Go to 14th post on page 4 and you find some stuff.
I have no clue if those times are good or not, but i see dragging in gt5 as "street drag", where the car that comes to a certain distance before the other wins (if both launch at the same time of course)
I put the map to the highest, and going up slowly to the start line, on that highway track in practice mode. the counter starts when U pass the line, after dragging I check the time and speed in the data logger... thats all