Stop the Drone - Helmholtz Style

[MG]

Wait, so , why do you have drone again? Did you alter the exhaust to fix drone that was already present or did you get the drone because you altered the exhaust? Im curious because my L99 has no drone at all.

Currently contemplating a simple muffler delete or a full 3" StainlessWorks header-back exhaust.......

[Roger Ramjet]

The drone comes with some aftermarket exhaust systems, X-pipe installs, or muffler changes/deletes. L99s are fine with the factory center resonator in place - with or without mufflers.

[Hicompression]

Originally Posted by MG

...or did you get the drone because you altered the exhaust? Im curious because my L99 has no drone at all.

Yes. The factory L99 mufflers have Helmholtz chambers built into them. See my earlier post with a pic of the cut-away of an L99 muffler (page 1, post #10). When the stock mufflers are removed, aftermarket systems tend to have drone. Adding a Helmholtz chamber to an aftermarket exhaust system gets you back to what the car came with from the factory (except for a different appearance and different exhaust note).

[BigRed585Lbs]

EXACTLY the purpose of Roger's initial post! Just trying to offer a solution to people who bought expensive exhaust parts and came away with not being totally satisfied with their particular exhaust experience.

The "sound" is out there.

[zepcom]

Originally Posted by MG

Wait, so , why do you have drone again? Did you alter the exhaust to fix drone that was already present or did you get the drone because you altered the exhaust? Im curious because my L99 has no drone at all.

Currently contemplating a simple muffler delete or a full 3" StainlessWorks header-back exhaust.......

I believe that SSMike was saying that when he bought his SOLO Mach X, it was 100% drone free on his V8 M6 SS.

He recently upgraded to the SOLO High Flow Cats, which introduced a small spot where drone has appeared.

It is my understanding that he is starting to work with the owner of SOLO Performance to test out a J-bend solution on his V8 "Mach X" to compensate for his latest change to his exhaust system.

TL;DR: His exhaust was drone free until he added HF cats. Now he's going to test out a J-bend solution to fix this.

[ssmike]

I just had a conversation with Jeff at Solo and we decided that rather than go into designing and testing a j-pipe setup for my car, we would try a set of resonators first. The drone that I get is limited to certain conditions such as 4th or 5th gear around 55mph going uphil, working the engine. Highway cruising in 6th gear is not an issue. As zepcom said, I had NO drone whatsoever with just the Solo catback and shorty headers. When I added the high flow cats it got louder so along came some droning. Jeff feels confident that the resonators will smooth out the tone enough to help with the limited drone without affecting performance. He said they are high flow straight through resonators! Getting it done tomorrow so I'll post results.

[ssmike]

Got the resonators installed today! They helped cut the "edge" of the loudness and reduced some of the drone I was experiencing. I'll know more as I drive it in the next couple weeks. I really like the sound now, not as obnoxiously loud and more tolerable when cruising!

[BigRed585Lbs]

Boy, they do good work!!!! Bet it sounds sweet!

[Supercharged SS]

We added two 12" resonators to my Kooks 3" system and it hardly helped at all. The drone is still present at cruise, about 2k or low 70's. Take it up to 80 mph and its hardly noticeable.

[ZAPSSRS]

Is this in reference to the Kooks 3" full exhaust system?
This system has the mufflers so where do you install the resonators?

[Roger Ramjet]

Installing the J-pipes has made the exhaust system 2 or 3 dB quieter overall - most noticeable at idle. I suspect there is also some odd node harmonic attenuation within the pipe cancelling frequencies other than the trarget 120 Hz. The sound is pleasant, deep, and throaty as desired.

[Supercharged SS]

With the kooks 3" system we put the resonators after the cats and in front of the mufflers. It's a tight fit.

[4xchamp]

Originally Posted by Roger Ramjet

These pipes are 28 inches of 2.25 tubing. The result retains some growl up to about 1400 RPM then it just stops.

Roger , thank you for for innovating and sharing this with us .
The drone in my car could suck my brains out through my ears . I never cruise the car 1800 to 2200 rpm because of this .
I have two questions .
Does the pipe have to be a "J" or can it be straight ?
Do cam changes , and different bolt ons change the calculation for length/diameter ?
I'm definitely trying this this week . I was considering clamping on one section of the pipe to make it length adjustable so I may tune it to my mods .
Do you feel this is worthwile or should I fab and install the 28 x 2.25 pipe ?
Thanks again for thinking outside the box . I'm positive there are numerous enthusiasts that will benefit .

[Roger Ramjet]

The length is critical - diameter, not so much. Can be ANY shape.
Yes, I would recommend that you make the pipe adjustable. Start at maybe 36" then shorten until you hit the offending frequency.