need some advice, running 3/8" fuel line, how to run, what to use

space duster 383 said
I r

an 3/8 SS, not once but twice. The bends didn't get me, the double flares did. I highly recommend not using SS if you have to do your own flares. I went through two flare kits trying to get a double flare I could trust. Finally went with SS braided from Holley up from the mechanical pump to the area in front of the water pump. From there it is all aluminum fittings from Summit and some from Holley. I put a Holley filter in the line from the water pump area to the double pumper dual feed with a fuel pressure gauge. I'm satisfied with my set up, but I nearly had a serious problem with a SS flare leaking over the intake manifold and the pan. My fault, not the material's, but don't take short cuts with the SS line if you use it.

Those cute little flare kits are just about impossible to use for anything stainless and even standard materials for tube larger than 5/16". I gave up on those and bought one of these
Professional Brake Tubing Flaring Tool - Eastwood

Yeah, it's expensive. But it works every single time, does 3/8" stainless no problem. And I've already used mine enough to make it worthwhile. I usually buy the full length prebent fuel lines just because of how long they are and how many bends they have, but I make a lot of my brake lines because bending/routing them is pretty easy.