How much horsepower would an 02 mustang gt with a cold air intake and high performance chip have?

A 2002 Mustang GT with just a cold air intake and a performance chip will see a modest horsepower increase, but not a dramatic one. You're unlikely to see more than a 15-20 horsepower gain at the wheels.

Stock, a 2002 Mustang GT makes approximately 260 horsepower at the crank. Aftermarket parts are often advertised with "crank horsepower" gains, which is the power measured at the engine itself, but what matters more is the "wheel horsepower," which is the power actually delivered to the wheels after accounting for drivetrain losses.

Considering the wheel horsepower loss in a Mustang's drivetrain, a realistic estimate of the increase with those modifications would be around 275-285 wheel horsepower. This is a rough estimate, and the actual increase will vary based on the specific cold air intake and chip used, as well as the condition of the engine and the accuracy of the dyno used for measurement.