Returnless Fuel System

**dave w** · 12-18-2013

Originally Posted by ezobens

I've been working on designing an EFI fuel system for my 69' Corvette that will be converted to TPI in the near future.
Most of the solutions require a supply and return line with a regulator under the hood.
Being cheap and lazy

, I would prefer to run the least amount of plumbing required for this install.
Looks like the LS motors in the C5 and up Corvettes have a 'returnless' system that only requires one fuel line to the motor.
The earlier C5s used a fuel filter / regulator assembly that maintains 55 PSI- Not sure if this is too high or can be accommodated via tuning?
The later C5s, C6 on up use a combination pump and regulator in the tank. I haven't been able to determine the pressure those run at but if the physical packaging could fit my stock C3 tank, that would be the cleanest solution. By the way, I'll be running the 12200411 PCM.

Has anyone attempted something like this and if so, how did you do it?
Any issues using this approach?
Thanks!
Elm

Last summer I helped with building two SBC Marine MPFI conversions. The return line is just below the fuel pump.

dave w

**delcowizzid** · 12-18-2013

returnless is easy just fit your bypass fuel reg in a tee after the pump and return to the tank at the rear. saves running a line from the engine bay back.there are the odd issue with cars in hotter climates taking a bit to start on hot start after a short heat soak.as the fuel vapourises in the fuel rails much like carbs fed by mechanical pumps back in the day

**Accrdwgnguy** · 12-19-2013

feed and return in, feed to fuel rail out. Uses GM quick disconnect fittings, you can get these fittings off junkyard GM cars or use the AN adapters.

The higher pressure to going to up your fuel injectors flow rate, fuel injector rates are typically advertised at 43.5 psi.

**ezobens** · 12-19-2013

Originally Posted by Accrdwgnguy

feed and return in, feed to fuel rail out. Uses GM quick disconnect fittings, you can get these fittings off junkyard GM cars or use the AN adapters.

The higher pressure to going to up your fuel injectors flow rate, fuel injector rates are typically advertised at 43.5 psi.

Understood-
I will need to base my injector sizing based on the PSI I intend to run.
Right now I'm deciding if I want to use this filter / regulator arrangement or run with a Camaro style pump with the regulator built in.
Thanks!
Elm

**lionelhutz** · 12-19-2013

Why use that regulating fuel filter when you could just use a regulator set to 43psi so the pressure and flow rate data is good as is?

Apparently, the Camaro (I'm assuming you mean LS1 4th Gen) canister has the wrong fuel sender resistance for the 69 Corvette fuel gauge. I think it's 40-240 ohms and you need 0-90 ohms.

**ezobens** · 12-19-2013

Originally Posted by lionelhutz

Why use that regulating fuel filter when you could just use a regulator set to 43psi so the pressure and flow rate data is good as is?

Apparently, the Camaro (I'm assuming you mean LS1 4th Gen) canister has the wrong fuel sender resistance for the 69 Corvette fuel gauge. I think it's 40-240 ohms and you need 0-90 ohms.

Changing the pressure and flow rate data isn't a huge issue- It's basically the standard LS data.
I'm actually looking at the 5th Gen Camaro pump but it looks like I may need to run a PWM to control the pressure.
Not that I wouldn't mind it, it's just a PWM controller adds another $300 to the price tag...

A 4th Gen pump will also work with some extra plumbing at the tank to utilize the built-in pressure regulator.
Regardless of pump, I don't need the fuel sender because my original C3 sender is still in place and functional. I have no reason to replace that.
Thanks!
Elm