Attached is an article from sport rider on some ram air tests on several high-performance bikes. The peak boost from the ram was about 25 mbar, or about 0.4 psi, at 180 mph. The theoretical equation would give about 0.6 psi at 180 mph. We have tested hundreds of ram air intakes in wind tunnels and the boost is seldom, if ever, greater than what the theory predicts. However, if the wave dynamics in the ram air duct reinforce the wave dynamics in the engine's air induction system, there could be a significant increase in boost at some engine speeds. This is seen in the European Comprex supercharger, the pulse jet engine ( the V-1 buzz bomb of WW 2), or the pulse detonation engine that has seen a lot of press in recent years.
Sport Rider article If someone has some data that shows different results I would love to see it. I've been doing this work with jet engines for over forty years in the aerospace industry, but I never cease to be amazed and surprised by the inventiveness, ingenuity, and the ability to just "know what works" that most hot rodders have. I wish that a lot of the engineers that I work with were as good with engines.
