Drone Fixed! V6 Convertible w/ aftermarket mufflers

[Andrew@Lethal]

As many of you know, my journey to quell the drone after adding Magnaflow 11365 Mufflers (4x8" oval x 11" L straight thru) has been a long one. After having gone back to stock since last summer, I decided to try making branch resonators and giving them a try. I only wanted a moderately louder exhaust note, but stock was just too quiet. Up front, I want to thank Zackmd1 for his ideas and guidance last summer. Also big thanks to UglyJohn for not only sharing his learning down this road, but for most generously sharing the Excel spread sheets he had created showing the lengths required for differing rpm range drones.

So much information and I know I'll forget to mention a lot, but I'll post lots of pictures as well as sound videos (stock as well as MF 11365's w/ & w/o the new resonators) just so you can hear back to back. My muffler/ sound level preference is not 'Attack' or muffler delete loud, but more subtle. I am very happy with my exhaust sound, but I know it would be too tame for many. Viva la difference! ;)

I can share more detail later if desired (God knows I went into the minutia), just ask if you have any questions.


Before: (w/ Magnaflow 11365's)

Rear view: two 45" long 2.25" branch resonators w/ mandrel bend 180º's (4" CL radius) and very nice Borla double wall tips to finish.

Stealth look from the back. resonators not visible.

A view from passenger side showing resonator curving up behind the rear valance. I used three band clamps per side because the resonators were designed to be adjustable from ≈ 40" to 50" and to be removable from the stub I had welded into the main exh. pipe. Turns out my 45" 'flow length' worked out better than I could have hoped for, so I did no adjusting!

A view of the branch resonator tube w/o the muffler. The top of the resonator has about 3/8" to 1/2" clearance between the cross member, the frame rail and the spare tire sump, so I partially wraapped w/ 3/8" thick black pipe insulation to insure it would not come in contact with any of those surfaces. I wanted to keep the mufflers removable, so the saddle clamp is tack welded to the main tail pipe. the hanger bracket seen above mounts with a 1 1/4" band clamp at the back of the muffler because it is off center and wants to rotate w/o it.

***The secret to making this adjustable was finding tubing that had and i.d. that snugly slipped over 2 1/4" (o.d.) exhaust pipe. Turns out that galvanized fence post from Home Depot was a sung fit, but with sanding the interior seam a bit, it slipped right on (w/ help of WD-40 too).


A close up of the rear end of the resonator. It is secured with a heavy duty rubber hanger strap that the 3/8" muffler hanger prong goes thru (into the oem isolator above valance) while it's other end is bolted to an 'L' bracket secured to the trunk sump. A saddle claamp aattaches the resonator to the rubber strap.

A look at how the resonator fits above xmember and between frame and spare tire sump. At the left you can just see the end of the other end of the rubber strap that the muffler prong goes thru (then into the oem isolator).

A view from in front of the muffler looking back. The yellow stuff in the frame rail and xmember is that expanding household foam I had used last summer to try to deaden the resonance/drone from the mufflers transferring to the body (made ZERO difference :headbonk. And the cardboard you may notice above the xmember (above photo) was to confine the foam to the xmember.

Another angle of the whole assembly.

Thanks to UglyJohn for these charts that give the needed resonator lengths given where your drone range is centered and it's associated frequency (Hz) at various average temperatures inside your res. tube.
The average exterior temp of my res tube on a 72º day was ≈ 100ºf.
[note: The formula used for these charts are based on 6 cylinders! At any given RPM range/ freq., the length needed for a V8 would be much shorter] My drone range was lower in the rpm range than most others, meaning my res. tube needed to be longer than most, hence the 45" for my situation.

Here is the chart for a V6 in the 1000 - 1700 rpm centered range.

Here is the chart for a V6 with drone centered at 1800 - 2500 rpms:

And for the final touch, the sound videos, I'll put them in post #2

:cheers:

Thanks,
Dave

Great work, glad you got your car exactly how you wanted it to sound!

Sponsored