WVO fuel line size
 

Just out of curiousity.....what size fuel line would you recommend for WVO supply and return lines. I'm thinking 3/8" or 1/2", or would that be too large?

Ultimately, you're going to be limited by the size of the fuel line "plumbing" on the lift pump and injection pump. So, unless you are planning on also upsizing all of that it make no benefit in having larger than stock fuel lines for the WVO.

Hmmm, never thought of that angle. You are correct, the size of the plumbing on the IP and lift pump are going to be the restriction point in the whole thing

Pex Line
 

I usually use PEX line for fuel line. I get 3/8 OD with 1/4 ID The only place I do not use it is on the in to the fuel pump because it is designed for the rubber hose to attach to the pre filter. For that piece I use a 2" stub with fitting and have the pex attached to that. The stub gets attached with hose clamp.

The reason for this is no hose clamps which are extreme weak spots on WVO conversions. The factory fuel line for the filter connection and IP connection is plastic tubing. And it works the same way. I heat the PEX and push it on the factory fittings and it shrink wraps itself to the fittings. If you are ever worried about rubbing it I install heater hose over the PEX line as a protection.

Untrue. The head losses (pressure loss) due to piping are typically a lot more than the losses due to fitting, restrictions, etc. You can always step down. In the trade, fitting & valve losses are typically called the 'minor losses'. Engineeringtoolbox has some hydraulic rules & formulas summarized, otherwise, hit up a fluids textbook, or mechanical engineers handbook. That being said, my system came to me w/ 1/4" or 5/16" copper tubing for the fuel line, but it's a single line looped system. The bundle of black snakes under the hood is 5/16" fuel line. I'd go w/ 3/8" line to the tank for a 2 line unlooped system (VO pumps from and returns to tank at all times).

Fuel line
 

I have used 3/8 ID PEX on a few conversions (my wife's Jeep CRD) the hard part is finding it longer than 10 feet without having to pay shipping. I have run 1/2 ID Pex line as all the lines. The coolant to and from the tank the fuel to and from the tank. I did two down one side of the car and two down the other side. It was on a 1995 S350 turbo diesel and the hoses ran inside the door sills, and the fender liners. It was not my car but I had done a 1993 of the same body style and the 95 with all PEX was sharp.

Does copper corrode in WVO?

I used 1/4" ID lines on my setup and they worked out fine

I went with 3/8 thru to heat exchanger,then went down to fuel line size,or course I used a pusher fuel pump.