Planning ahead for FI

[mdprovee]

While I am putting my car back together, I am trying to make as much of the changes for FI as posible now. I plan on running two carbs on a tunnel ram for about a year, then swith over to FI. So I have some questions.

Now I have a 1/2" fuel line running from rear to the front of the car..what size return line should I put in the car?

When I order my new fuel tank, I want to get the pump inside the tank, again capable for FI. I believe the fuel pressure is a lot higher for FI than a carb. Do I just use a regulator at the motor and then run the excess fuel down the return line? Is there another way to do this?

Does someone make a regulator with one inlet, two outlets, and a return outlet?

Thanks for any help.

Mike

[Rick@Rick's Hot Rod Shop]

Mike,

Aeromotive makes a regulator that has One inlet, Three outlets, and One Return. This Regulator is adjustible from 3 to 20 PSI with the low pressure spring installed, and 20 to 60 PSI with the high pressure spring installed. The nice thing about this regulator is that you can use it for the low pressure of the carbuetor and when you convert to EFI it should be able to handle that too.
As for the return line. On our tanks with the in-tank Bosch, Delco, or Walbro pumps we have found that -6 is enough but we have gone as far a putting a -8 on the tanks with the in-tank A1000.

[Fuelie Fan]

Sounds like you've got the concept. There's some details in the execution.
Depending on if you go TBI or MPI, you may have to alter which fuel pump you select. TBI usually operates at 11-15 psi, and MPI is usually 43.5 psi. Sometimes, you can just buy a pump designed for MPI and regulate it down to TBI pressure levels, especially if you think you may upgrade later. But, it depends on the pump and the regulator. When we used a GM TBI on a dyno that had a gargantuan pump (I think he said it flowed enough for 1500 hp), the outlet of the gm regulator could not handle the flow rate and therefore the pressure was stuck up around 30 psi. An aftermarket regulator will work around this, but i've used a few of them and, though they can handle super high flow rates, it's usually in a pretty ugly fashion, as the pressure isn't very stable when compared to an OE design.
As a side note, with a 255 l/hr pump, the gm regulator works fine. And, in TBI, it's hidden up inside the throttle body, which means less firewall clutter.
I'll second Rick's comments on the return. 3/8 return should be fine for most applications. Our testing has shown that, at least on OE style regulators, that the pressure setpoint is relatively insensitive to return line restrictions. In fact, we had to produce 9-10 psi of downstream restriction before the supply pressure (set as 11 psi)started to increase.

[mdprovee]

Thanks guys for your help, this will give me a little more info to work with.

Rick,
I need to purchase a tank anyway.. could I order one from you, with a fuel pump inside for the carbs. Then when I want to switch to FI, could I pull out the old pump and put a new one for FI in, and hook up the return line. Would that be an option for me?

Mike

[Rick@Rick's Hot Rod Shop]

Mike,


Yes we can set you up with a tank with the provision for the intank pump. You can go one of two ways when running carbs. We can install a low psi pump for this. Or you can go with an external pump and use the return side of the F.I. provision for a pick-up with the send side plugged. When youre ready for F.I. all you have to do is select a pump for your application and install it and youre ready to go!

https://www.pro-touring.com/forum/showthread.php?t=8864
Check this out. This is our dual pump setup. A set up for your application will look similar minus the second provision.

[mdprovee]

Thanks Rick,

I will be giving you a call in a few months.

Mike

[yody]

all of the companies like aeromotive etc. Will ALL tell you to at least run a line the same size or bigger then your supply line for your return. So you would probably want at least an 8AN if not 10

[Blown353]

For a carb'd application, run the same size return line as the feed line. A smaller return line will cause a restriction which will bump up the fuel pressure at the regulator.

On a EFI system running 45+ psi of fuel pressure, this restriction won't be a problem. On a low pressure carb'd system, you may not be able to turn the regulator low enough as the small return line will be a restriction causing more pressure at the regulator. When I had my car carb'd I had -8 feed and -8 return lines and with the regulator dialed all the way out I still had 3 psi of pressure due to backpressure in the return line.

Troy

[mdprovee]

Thanks guys that will help me.

Mike