Bypass vs Deadhead fuel pressure regulator question.

MileHighDart said

So cant decide if I want or need a return line in my new system.
Going to run new 3/8 hardline from my new 3/8" pickup in tank to engine bay, add a regulator and gauge.

Engine is a freshly rebuilt, basically stock 5.9, with airgap and eddy 1406, dougs headers. The electric pump I have is a carter rotary vane P4070 which I think is the 4-8 psi pump.

Was reading on another forum, some guy said you cant use a bypass regulator with that pump because it has a bypass built into the pump. Don't know if that's right or not.

Basically I want to get some parts ordered so I can get this done.
So wondering, can I use a bypass type regulator and plug the bypass, in case I want to add a return like later? Or should I just get a deadhead type, and worry about the return later if I have vapor lock issues or something.

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Unless you are going to 60 foot quicker than 1.40ish you don't need a return line.

Back in the early 1980's I used to block off the internal bypass in the Holley blue pumps and ran a number 8 high speed bypass valve back to the tank. The real is the weight of the fuel in the fuel line. A 3/8 line has more fuel by weight and volume as the same length of 5/16 line. A 1/2 has more weight and volume that the 3/8 line. As the line from the pump to the carb gets bigger, you have to overcome the weight of the fuel in the line, or it will stand off. Meaning you can have pressure on the gauge but no fuel moving in the line.

The only way to overcome that is by raising the line pressure. IIRC, those blue pumps were said to have a 15 pound spring in them. Of all I tested, most were actually 10-12 pounds. I would block the internal by pass and set the line pressure to 25 pounds.

The Holley engineers didn't like it, but it was easier on the pumps and stop fuel stand off in the line.