Air flowing through a 4 inch pipe
At 60 mph. creates how much psi.

It's not that simple - the pressure in the pipe is dependent on the density of the air as well as its velocity. If you can tell us the pressure or density of the air at 0 mph then you can use Bernoulli's equation to find the decrease in pressure from ambient for when its moving at 60 mph:


\frac {v^2} 2 + \frac p {\rho} + gh = constant


From this you get:


p_2 = p_1 - \frac {\rho v^2} 2


where p_1 = ambient pressure, p_2 = pressure at 60 mph, and \rho = air density.

ebaines: You're quicker on the draw today than me. :)