IASCA places the mic 4" from the glass at a certain height.(can't remember right now) and I believe USAC places the mic generally where the listener's head would be. I can think of no Sanctioning body that places the mic UNDER the dash. There is no logical reason(other than boosting SPL numbers) for placing the mic down there. Given 2 12's, 400 watts and the interior volume of a Z I would agree with SLOTH saying mid to low 130'sDB. I personally hit 141.1DB with 2 JBL 12's 600watts(rockford fosgate) in an old Nissan Sentra(smaller interior) but that was IASCA and I used Flashdance with an Audio Control SPL meter. The box and car was tuned for SPL and Flashdance "tricks" the Audio Control SPL meter.