Quarter mile times will vary by a large amount according to how well the car is set up, the driver, the track, the air quality, etc. The time can be from high 12 sec to mid 14 sec. Here is a link to a COPO shootout were a 1970 COPO LT1 Nova ran 12.9 sec.
http://www.d-p-g.com/musclecar/CurrentIssue/eJ.htm