Originally Posted by downwardspiral

I'm almost positive that a boost gauge on a naturally aspirated car's intake tube would read 0 psi (maybe a fractional increase, but nothing worth looking at) no matter how it is positioned. As you mentioned, there is a vacuum inside the engine, which as you said is a giant air pump... that's the only real pressure difference. If you held a pipe with a ballon duct taped to one end out the window, it would not fill up the balloon.. The air would occupy the balloon until the point that it needs to be compressed, then "new air" would flow around the contraption.. The pipe might fly out of your hand because the air is at a higher velocity relative to the pipe. Having a large pipe with a small hole on the end is a nozzle.. that's a different story than ram air. Air will not compress itself.