Test pipes are louder than cats and loudness ,as stated before, is relative. In my experience with test pipes the sound is just one concern. It seems a tune is necessary address the O2 sensors. Even with J-bungs my car did not run well before the tune and occasionally I still get a CEL from the cats not being there and the O2 sensors not registering enough of a change in the exhaust gases and upsets the ECU. I believe this would be an issue with any mod that removes cats. I think ,IMHO, high flow cats are a good compromise or even resonated test pipes if you are concerned about volume but be aware of the possibility that the O2 sensors may not be happy.
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'14 Nismo AAM 3" TD / AAM Test pipes / AAM CAI / Lowered on Swift / Synolimit Ported TB, upper and lower manifold /DW 1000cc injectors and 340 pump / ECUtek tuned by Hal @ Dynosty / 331whp/268wtq on E85
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