Hi,
I am flying a flight from dfw-sju when i look at flightaware.com is shows the filed speed as 451 kts and the plane is going 481 kts. Well on fsx the red bar up top shows that i am going 348 and that is with throttles open. How can i raise the max speed of the 757 so that it matches the speed that the real one is going?  

Indicated airspeed is dependant on outside airpressure that changes with altitude. It does not indicate speed over ground. Your speed over the ground is significantly more than that indicated at altitude.