Have you looked through your audio manuals or contacted the manufactures on the current draw for your amplifiers and head-unit? Add those up, along with about 60amps for the vehicle applications, to see if 180-200amps at idle is enough without dropping the current?
Someone told me about the 60amps are needed for the vehicle so do not quote me…
Just in case, I make sure no accessories are running; i.e. A/C, heat, and head/running lights. Neutral and a little gas pedal for some higher RPMs will produce some more power. This is why I’m skeptical about upgrading my exhaust system.