Plumbing a fuel system

Whatever you do, plumb the system for return line and use it.

Buy a QUALITY return style regulator. The big Mallory 4 port was the best but you can only find them used any more. I have one.

With the pumps you have you can probably use the smaller Mallory bypass regulator and be fine.

No smaller than -10 from the tank to the pump(s). These pumps are designed to push, not suck. So any restriction to the pump(s) is bad. -12 is better if you are nearing 800 hp or more.

No smaller than -8 from the pump to the carb(s). -10 is better.

Set your fuel pressure at 5.0-5.5 psi. That’s all the pressure you need.

If you are going to use your Holley pumps, I would take them apart, pull the spring out of the bypass and using small plastic tubing you can buy about anywhere, replace the spring with the tube.

You don’t want a bypass at the pump and at the regulator.

With the bypass in the pump blocked off and a -8 line going forward you’ll have about 24-26 psi going up. That’s all they’ll make. If you use a -10 line it will drop it to about 20 psi.

I never use bigger than -6 from the regulator to the carb(s). There is no need for a -8 line there, but it doesn’t hurt anything. It’s just not needed.

That’s about all I can think of for now.

There is no way I’d do a fuel system today without a bypass. And I started using a bypass in 1984.

I was ridiculed horribly for it. It works.