Exhaust drone & exhaust noise while both are different by definition, both are created as a result of impactors/promoters. Exhaust drone is that which is caused by harmonics- a sound wave generated which in essence takes the exhaust sound and sends it back up the exhaust system (towards the engine) and is released or transferred into the passenger compartment. This transfer typically happens where large contact areas exist that have little to no sound dampening qualities and/or materials- as a result of the muffler construction or vehicle manufacturer.

Exhaust Noise (in passenger compartment) is what most people actually complain about. While harmonics do play a contributive role, it is not the primary cause.

Impactors/Promoters

I would love to tell everyone that “x” is the cause 99% of the time for exhaust noise complaints, but it is typically a series or combination of numerous factors which leads or develops the level of noise which is uncomfortable to the ear. The first “rule” of an exhaust system is that the noise should be generated at the point of discharge (i.e. tailpipe tip). Obviously, if the tip terminates at your door or immediately under the passenger compartment, the sound level will be much greater at the exhaust discharge point than if the tip exits the rear of the vehicle, but this is common sense.

Assuming that there are no exhaust system leaks and isolators are correctly installed at all mounting points, what is not acceptable by industry standards, is when an exhaust system has been installed correctly, exiting well past the passenger compartment to have substantial exhaust sound transfer into the passenger compartment at a level which does not allow a person to talk without raising their voice to well above ambient noise levels. Whether you love to hear your engine roar (which I do), stereo blast or have a conversation, this interferes with your ability to enjoy what you like.

Now for the Causes

The first problem is most muffler shop staff today have little to no knowledge of exhaust systems, the “tricks” to installing a system that will “please” the customer, and simply verbally repeat the marketing materials provided to them by the system manufacturer. As previously noted by several others, there are 3 basic muffler designs, Absorption, Diffusion, and Chamber (Resonator), no matter which one suits your ear best, the criteria for promoting unnecessary in-cabin noise is the same.

Impactors:

Exhaust system material thickness should be no less than 16 gauge- double-walled pipe was commonly available through the 1970’s until manufacturers began seeking ways to reduce costs. Many of the “Muffler Chains” who marketed lifetime warranties always used double-walled pipe before “stainless steel” became the “in-crowd”. If a shop had it available, I would choose double-walled aluminized coated steel or 14 gauge stainless steel (depending on environmental conditions or personal tastes) - it is very quiet, solid and in terms of costs, pipe is pretty cheap, depending on length, 16 gauge aluminum coated runs about $11 to $20 wholesale (depending on diameter), stainless about double for the same gauge.

The muffler should be located as close to the axle (far away from the passenger compartment) as possible, allowing at least 3” of straight run pipe before a bend occurring (if installed to the forward position of the axle), with the overall length as long as possible. In the oem location, 24" will fit fine, located at the head pipe, 30" will fit fine as well and eliminate almost any possibility of drone in this particular location due to the size, length and insulation qualities (and yes, Allied does make units this long).

With regards to the 5.4/4.6 engines, The head-pipe (the pipe installed in between the exhaust manifold and the muffler) should be no greater in inside diameter the 2 7/8”, at 3” it now becomes a contributor.

Duel Tailpipes should be limited to no greater than 2.25” inside diameter, single tailpipes 3” maximum inside diameter- tips which are larger can certainly be installed but should be limited to 12” in length and have a discharge point past any material that may “catch” a sound wave or exhaust. When you exceed these diameters, it now becomes a contributor.

Tailpipe length in general should be as short as possible, minimal bends, etc, terminating past the axle, 1.5" past the body or bumper. Lengths greater than 4 feet promote “drone” (i.e. harmonics), typically about 3 ½ feet past the muffler.

Pipe diameter reduction should occur before the muffler. While many muffler installers like to use mufflers which reduce pipe diameter or split the exhaust at the point of discharge at the muffler, or install reducers to connect the tailpipes after the muffler induces “noise”.

Ultimately, it is the quality of the material and the installer which 90% of the time leads to a successful installation. I would like to also emphasize that it is not necessary to spend a fortune on a muffler ($100+) or system to have an excellent sounding, performing and long lasting result.


If you are looking for the least cost way out, I would install the longest Allied resonator(s), chance is the muffler has very poor insulation qualities, I'm guessing around 28" - 30" length will work very nicely. That will give a 90% chance of taking care of it- either single or duel set-up...doesn't matter. You can run a 3" diameter single and if you have duel tailpipes, the shop can fab up a wye off the back of the resonator.

 

I put a resonator on my 302 van years ago, nasty noisy droning thing. The cat was gutted, so I just bought a decent muffler and it restored the mid range and it was very quiet and no fuel mileage change either. Just put a pretty normal muffler on it.
Andrew

 

Please don't confuse a typical resonator with the Allied Unit. It used to be called a glasspack muffler in the 60's but as things changed, so did the name. It is constructed with the same methodology and quality of materials as Borla, Magnaflow, DynoMax, etc.

 

Exhaust and intake require a balance, why do people think bigger exhaust increases performance and mileage, it kills your torque, the engine needs some back pressure, the only time you want it opened up is if you have a turbo, it increases it's ability to spin faster by rushing air through it. The old round drum offset mufflers were great at keeping noise levels down, a stock engine benefits nothing with toying with the exhaust, if you can't increase the intake of air, no point in trying to increase the exhaust. My 99 had a big long cylindrical canister called a resonator mid van, then the muffler after it before going over the axle and out the side. I bet you just got a cheap stamped matted muffler, somewhat similar to the stock one, and if you increased the pipe size, that minus the cat has made it louder.

 

Update, i took it back to the muffler shop and got a resonator put on between the flange behind the downpipe and the muffler. It's still a little louder than i would like on the highway, but pretty quiet now at idle and since i put a higher flowing air filter on it, it seems a lot stronger. I'll have to hook up the Airstream soon and see how it pulls now but i guess i found the best balance between cost and noise. Still, if this helps anyone, i still think stock is best. If i could find a complete system at a salvage yard in good shape, i'd probably put it all back, but i'm sick of throwing money at this thing, i probably won't drive it more than a few thousand miles a year anyway.

 

well , that is the key... the best set-up for the amount of money you need to spend...Monitor the MPG and if it is worse or if truck feels sluggish you might need to change or upgrade the Mass Air Sensor since you are sucking more air now..

 

is that an easy upgrade? I need to learn more about it, i've changed intake/exhaust on lots of vehicles before and never touched the MAF.
thanks

 

The 97-up has a silencer in the intake that leads to the throttle body, I had a friend pull the intake, I removed the silencer that was in it, it necks down the size to about an 1 1/2", it's to limit suction noise, but restrict airflow, I found no noise, but a faint throttle response at WO for passing. Early injected vans do not have mass air, they are speed density.