Quote:
Originally Posted by J.Jensen
Thanks for posting more images 
How much speed do you need to overcome the engines air consumption and start building pressure? |
You are welcome, but be warned that the answer will start another debate.
Pressure is all relative. When you use pressure readings taken at the airbox as reference, you will begin building pressure at pretty much anything above idle, even without forward motion. The reason for this is the nature of a divergent system. At the risk of oversimplification, the divergence will cause the higher velocity air at the inlet to begin "packing" the air as it slows. Also think Bernoulli's principal, as the air velocity decreases, it's pressure will increase. On a proper divergent ram air system, the combination of these two forces will result in a "less vacuum" reading as compared to no system at all, which can be counted as a pressure increase.
Without counting the effectiveness of the divergent system, pure ram air will net ABOUT 1.2psi at 200mph.