Fuel System

[jwebb]

Running a stroked 351 with a carb, do I need a return line to tank, and if so, how? Lost please help!

[Gordon Levy]

Depends on what pump you use but as a general rule, no.

[Railroad]

It might be easier to run one now, in the event you change over to EFI. Some regulators, even for carbs, utilize a return line.

[JRL16]

Mine only has 1 line from the tank to the mechanical fuel pump. Agreed it would be easier to put in the return line now even if unused for possible future EFI. Future EFI would also need electrical work.

[brewha]

With your 351, you should upgrade the size of the feed line also.

[NAZ]

Like Gordon said, depends on what pump you use. But before determining what pump to use you need to know how much fuel you need to supply the carb. Specifically, the rate of fuel burn so you can determine the supply rate at the required pressure. From there you can size the fuel line(s) and pump as well as determining if you need a regulator and a return line. For a garden variety SBF with moderate power and used on the street you're probably better off using a simple engine driven OEM style diaphragm pump. But again, you need to know the burn rate to select the correct size mechanical pump and verify your fuel line is sized correctly.

[BB767]

A couple of you have mentioned up sizing the fuel line. How much? I am getting a 351W based 427, @500 HP. What size fuel line should I, and the gentleman above, use? I assume the line provided in the Roadster kit is insufficient. It will have a Holly 750 with mechanical pump initially but may upgrade to EFI in the future so I do plan on installing a return line (unused for the time being).

[JRL16]

Sounds like we have the same engine and carb BB767. Got mine from engine factory and they told me to use 3/8 line. I bought the fuel tank single feed line from Breeze and it's a 3/8 tube also.

[NAZ]

Let’s assume your naturally aspirated street engine burns .5lbs of fuel per hour per horsepower at WOT. 500HP x .5lbs = 250lbs/hr burn rate. Convert that to GPH by dividing 250 lbs by 6.2 lbs (weight of a gallon of gas) and you get ~40 GPH average burn rate at WOT to produce 500 HP. However, you’ll want some margin there so let’s add 25%, which will get you to 50 GPM. So you need a pump AND fuel supply system that will supply your carb 50GPM of fuel at 6 to 8 PSI if running a carb. Remember, if you are looking for an electric pump make sure you review the pump curve at the voltage you have to the pump.

Now what size fuel line do you need? You have to account for pressure drop when sizing your plumbing needs. Let’s look at two popular size fuel lines that might be used on these cars; specifically -6AN (3/8”) and -8AN (1/2”). We’ll compare pressure drop of 14’ of fuel line and 50 GPH flow rate. The -8 will drop ~0.5 PSI in that length and the -6 will drop twice that. So if the pump will put out 50 GPH at 8 PSI your 3/8” fuel line will probably be OK as long as the fuel filter doesn’t add much to the total pressure drop. If the pump will put out more than 8 PSI when deadheaded you will need a regulator if running a carb. Now you'll have to choose from a regulator that uses a return line or one that doesn't.

[BB767]

OK, thanks. Food for thought.

[CraigS]

This is really easy to run fuel line.Very flexible and never rusts.
https://shop.advanceautoparts.com/p/nicopp-nicopp-nickel-copper-brake-fuel-transmission-line-tubing-coil-3-8-x-25-cnc-625/22190270-P?searchTerm=3%2F8+nicopp