Underhood fuel line routing help

[Tommy]

Regarding your plans for the fuel pressure regulator - I recommend a regulator with one input and two outputs (one to the carb and the other back to the fuel tank). They are much easier on the fuel pump. If you do that, you may want the regulator just after the pump so you don't have to run the return line so far.

[767Jockey]

Originally Posted by Tommy

Regarding your plans for the fuel pressure regulator - I recommend a regulator with one input and two outputs (one to the carb and the other back to the fuel tank). They are much easier on the fuel pump. If you do that, you may want the regulator just after the pump so you don't have to run the return line so far.

Actually the Mallory 250 GPH pump has a built in return, so I only need to run the return line from the pump back to the tank, and use a deadhead regulator.

[Cobrabill]

Originally Posted by 767Jockey

Actually the Mallory 250 GPH pump has a built in return, so I only need to run the return line from the pump back to the tank, and use a deadhead regulator.

That system passes up a great opportunity to cool the fuel,which in any equation is a great thing.

[767Jockey]

Originally Posted by Cobrabill

That system passes up a great opportunity to cool the fuel,which in any equation is a great thing.

How does a longer return line equate to cooler fuel?

[Tommy]

Sorry about my bogus advice above. I just looked at the Mallory 250GPH pump and your plan looks OK to me. The important thing is that there be a way for excess fuel from the pump to go back to the fuel tank. Some pumps simply reroute the excess fuel back to the intake side of the pump, allowing fuel to recirculate next to the heat of the pump for an extended time. Those types of pumps can lead to to vapor lock.

[Ron61]

Originally Posted by 767Jockey

How does a longer return line equate to cooler fuel?

Just the same as water going through the radiator. The longer it is going through the cooler it will be. A longer return line will have the fuel in it a little longer than a short one which will let some of the heat transfer to the line and the air will cool the line some if it is where air can get to it. That is why I didn't run my fuel lines inside the frame.

Ron

[767Jockey]

In theory I understand this. In actuality, I would be shocked to see any measurable difference in fuel temp, and even if you could measure it, the change in HP is probably zero, especially with that "cooler" fuel being dumped into a tank that holds over 40 gallons of ambient temp fuel..

[Cobrabill]

Originally Posted by 767Jockey

In theory I understand this. In actuality, I would be shocked to see any measurable difference in fuel temp, and even if you could measure it, the change in HP is probably zero, especially with that "cooler" fuel being dumped into a tank that holds over 40 gallons of ambient temp fuel..

6-7...Just so i know we're on the same page:

1)Fuel line leaves the tank and enters the pump which is mounted near the tank.
2)Return line leaves the pump and goes to the tank or the pump by itself-no return line?
3) line runs to the fuel rail and dead ends at the rear of it.

[JeepSnake]

Doug,

Actually, the long return line acting like a radiator has little to do with the way the return style system works to keep the fuel cool. The circulation is what's important.

Think about a regular old carbureted fuel system: no regulators, no return. Just a fuel pump, a line, and a carb. Unless the engine is really loaded and consuming a lot of fuel, there is a bunch of fuel sitting static in the fuel line. As it sits there, the fuel line absorbs heat from the engine & headers and transfers it to the fuel. This can wind up resulting in vapor lock.

So, to solve this problem, you add a return line near the carb, and you put in a higher volume fuel pump. Now, the pump is always moving fuel through the fuel line, even when the engine isn't loaded, and returning it to the fuel tank. This cures the heating/vapor lock issue in two ways: 1) the moving fuel doesn't have as much time to pick up heat as it passes through the engine compartment fuel lines, and 2) what heat it does pick up is dispersed into the heat sink of 20+ gallons of fuel in the tank. As a friend put it to me, you keep the fuel moving and it doesn't have time to just hang out and get in trouble.

In the '70s, as engine operating temps increased, this system was incorporated into production cars to fight vapor lock. I know that Jeeps used a fuel filter just ahead of the carb with two outlets. One fed the carb, the other returned fuel to the tank so that you didn't vapor lock while creeping offroad.

Hope this helps.