Originally posted by dr_bowtie
C9x.....

wrong answer......

hook a vacuum gauge to full then ported vacuum and see what you get...

One will have vacuum at idle then decrease when quickly opening the throttle....

while the other will have no vacuum at idle and increase while opening the throttle....


The answer I gave is correct.

Running a fairly well matched pair of vacuum gauges - which I've done - on an engine shows zero or near zero vacuum from both ported and manifold vacuum when the throttle is wide open.

Part throttle operation does show differences, but wide open throttle shows zero regardless of vacuum source.