Per my V-AFC, the highest intake pressure that I've seen is -0.5psi. I think that this can probably be increased to around -0.2 psi, but I need to run the calculations. As an HVAC designer, I can calculate what will happen to the airflow, but I've been lazy about it. Jim, good ideas for testing ..... I didn't think of it.

 

I ran the calcs assuming that my CAI with the smooth elbow equates to 15 equivalent feet (5 feet actual plus 10 for the elbow).

3.0L engine @ 6200 rpm, intake =3.5"dia.

friction loss = 0.198 psi

Pretty close to my guess!!!