Is there any improvement on adding a return gas line on this truck
Like adding Gas line return for from the Carb and manual fuel pump to the Gas tank increase gas mileage?
Has anyone done this?? Or is it a myth?
I changed things on my 1979 F150 for the 4.6 that I run in it I just thought something close to that would help the 351m.

 

That sounds like a bunch of hokum to me. First of all, on a carbed engine, what would be the purpose of a return line, and how the heck would you plumb it into the carb? I guess I could see a return line on the back end of a fuel log, so long as the appropriate pressure is going to the carb, but as far as I've seen, most carbs are feed and forget, not feed and return.

Now, if you're going to convert your 351 to EFI, then a return line is required as the electric fuel pump will feed the fuel rail for the injectors at the specified pressure set by the regulator, but anything past that gets circulated back to the tank. That would also presuppose that you're installing an EFI manifold, fuel regulator, rail, injectors, MAF meter, EFI computer, return line, adapt the old gas tank for EFI (as it's a pressurized system), electric in-line fuel pump, mechanical fuel pump block off plate, in-line high pressure fuel filter (like those metal ones in later EFI trucks), and I'm sure a few things I've forgotten.

Also, if your 351 is a 335 class engine instead of a windsor, you'd have to find an EFI manifold to fit, which i'm sure there's something out there, but they're not abundant.

By the way, if you already put a 4.6 into one of these trucks, you already know all this stuff. Basically, I think it's a myth, as the engine is going to use the amount of fuel it needs...period. Now, an EFI engine is most likely going to get better mileage, but that's due to the better atomization of fuel, not whether or not it has a return line. Better atomization means hotter burn, means less fuel needed for the same power, means better mileage. So, if you convert your 351 to EFI, then yes, I'd say you'd get better mileage, but you need to find the correct parts to do it first, and there's not a ton out there for the 351m.

 

Hey thanks for the info I was thinking Myth But I heard people talking about it but not seen it done.

 

I put one on my 74 - but its EFI.