Situation: Created custom fuel rail, now i need to plumb the system.

Question: Can I run Just a feed line to the fuel rail if I use a Bypass Style Fuel Pressure Regulator?

Never mind. I just read your thing about the C70 setup, so apparently Volvo figured it out one way or the other...
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Justin 66 122E
Read vclassics tech!

They can do it on modern cars because the modern ECU has enough computing power to measure the instantanious fuel pressure and adjust the injector pulse in real time.

Fuel pressure and fuel volume are two different things. The FPR addresses both when placed on the fuel rail. Think of your proposition like a garden hose. Pressure just behind your spray nozzle (or fuel injector) is greater when the nozzle is closed than when it's opened. It also varied with how wide the sprayer is open. The pressure at the sprayer isn't regulated and, because the potential volume is regulated upstream of the sprayer, pressure is variable. Think of how you can spray water further when you first squeeze the nozzle as compared to letting it run and then aiming for your target, such as that far off flower bed.

You could get fancy and determine the fuel demand at all possible engine speeds and throttle positions and calibrate a regulator to allow the exact amount of fuel through necessary to maintain the proper pressure, however. I think a rising rate FPR takes this sort of approach, using manifold vacuum as a signal, but I'm not very familiar with those.
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Justin 66 122E
Read vclassics tech!

If you do it that way it may take a long time to bleed the air out if it
becomes empty somehow. With the reg up front it bleeds back through the
bypass.
Diesels are set up this way and on many of them if they run out of fuel you
have to bleed them more or less like you bleed brakes.
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George Downs Bartlesville, Heart of the USA!

I didn't think of that. I wonder if vapor locking would be more of an issue too.

See George, you've become a real D-jet kind of guy.
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Chris - 1990 740, 1973 1800ES (Non-running), 1993 Dodge Dakota (Still has a little paint left on it)

I think the constant flow of fuel through the rail keeps it cool, too.
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I'm JohnMc, and I approved this message.

understood...so IF this were the setup I would need some sort of Bleed Valve Just in case. Better make sure my injector seals are fresh!

I would like to place the FPR at the rear near the tank/pump.

This is the way the fuel system on a C70 is set up.

So there would only be one fuel line that runs the length of the car - the regulated pressure line that connects to the rail? And the return (bypass) line would be a very short run, looping from the regulator back into the tank?? Interesting. I don't see why it wouldn't work. In effect, all you are doing is moving the regulator to a new location and shortening the return line to suit.

(Of course the tank vent line to the charcoal can would still be there.)
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Chris - 1990 740, 1973 1800ES (Non-running), 1993 Dodge Dakota (Still has a little paint left on it)