first car

'66 Emberglo / Parchment coupe
•289 / 2100 •C4 Auto •Disc Brakes
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...son's first car


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post #12 of 34 (permalink) Old 05-05-2019, 03:51 AM
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restriction is necessary to some degree to help build torque at certain RPM
That's really a very common misconception. Restriction never helps. I think the reason this idea got such big traction is from putting on 'restrictive' exhaust pipes and headers, only to discover that engines make more power that way sometimes.

Gas flow dynamics have everything to do with compression waves. If you can get good velocity, and have your exhaust designed right, then the soundwaves (pulses) in your exhaust really help to suck the next exhaust stroke out of the cylinder, at certain RPMs. A giant sewer pipe exhaust where the spent gases can exit freely, but at low velocity, will never have much effect on scavenging.

Don't believe me? Stick a straw in your mouth, and blow through it, hard. Stick your tongue on the end to stop the air. You can definitely feel the rapidly moving air in the straw try to 'suck' your tongue down the tube as it all comes to a stop! Now try the same thing with a paper towel tube. Heh. Even if your tongue were big enough to pull that off, you just can't get a lot of velocity going, unless maybe you're Superman.

So in effect, it's not that a 'restrictive exhaust' is helping to make power - it's more that your exhaust will often respond much better to a 'just right' size, or even slightly too-small, instead of being too big. Especially if you tune the lengths, and run a crossover. Your average power will go way up, even if the 'big pipes' give you more top end.

Another thing that really freaks people out is how a glasspack muffler can actually flow more than a straight section of pipe with the same internal diameter. The rough walls should slow things down, and create drag inside the muffler, right? Well, the thing is, as the exhaust moves through a 'smooth' piece of pipe, the outside edges grab the walls of the pipe and swirl around, creating vortices and drag. When you shove gases through faster, the effect gets more pronounced.

In a glasspack muffler, the perforations in the tube not only hang onto the air, but high-pressure turbulence just falls through the holes (for lack of a better description) instead of being forced back to the middle, creating restriction. As a result, you get very smooth laminar flow. The slow, low-pressure gases clinging to the edges of the perforated tube allow the column of gas in the middle to blow through with much less restriction. Granted, the old glasspacks (and turbo mufflers too) are a bit loud, but there's a good reason they have always been popular since they were introduced. They work without decreasing performance! =)
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Last edited by Grimbrand; 05-05-2019 at 03:58 AM.
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post #13 of 34 (permalink) Old 05-05-2019, 08:11 AM
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Somewhere there is a great article on drone but its curable, I had mind numbing drone. First get rid of any restrictions. The ones that get overlooked is when people go from 2 1/2 to 2 1/4 pipe out the back to make it easier to get over the 3re member. This creates a sound node or for those guitar players in the crowd a finger just touching the string on the 12th fret creating a harmonic where the sound waves reflect backwards creating a 2k harmonic. Here is where mandrel bent really helps.



Next get the sound out from under the car. Tail pipes should extend out from under the car by 2" This works fine for rear valences as they wrap under the car so 2" past the rear valence is still well under the bumper and looks fine. Dump any fart-can big tail pipes, they are made to resonate.



Next, how the exhaust is mounted makes a huge difference. Look at new car tail pipes, they are hung with two big rubber loops or a huge pieces of rubber at each mount - serious insulation to the frame. With all the noise and vibration our cars make, why accept anything less! Many hack exhaust guys will hard tack a bolt to a frame then hard mount the pipe with two thin rubber washers (my case) and think their work is done. Also, many underestimate the amount of movement a resonating pipe can move, so search the exhaust carefully for evidence of contact with a body part like the gas tank.



I used those rubber mounts that look like its made from cut up tires you get at autozone with all the holes drilled in the rubber. I cut the steel off and bent the 6" or so of rubber in a U around a 1" piece of steel tubing with a bolt through it all and mounted the bolt on the tie down in the rear. Then bolted the exhaust in the middle of the U.


I have shorty headers 3" collectors, 2 1/2" mandrel bent with a crossover placed at the hottest point in the exhaust after a power run, found with a infrared gun. 3 chamber flowmasters dual duals out the back - no drone!
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post #14 of 34 (permalink) Old 05-05-2019, 08:34 AM
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Google 1/4 wave resonator. There is a good article on a Fox body site out there on how to cancel the drone. It involves a piece of "dead leg" pipe that sets up a reflective wave that cancels the 2000 rpm drone...
Try this link
https://forums.corral.net/forums/gen...tely-gone.html
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post #15 of 34 (permalink) Old 05-05-2019, 09:25 AM
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Originally Posted by Huskinhano View Post
I just finished a 2.5” mandrel bent system, H pipe Headman 2.5” turbo mufflers. Not exactly quiet but no drone
Tom can you post to PM me on this system you used?
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