1/8 inch. One loop is all that is necessary, but I'm not the resto resourch here, so that is just my .02 worth. If you want a gauge that has a more accurate read on oil pressure, change the line to 1/4 inch. You can see every small change in pressure with this setup, drives you nuts when it idles. Auto Meter was one of the first to offer this option.
------------------
Wally
Gold #67
67 Malibu "Small Block"
90 SS454
71 Malibu "Small Block"
93 torch red vette
------------------
Wally
Gold #67
67 Malibu "Small Block"
90 SS454
71 Malibu "Small Block"
93 torch red vette
