What size fuel lines is a good size for the lines from the splitter to the heads and for the return lines? Is 3/8's okay? I will be using hard line. I ask because if can get a splitter (fuel Y) that has the same inlets and outlets it would eliminate the need for multiple adapters...

 

I assume 3/8's is since thats what the stock is.

 

3/8 is plenty big Rob. I run -4an braided lines.

 

Alright, thanks. I think ill stick with NPT fittings instead of AN fittings, mainly because I'm more familiar with the sizing and it'll make parts store runs easy lol.

 

3/8" is fine. The stock return is 5/16" though so you're going to have to adapt at your reg to 3/8" ins and 5/16" out or replace the return line all the way back.

 

Yah I'll probably Just do a 3/8 to 5/16 adapter at the outlet side of the regulator.

 

Don't forget about JIC flares too. They're pretty much like AN fittings but the machining tolerances are just not quite so incredibly precise and they come in SAE sizing that you're familiar with. Like the fuel lines that go from the heads to the stock FPR are 1/4" 37* flares.

Edit: oops

 

Ill look into those. Probably do a little better than NPT threads

 

-4 or 1/4 lines is what goes from the banjo bolt to the heads and from the heads to the regulator on a stock truck. I used -5 or 5/16 lines because I thought 3/8 where too big, specially the fittings. JIC fittings are same thread as AN too so they are more compact. Only thing I will say is availability of -5 fittings compared to -4 or -6 is they are hard to find. I ordered all of them online so I found lot's of options, it wasn't until I was working on my truck and was missing an adapter that I found it impossible to find -5 JIC fittings or adapters locally. something to keep in mind too. The other sizes are much more common