I am putting a 66 Mustang fuel tank in my 65 Dart. Tank is from Spectre, has a 255 ltr rating, is in tank.
My plan is to run a log type return regulator (made by Moroso) very close to the tank, set at 15 psi. Close to the carb i will have a holley regulater set at 7 psi. I plan to run 3/8 line from tank to pump, bypass back to tank, and up to the holley regulator. The 3/8 line is feeding my 408 just fine , but the electric pump is noisy. If there is a flaw in my plan, please discribe.

You're putting lots of work into the fuel, I would look at what options are out there to PWM [pulse width modulate] the fuel pump for the lower demand.

I don't think you need two regulators. You can use a high pressure regulator up by the carb that drops the pressure from 60 psi to 6 psi. You will need a full length return line. The nice thing about a setup like that is if you buy the correct regulator you won't need to touch the system if you ever switch over to EFI. Just screw in the adjuster and you'll have 43 psi at the injector rails.

what regulator would you recommend andy ?

There are low pressure for carbs & high pressure ones for EFI. I have the QF return for a carb on my set up, DO NOT get one with a bypass jet inside, that is for mechanical pumps with a return.

Holley 12-880 should work but there are other choices depending on what size of line you are using and if you want o-ring or pipe fittings.

https://www.holley.com/products/fue...s/regulators/efi_regulators/parts/12-880

Thats cool, I see it has 2 different springs,

Here is the one I have it is less expensive
https://www.summitracing.com/parts/qft-30-900qft/overview/

Thanks Andy. I currently have all the parts i talked about, but that 12-880 would be the clear deal if my parts don't work together well.

I ran a similar setup to what you described in your original post except I was using an external Walbro GSL392. I didn't want to have to run a large return line the entire length of the car and I was concerned that the pressure drop in a 3/8 return line could exceed 5-6 psi when returning nearly 100% of pump output at idle.

I made my own bypass setup using a relief valve that I adjusted through trial and error to get about 12-14psi in the return loop when full flow of the pump was bypassed. Up front I suppose any regulator would do but I used an Aeromotive 13205 because I got a deal on a nearly new one.

This wasn't really a high performance application and in hindsight a Walbro GSL391 would have been a better choice at 190LPH vs. 255 for the GSL392

doesn't seem to work ?

thanks andy. question #2. if a guy uses a regulator on a log ram with EFI throttle bodies, do you use two regulators ?

No, you shouldn't need two regulators on a long ram engine. Long ram engines won't make enough power to require two regulators but a person might need two regulators on a tunnel ram full race engine. I've used a single regulator up to 900 hp so that is well past what most stock block Mopar engines are going to need.

thanks again andy

For a return line IIRC the 440 6 pack steel fuel filter had a small 3rd nipple for a return line.