i think the mopar vapor separator is a fairly ingenious part. it filtered and eliminated the vapors, but it's at it's best when matched to the proper fuel pump. the 3-5lb big block pumps were miserable pieces. i remember fighting the vapor lock problem with a 383. it seemed the problem really raised it's ugly head at the track when folks were idling in the staging lanes. i did all kinds of silly things to cure the problem. eventually (sometime in 1968) i switched to a street hemi pump and never noticed any more vapor lock problems (i didn't do a return/vapor separator). but, the high pressure street hemi pump by itself set me up for other problems. all this works the best when parts are matched together..