You should get a full second off your ET. Let me run down what 2 guys are doing in my bracket class.
'05 GT Auto, DR's, 3.73, CAI/ SCT tune (not a custom/mail order) tune. UDP's, CMDP. He ran 13.9x before the N20. with a 75 shot he's running 12.8-12.9.
'07 GT Auto, DR's, 3.73, CAI/ Predator...