DIY Hemlholtz Resonator

[chamolm]

I have a GMPP muffler on my 2010 Camaro SS and I am pretty sensitive to noise. I liked the volume level of this muffler but the system had resonance right around highway speeds.

I read some academic papers and came up with a Helmholtz resonator that fit with my trailer hitch receiver. It's pretty large because I wanted it to have a large bandwidth of attenuation and cover the whole cruising RPM range. I used 0.065" wall, ASTM A312 TP304 tubing for this and the mass was 2.1-kg/side. The stock was 9.2-kg/side and the GMPP muffler is 3.4-kg/side so still lighter than stock overall. Also lighter than a 36" long, 0.065" wall, 2.5" OD J-pipe which I estimate at 2.4-kg/side.

Welded it up at work and I'm pleased to say that it's mostly a success! I was targeting a 102-Hz resonant frequency and a total bandwidth (using a 3dB minimum attenuation band) of 80-Hz. I don't have a scientific way to validate but it sounds like it's working from 1200-rpm to 1900-rpm. So it ultimately serves the purpose I intended. It also stops working above around 2000-rpm so there's no impediment to the good noises.

Just wanted to post this as I don't think I've seen this solution done as a DIY before.

[InFiD3ViL]

Damn man, nice work! And with mini v-band connection?

Oh yeah, and welcome to Camaro5!!!

[The SS Godfather]

Originally Posted by chamolm

I have a GMPP muffler on my 2010 Camaro SS and I am pretty sensitive to noise. I liked the volume level of this muffler but the system had resonance right around highway speeds.

I read some academic papers and came up with a Helmholtz resonator that fit with my trailer hitch receiver. It's pretty large because I wanted it to have a large bandwidth of attenuation and cover the whole cruising RPM range. I used 0.065" wall, ASTM A312 TP304 tubing for this and the mass was 2.1-kg/side. The stock was 9.2-kg/side and the GMPP muffler is 3.4-kg/side so still lighter than stock overall. Also lighter than a 36" long, 0.065" wall, 2.5" OD J-pipe which I estimate at 2.4-kg/side.

Welded it up at work and I'm pleased to say that it's mostly a success! I was targeting a 102-Hz resonant frequency and a total bandwidth (using a 3dB minimum attenuation band) of 80-Hz. I don't have a scientific way to validate but it sounds like it's working from 1200-rpm to 1900-rpm. So it ultimately serves the purpose I intended. It also stops working above around 2000-rpm so there's no impediment to the good noises.

Just wanted to post this as I don't think I've seen this solution done as a DIY before.

Well smart and tidy idea keeping noise down
Ha ha you would hate mine, no cats straight pipes to electric cuts outs... old photo shows cats but cuts... WELCOME BTW

[chamolm]

Originally Posted by InFiD3ViL

Damn man, nice work! And with mini v-band connection?

Oh yeah, and welcome to Camaro5!!!

InFiD3ViL, thanks! This is actually an ASME BPE sanitary ferrule connection. Usually these have a hand knob for tightening — I swapped that out with a Nylock and torqued to 50% yield strength. I have my doubts as to whether it'll snap or not so I welded a washer to the back end of the resonator to give myself a loop and safety wired to the exhaust hanger. So at least if it snaps it won't go flying down the road.


They do make high pressure versions of this clamp with two bolts instead of a pivot and I could use that if it snaps. They come with torque specs and some measure of assurance it'll hold it.