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.
67 Malibu "Small Block"
71 Malibu "Small Block"
93 torch red vette
A forum community dedicated to Chevrolet Chevelle owners and enthusiasts. Come join the discussion about restorations, builds, performance, modifications, classifieds, troubleshooting, maintenance, and more!