It has been my experience that, yeah, you need a bypass type regulator so as to ensure a constant/minimum flow of fuel through the electric fuel pump as that flow is what cools the pump's motor.
And, you need to size the return line just as large as the supply line as a minimum. One size larger would be ideal.
- My OEM fuel pickup module is somewhat modified.
- I've a Walbro 392 pushing from the frame-rail next to the tank's pickup, into the OEM fuel filter in the head, into an Aeromotive boost referenced bypass type regulator, and finally into the IP.
- All the fuel supply plumbing is 6AN (3/8" ID).
At one time, I had the regulator's bypass return line simply Tee'd into the stock/OEM return line (5/16" OD).
- It supplied fuel just fine at the time. The problem was; At WOT, if I side-stepped the throttle, fuel would spit from the regulator's case O-ring (a result of the spike in supply pressure when I quickly got off it).
To fix that, . .. now . . .
- I've a 6AN return from the fuel pressure regulator's bypass.
- I've a 4AN return from the IP.
- I've a 4AN return from the fuel injector's return rail.
- The above three returns play into a small aluminum fuel manifold (adjacent to the battery).
- The above manifold has an 8AN return headed back toward the fuel tank.
- Just ahead of the driver's rear tire, in the fender space, there's a fan assisted fuel cooler. (IIRC, it's actually 10AN bushed down to 8AN).
- The above plays back into the modified fuel pickup module (8AN).
No more fuel spitting from the regulator.