I have a mild cruise rpm drone that I would like to work on tuning out of my exhaust system. I am running about 70mph at 2,000rpm where I notice it most.

There is real estate after the mufflers and before the tips to either add traditional inline resonators, or add j-pipes and try to tune in helmholtz style resonators.


Have you done either style resonator? How were the results?

Goody,
Member Sunroofcuda made a set of resonators for my Challenger out of 2.5" in that same area. No drone!

The Challenger may have a couple more inches of space than the Cuda though.

I did the helmholz style and that worked great. My drone was from 40-48 mph. Had a 2.94 gear so that made you stay in the drone zone longer. It was completely eliminated. But I would do the resonators if they did the same job. Cleaner look.

When I installed headers I removed the helmholz pipes also and I had no drone. Stock manifolds seemed to enhance the drone.

Those bullet resonators are pretty effective. On my 2000 BMW M5 I replaced the massive muffler system (four 9" diameter cans) with a pair of 12" SS resonators and the exhaust note is perfect with no drone at all.

Thanks, I'm tempted to try the helmholtz style because I want to focus on the right frequency. The off-the-shelf resonators just seem to be a shot in the dark on what rpm range you can expect it to function at.

The bullets (or as us old guys call them, glass packs) may be a shot in the dark, but they only cost about $20 a piece. And I have put them on about every street car that I have ever had and they always knocked the drone down completely or to a tolerable level. I have a pair on my Cuda with a 540 Hemi.They work very well.

I put a glass pack inline with a flow master 2 chamber on my Jeep. I am getting old so the stroker 4.0 was getting too loud to me with just the flow master . The glass pack/resonator/bullet put inline reduced the noise level nicely but didn't alter the sound at all. A friend of mine had a similar experience with a LS1 camaro years ago. Loved everything but the drone and volume level, adding a glass pack fixed both.

I'm going to buy the helmholtz style resonators and weld them in, I feel like I have the best shot with those to tune out the specific rpm range I'm after. I'll follow-up with the results.

Who has those? (just curious to see who you find ........)

Following up on this for those still interested.

I bought 24" NODrone helmholtz resonators from Synapseengineering [below]. Cut the ends off, used 45° bends and welded vacuum-actuated cutouts to the end.

When I'm not "on the throttle", they are shut and the resonators are working very well around 2,000rpm, where I had my issue. Moderate acceleration the cutouts open up and the car makes a little more noise.




Supporting info

J-tube Vendor
http://synapseengineering.com/synapseusa/products/nodrone.html?SID=76i1d7un3a55c1b9psfdog0eh7

Grassroots thread
https://grassrootsmotorsports.com/f...tor-or-helmholtz-resonator/129212/page1/

Calculation details
https://www.performancetrucks.net/f...t-resonator-tube-eliminate-drone-489463/

Vacuum cutouts
https://proflowexhaust.com/products/proflow-vacuum-actuated-exhaust-cutout-valve