What gives a car a awesome sound while it shifts kinda like on fast and furious?

Answer 1

You are probably hearing the blow off valve (BOV) used on turbocharged engines. The blow off valve releases excess turbo pressure when the throttle is lifted (such as you do when you shift). Some blow off valves vent back into the intake system and are virtually silent while others just vent out into the air which makes a flutter/whistle sound depending on the valve. Putting a BOV that vents to the air on a car originally equipped and tuned for a BOV that vents back into the intake can affect the mixture in off throttle situations causing the engine to run too rich and even stall as a result. There are hybrid BOVs that do both and allow you to adjust that ratio of blow off that is vented out and how much is returned to the intake so that you can achieve the BOV sound while maintaining sufficient returns to the intake.