Recirculation circuit for -6 with carbs.. Options

[mb911]

I know @MarkHenry has talked about this but I want to also do this and have a few questions..

I need to buy my stainless lines for my car and my question is that I have a PMO regulator that has a return to the tank and am using Webers on my -6.. Should I be running all 4 lines from Tangerine or is there another better option?? I want this system safe..

[Mark Henry]

Couple questions:
1) I think Mark mentioned this on other threads, but with a bypass regulator and return line, you should be able to run the stock FI pump on a /4, correct? What are the pros and cons of running a higher pressure pump with a bypass? One advantage for me is one less thing to buy but wondering about performance, reliability, and longevity.

A pump is just a pump, it doesn't build pressure, that's the regulators job. Put a FI pump on with no regulator and it won't build any pressure, lots of flow, but no psi. Main difference between the two pumps is the FI pump has a built in one way valve and working with the reg can generate the higher pressure.
If you think about it a stock /4 FI reg may be set to higher psi but it's still bypassing 99% of the time.

In researching bypass regulators, another question has popped up. Is the 8mm return line large enough to handle the return flow from a stock EFI pump while maintaining a low 3-4 psi to the carbs? Aeromotive suggests a 3/8" (9.5mm) return line for most stock EFI pumps to prevent restricting return flow to the point it builds pressure above the regulator setpoint. Sounds like the setup I'm contemplating has been used successfully before but thought I'd check.

I wouldn't worry about it unless you have 500+HP and are running a much larger pump.

The return is low pressure as soon as the leaves the regulator. The only high pressure is from the pump outlet to the regulator, so technically stock location two 4" pieces of FI hose, four FI clamps and the plastic (or SS) fuel line is the only thing high pressure in the circuit.
Low pressure to the carbs, all the rest of the system is no pressure just flow.

If you want to do an experiment get a FI pump hook it to 10' of gas hose and T in a pressure gauge. You won't see any pressure on the gauge, not unless you stick something like a MIG welder tip in the end of the hose.
I've only tried this with a low pressure pump (carter) but a .024 Mig welder tip is what was needed to build 3 PSI.