Quote:
Originally Posted by tadmcmichael
Why is the ACM so much louder than the perf? If the ACM are equivalent to straight pipes, seems like the perf is also straight pipes although they cross?
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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.