[jhein]

Originally Posted by JLMounce

A -6 feed and return is likely okay, especially if you were moving to EFI where fuel pressures are greater. For a carbureted application, it may be better to run a -8 feed and return.

Jay S has mentioned on a couple occasions the heating effect of forcing fuel through the smaller lines becomes more of an issue with a carburetor.

So the fuel overheats and causes vapor lock in carb application?

[JLMounce]

Originally Posted by jhein

So the fuel overheats and causes vapor lock in carb application?

If you think about how this works in an EFI vs a carbureted platform, it makes a bit of sense.

There's far less pressure in the fuel lines when running this system carbureted, so there's more fuel flow (flow increases and pressure decreases) which would cause some friction heating as the fuel flows through the lines.

Because the carburetor also has fuel bowls that act as a reservoir, you're passing much more fluid through the whole system at all times. The larger line slows down the column of fuel, which in theory should create less fuel heating.

I don't know if that's really going to be a huge concern or not though. You can always run an inline heat sink too if it ever becomes a problem.

[67Lemons]

Originally Posted by JLMounce

If you think about how this works in an EFI vs a carbureted platform, it makes a bit of sense.

There's far less pressure in the fuel lines when running this system carbureted, so there's more fuel flow (flow increases and pressure decreases) which would cause some friction heating as the fuel flows through the lines.

Because the carburetor also has fuel bowls that act as a reservoir, you're passing much more fluid through the whole system at all times. The larger line slows down the column of fuel, which in theory should create less fuel heating.

I don't know if that's really going to be a huge concern or not though. You can always run an inline heat sink too if it ever becomes a problem.

It almost sounds as if it would be better to run a short loop by mounting the regulator near the tank so no warm fuel enters back into the system?

[jhein]

Originally Posted by JLMounce

If you think about how this works in an EFI vs a carbureted platform, it makes a bit of sense.

There's far less pressure in the fuel lines when running this system carbureted, so there's more fuel flow (flow increases and pressure decreases) which would cause some friction heating as the fuel flows through the lines.

Because the carburetor also has fuel bowls that act as a reservoir, you're passing much more fluid through the whole system at all times. The larger line slows down the column of fuel, which in theory should create less fuel heating.

I don't know if that's really going to be a huge concern or not though. You can always run an inline heat sink too if it ever becomes a problem.

OK, but for the carb application, isn't the pressure only lower on the carb side of the regulator? Why would the pressure be lower in the feed line in a carb application?

I'm not saying that I won't do the -8 lines, I just want to understand why and make sure it's necessary before I start returning parts and piecing a new system together.

[Jay S]

I have tanks systems feeding a carb, there are a few different issues that you run into feeding carbs versus FI systems. When feeding a low pressure carb the pump flow rate is about 30% higher at 7 psi than feeding 40 psi on a EFI system. All that extra fuel gets returned constantly unless your at full throttle, with the extra fuel flow the fuel is extra warm when pushed thru a 3/8” line. I have noticed fuel even gets warm thru 1/2” line on my cars with the tanks system. With the small line and oxygenated fuel, feeding a carb, fuel pressure is not as consistent, and depending on the fuel and your carb set up vapor locking can be an issue. It isn’t that the 3/8” line won’t work most of the time, it will, but it does not work near as good as 1/2” line when condition that are hot or feed near as much HP.

With a carb set up the best results are to set it up so the fuel line from the pump to go directly to the carb and the regulator plumped in after the carb. Similarly to what I am saying with 3/8” line versus 1/2” line, it isn’t that you can’t put the regulator before the carb and plumb into the return, but it works best set up differently, less prone to vapor locking and more constant supply.

If you were determined to run 3/8” line, you might look into using a smaller 190 pump instead of a 255.