Drone?????

[1987cp]

Interesting. Guess with the 3.27s it was hardly ever spinning that slow. And that's with the 2.25" exhaust I said was fairly low on drone despite being wheelie loud out back, correct?

Speaking of which, keeping a 2.5"-equipped car up in the revs via deeper gears (say, 4.10s) and a looser converter (maybe 2500 or higher) might help the occupants experience less drone despite it being pretty horrible when it happens?


Incidentally, when I had my side-exit setups (exiting in front of the rear wheels), it was loud but no drone. And you can get away with that in Indiana (or so my experience dictates).

[cleanmerc01]

i have single exhaust and i havin my buddy weld new exhaust on. i was wondering how i am i going to do this dual set up? am i going to need to get another cat and o2 sensor? or should i just run the way now with a 1 in 2 out muffler? i want to have it exit right in front of back tires. any help will do. we have mandel bender and welder so we can make all bends.

[Leafsrule16]

Your exhaust is dual all the way back to the muffler where the two pipes meet into one muffler and go back as single. Just buy two mufflers of ur choice (remove the second set of cats too or it wont sound good at all), buy an h-pipe, tail pipes and a few feet of piping and your set. Weld your tips on too if you want some.

[gadget73]

Yup, just buy the stock replacement dual exhaust parts. It just bolts in, easy as you please.

[v8only]

The problem with the stock dual exhaust is that it's WAY too restrictive. The dual exhaust connects right after the cats up front, which is dual 2.5"...then the pipes get restricted down to 2" or perhaps smaller.....You'd probably be best sourcing some dual exhaust stuff from a junkyard cruiser, then using it as a template and cut out the smaller diameter piping and have dual 2.5" stuff welded in.

[sly]

2" all the way to the manifolds on my 88... 2.25" all the way for my 93. 2.5" all the way for my Mark (mustang stuffs under the hood).

[TomO]

I guess everyone can have their own definition of drone, but I've always thought of exhaust drone as describing a resonant effect of dual exhaust. Here's my theory. Resonance is a natural frequency at which an object vibrates. Think of a tuning fork as an example -- a tuning fork tuned to the note of "A" has a resonant frequency that makes an "A" note (I think it's somewhere around 400 Hz, but I don't remember exactly). If you put a "A" tuning fork against a violin or guitar or other stringed instrument and play an "A" note, the tuning fork will start to vibrate because it's the resonant frequency. But if you play any other note, the tuning fork will not vibrate much. With a muffler, resonance is the frequency of the exhaust pulse or speed at which the air inside the muffler vibrates to make a louder noise than at other speeds. I'm not sure what causes it, but I think it's when the wavelength of the exhaust sound is some multiple of the length of the chamber in the muffler. This can cause a louder sound because the wavelengths and muffler chamber interact so that the sound is sort of amplified by itself. That's why with some old cars that have rattles, you will won't hear the rattle until the engine reaches a certain speed -- when the engine speed reaches the resonant frequency of the rattling part. Another way to think of it is to imagine a big tub of water. The resonant frequency of the tub is the frequency that it takes a wave of water to bounce from one side of the tub to the other side. Imagine the tub is a muffler. Imagine your hand moving back and forth as the exhaust frequency. If you move your hand back and forth real slowly, the waves are absorbed between your hand and the sides of the tub and everything's cool. But if you slowly increase the speed of your hand moving back and forth you will eventually reach a speed at which your hand is moving back and forth at the same speed that a wave naturally bounces between the sides of the tub. At this speed, your hand moving back and forth is amplifying the natural wave frequency of the tub and you will notice that the wave gets really big and starts splashing out of the tube. This is resonance of your hand moving back and forth and the tub's natural resonant frequency.

Now think of an exhaust system. The exhaust pulse varies with the speed of the engine. The system has a natural resonant frequency. This resonant frequency of the exhaust system is usually accentuated in a dual exhaust system with two mufflers of the same size. That's because the resonant frequency of both mufflers is the same and when one muffler starts resonating, it will amplify the resonance of the other muffler and vice versa. This seems to be particularly true with systems that have a cross-over tube (balance tube) and performance mufflers that don't have resonance chambers (like turbo mufflers etc.) There's a certain range of engine speed in which the resonant frequency of the muffler is reached, which causes both mufflers to resonate. It sounds like a loud hum and it occurs only near a certain engine speed.

[Mercracer]

..... There's a certain range of engine speed in which the resonant frequency of the muffler is reached, which causes both mufflers to resonate. It sounds like a loud hum and it occurs only near a certain engine speed.

No drone I have ever experienced was the effect of having duals resonating against each other. Aftermarket exhaust will often cause parts of the car (and people's homes, etc) to resonate due to the stronger unharmonious vibrations coming from it...
I have never seen someone try so hard to justify loud exhaust and the often irritating drone it causes by blaming it on "just physics".......

[1987cp]

He does seem to be thinking partly in the right direction, but if drone were ever caused by "resonant frequency of the muffler" (which I suspect rarely if ever even really exists, at least within the frequency ranges that typically cause objectionable resonance), it would: a) go away when substituting a different muffler with completely different design (and if you're thinking of resonance inside chambered mufflers, it'd be nonexistant when using a dissipative type muffler), and b) be unaffected by the experiments guys have done by constructing auxiliary "tuning tubes" based on the resonant length of the tailpipe.


+10,000 on resonance of parts of cars or of nearby buildings.

[gadget73]

strictly speaking, it is just physics. Annoying as hell, but it is just physics.

Apparently drone is more pronounced when both sides of the exhaust are identical because the whole system will resonate at the same time. Some vehicles specifically use different length mufflers and different diameter pipes to make this not happen. If you've ever ridden in a stock Lincoln Mark VII, they do not drone at all. Different mufflers, one tail is 1 7/8", one is 1 3/4" or something. Replace that with a conventional cat back with 2 matching mufflers and tailpipes of larger and same size pipe and you get that typical Fox 2100 rpm drone. Use 2 different mufflers though, and its mostly not there.

Interestingly, Panthers with a Mustang H pipe have the same drone points as a Mustang does. can't help but think the pipe up front has something to do with it.

Anyway, the stock dual exhaust pipes are not a significant restriction with a stock motor. The stock mufflers blow, but the H itself isn't really an issue. Tailpipes aren't spectacular and could do with an upgrade but the mufflers are probably the easiest thing to upgrade. Most people aren't gonna want the stock mufflers anyway, too quiet.

[johnunit]

Wasn't there something posted here about a person who had cancelled out drone on a mustang by having a pipe going nowhere T off of one of the tailpipes? It seems it was the same length as the length of tail pipe after it, and was capped off. It's resonance cancelled out the resonance of the tailpipe past it, and having those resonances cancelled out stopped the other tailpipe from having a "partner" in resonation.

[1987cp]

Yep, that's precisely what I was talking about. Seems the original thread was on Corral.net, and it's referenced in a thread here (started by me, IIRC) and one at SBFtech.