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..

[bbrock]

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.

2) What is the advantage of D over C? C looks to be the stock setup with allowance for a relocated pump. Just curious.

[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.

2) What is the advantage of D over C? C looks to be the stock setup with allowance for a relocated pump. Just curious.

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.

I would imagine that D over C would be good due to potential pressure drop after passing through the first carb

No difference, in theory C would be slightly better because it's always cool fuel right at the carb.
By that logic in a FI system each injector down the line would have less pressure, which is not the case.
In layman's terms think of it like a parallel vs series electrical circuit, parallel doesn't lose voltage. The fuel circuit flow is much like a parallel circuit, therefore no pressure drop.
Note that in C the fuel just bypasses through the carb inlet port, it doesn't go into the float bowl and back out.

[bbrock]

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.