I understand that on a dynojet chart, graph,etc., that there is a column for horse power and torque. But why are there two lines on the graph? For example look at the topic "NEW VIPER" by the threadstarter "ALLVENOM."

 

one line is the torque curve and the other line is the HP curve. they always intersect at 5,252 rpm too.
the torque curve usually reaches its peak at a lower rpm than the HP curve does so this is one way to tell which is which.

 

One line is hp, one line is tq, the curvy line at the bottom is the air/fuel ratio, the red line at the bottom is most likely his ideal air/fuel ratio. Air/fuel is used to tell if the car is running rich or lean. Too much gas or not enough.