So a feller I work with researched this forum and decided a magnaflow muffler was the way to go...



He's gotlong tube headers, high flow cats, dual 2.5 inch mid pipes to a SI/SO 3 inch diameter pipe (24 inch oval body muffler) the exhaust ends right after the muffler (about 6 inches in front of the axle). The truck has a decent note/tone but minimal volume outside the truck and the usual rasp at higher rpms from magnaflow mufflers and a HUGE ISSUE



This truck resonates so bad in the cab he's ready to go to long tube headers and nothing else...





I suggested he at least install an elbow to install on the back of the muffler BUT he's not sure it will help. Anyone have anyother ideas????

 

Send the exhaust out the back. The noise is from resonance (drone) is the sound between the ground and truck. I have the Magnaflow Tru-X 11 inch oval body DI/DO and mine isn't to bad. I turn up the stereo on the highway and I don't notice it at all. Here is a pick for reference. MagnaFlow Mufflers - MF14379

 

due to suspension mods, he can't run it out the back...

 

Dual midpipes to a 3" single? Interesting..

If he cant run it lightning style even, switch to a large Borla Pro-XS, or add big round bodies and a resonated tip under the truck.

 

Well, at least turn the exhaust out the side(s). Dumping it out under the truck will always make it loud inside the cab, due to the resonance of sound waves bouncing around under there.. Always has, always will.

 

Pro XS is out on this deal. He already has a 24" maggie. The largest Pro XS is a 19" body.

I suggest first off, run tips out back! Then, if we still need it quieter, add a magnapack in front of the 24" muffler.

 

I thought Pro-XS was available in 24" also. Hmm.

According to Tarajerame,

 

yup, tips out the back is a "NO GO" due to suspension mods


I'm sure he's going to end up running a Lightning style exit, he's tight for money and I'm hoping the turn down will be a cheap temp "fix" and at least have the truck bearable to drive...



it's not a constant drone, just on hills and when it's normall gentle driving at anything over 1300 RPMS



at WOT it's got a decent sound and minimal noise in the cab

 

If you do a straight down turn down it will be as bad or worse. If you go with the elbow that you mentioned earlier then point it to the side with a clear shot to outside. The sound will bounce if the pipe is aimed at anything under the truck (A.K.A. drone). I think a 45* would work better than a 90* also.

But what do I know? MHO.

 

I'll ensure I let him know as I suggested cutting the Magnaflow off and adding a Flowmaster 50 series

 

^ I sure hope not! haha

 

If he has to keep the dump, put a 2.5" core straight thru glasspack like a Cherrybomb or Thrush or whatever, in EACH of the twin 2.5" mid pipes.

A turn down dump undreneath certainly amplifies any drone as soundwaves reflect back off the roadway and under body. As long as that stays, he's going to have some drone with his setup, even if he does add the glasspack "resonators" I mention above.

 

FLOW-MASTERS? He might as well go back to stock before he makes that mistake. *Sighs*!

 

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.

 

so my buddy installed this magnaslow in place of a Flowmaster and I assure you it's the last magnaslow he'll ever install and I threw my magnaflow muffler in the dumpster VS trying to continue to sell it to some poor sap