Actually, it's not sufficient to match the intake air speed, which isn't constant anyway.
You need to be going fast enough to make dynamic pressure, which is easy enough to calculate.
It's 1/2 * (air density) * (net airspeed)**2
The net airspeed is the difference between how fast you are going in still air and the intake airspeed.
If you want 10 PSI boost with the engine OFF, you need an airspeed of 340 m/s at 20 deg C, which is DANG close to the speed of sound at sea level. With the engine running at peak power, the intake velocity in an ideally designed engine approaches (but doesn't exceed) the speed of sound itself, so you need a vehicle that goes near Mach 2 to get 10 PSI boost.