im turboing my 400 in my dart and the turbo mustang site i hang out on, most of them restrict their oil feed. they like to use jet sizes as a comparision and some run as small as a #60 holley jet. thats small, i think too small unless its a ball bearing turbo. id venture to say anything from 1/16"-1/8" would be fine for a restriction. i am also using -10 AN line for my return line. it is approx 5/8" inside diameter.

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74 swinger slant 6, the slowest, most fun car i have ever owned.

225 Dart, it somewhat comforting to think Jeff is not completely alone in his practice of restricting the oil one. What I am thinking here now, is that this practice might be appropriate only for ball bearing turbos. If Buick has a 1/4" line, and got good service out of their turbo units, then maybe there is a reason for that. I don;t know, just wondering out ound here now. Since the Buick unit has some sort of sleeve bearing, then maybe a higher quantity of oil is needed to cool the bearing.

I have already installed a 1/4" brake line for the oil feed. It would be easy to restrict that if I thougth it wise to do so later. I will be sure to use oil resistant hose for the return. One advantage of putting the return fitting in the block is that since the block is SLANTED, the barb tilts up, and thus offers a continual downward path for the oil to run down.

If everyone out there is using a #10, or 5/8" return hose with no problems, then I will just make sure there are no restrictions in my set up, and use the same. I'm pretty sure the 5/8" heater hose barb I have installed in the block has no restrictions in its inner diameter. Even though it threads into a 3/8" NPT thread, the ID is the same all the way through. The heater barb is steel, and thin-walled, so perhaps the steel offers less retriction than a brass fitting. Anyway, I will check it out carefully, and thank you all for your guidance.