Has this exhaust been modded?

[tadmcmichael]

Originally Posted by JsL

The OEM muffler has four chambers total: 2 helmholtz chambers and 2 resonator/absorption chambers.

Helmholtz chambers help with drone and volume and resonator chambers help with volume and rasp.

ACM mod bypasses all four chambers. "OEM Mod" or perforated pipe mod bypasses the two resonator chambers, but leaves the two helmholtz chambers alone. See diagram from Dinan's website.

Thanks JSL, that explains it well. So rasp, drone, and loudness should be exactly the same between the ACM mod I have now and straight pipes? There isn't really any gasses escaping to the muffler itself?

[s85e90]

Originally Posted by JsL

The OEM muffler has four chambers total: 2 helmholtz chambers and 2 resonator/absorption chambers.

Helmholtz chambers help with drone and volume and resonator chambers help with volume and rasp.

ACM mod bypasses all four chambers. "OEM Mod" or perforated pipe mod bypasses the two resonator chambers, but leaves the two helmholtz chambers alone. See diagram from Dinan's website.

Helmholtz chambers length must be tuned for the sound output. Once the muffler is modded, the factory chambers DO NOTHING AT ALL.

[JsL]

Originally Posted by s85e90

Helmholtz chambers length must be tuned for the sound output. Once the muffler is modded, the factory chambers DO NOTHING AT ALL.

I agree that the chamber length must be tuned to a certain frequency.

The OEM mod has stockish level of drone with an increase in volume. I think the helmholtz chambers, which are untouched in the oem mod, are still working.