Fuel line as a "reservoir"

[MCODECUDA]

Your going through a lot of trouble trying to fix a problem that you don’t even know exists. Run it on a quarter mile track first. What’s your engine, transmission and rear end ratio?

 

[RemCharger]

Your going through a lot of trouble trying to fix a problem that you don’t even exists. Run it on a quarter mile track first. What’s your engine, transmission and rear end ratio?

He's got 1-2 psi at 660' .

 

[33 IMP]

For what its worth.....
I did the "welded sump to a stock tank, big fuel line to a badboy mechanical pump" bit,, on my 62. 440 bracket/street car.
When I changed to a Paxton 150gph electric, and an 8 gallon fuel cell, I picked up a half second.

 

[RJRENTON]

Had 1/2 or little more in gas in the tank, I think it cover the pickup.

I was thinking of the red one just because I could activated with a switch when I rolling in to the water. I have a Holley Black pump on the self so I am all ears her.

Battery is in the trunk.

Im looking in my old gas tank and thinking of welding a sump an a 8-an in that one, and let the sender just reading the gas level.

Out of curiosity, how much volume will be gained by increasing the line size from 5/16" OD to 3/8" OD or from 3/8" OD to, say 1/2" OD? The cross sectional area of the tubing X the overall length of the tubing run determines the volume. It sounds like your best solution is the one presented by #19, which energizes the tank (or near by) mouhted fuel pump, for as long as the switch is closed. This arrangement will overcome the pressure loss of the tubing providing that the pump's volume is sufficient at the specified pressure. Basically force feeding the engine mounted mechanical positive displacement pump.

The Difference Between a Pipe and a Tube​

In the manufacturing industry one often hear terms such as steel pipes or steel tubing. Often times, it is often not clear what the difference is between a pipe and a tube.

Many people think that the word has the exact same meaning and use the word "pipe" and "tube" interchangeably. That's however wrong.
There are a couple of key differences between tubes and pipes

A pipe is a vessel - a tube is structural

• A pipe is measured in terms of its ID (inside diameter)
• A tube is measured in terms of its OD (outside diameter).

A hollow cylinder has 3 important dimensions. These dimensions are:

• The Outside Diameter (OD)
• The Inside Diameter (ID), and
• The wall thickness (wt)

These three dimensions are related by a very simple equation:

OD = ID + 2*wt

One can completely specify a piece of pipe or tube by supplying any two of these numbers.
Just talking out loud.....
BOB RENTON

 

[Ceedawg]

Had 1/2 or little more in gas in the tank, I think it cover the pickup.

I was thinking of the red one just because I could activated with a switch when I rolling in to the water. I have a Holley Black pump on the self so I am all ears her.

Battery is in the trunk.

Im looking in my old gas tank and thinking of welding a sump an a 8-an in that one, and let the sender just reading the gas level.

Ok battery is in trunk. Get a starter relay and mount it next to battery, then one wire from positive to the spade hookup. Run another from big nut terminal to pump. Run a smaller wire up to the switch on carb or dash (whatever way you desire) the reason is you don’t have to use a large amp wire from dash switch to pump, just a short distance in the trunk. Make sure the starter relay is for a manual shift car or you’ll have to run a ground from the neutral safety switch connection.
BTW I used the 3/8” aluminum line in my Duster, about 400 HP with no problems getting the fuel to carb (no mechanical pump)

 

[MCODECUDA]

You could put an adjustable low pressure switch in the fuel line that’s wired into a solenoid that energizes the electric fuel pump. When the fuel pressure drops to a certain point the electric fuel pump starts up.

 

[mala]

For what its worth.....
I did the "welded sump to a stock tank, big fuel line to a badboy mechanical pump" bit,, on my 62. 440 bracket/street car.
When I changed to a Paxton 150gph electric, and an 8 gallon fuel cell, I picked up a half second.

I think the mech pump is capable of feeding a lot of HP if it just have a little help with pushing the fuel to it so it can work properly.

 

[Dragon Slayer]

A mechanical pump is a CONSTANT displacement diaphragm pump. Each stroke can only pump the volume displaced when the diaphragm stretches, creates an inlet suction and pulls in fuel to the chamber. Having a larger inlet does nothing to the volume pumped if the pump can pull in the fuel as a liquid with a smaller pipe.

How much fuel is pumped on the stroke is controlled by the carburetor float system. If the carb doesn't need the fuel and the seat is closed or nearly closed the pressure build up in the inlet line to the carb exerts a force against the diaphragm trying to push fuel. The spring pressure on the pump is the opposing force. When equal the diaphragm stops moving and hangs until the pressure in the fuel line to carb drops. No movement or reduced movement means less volume stroked to the carb, but the carb does not need it. Float is closed.

As far as outlet pressure. Run too little pressure and you run the risk of vaporization of fuel from the heat. Now your pumping gas and liquid which is less mass than pure liquid.
When the diaphragm is full pulled up you have the maximum force from the compressed spring exerted against the diaphragm area. When released to come down this is when fuel pressure is the highest pumping the fuel against a restriction. As the restriction goes away and the diaphragm moves down pushing fuel out the spring lengthens and exerts less force on diaphragm and hence a lower pressure in fuel line. Pressure is more an indicator of fuel velocity. How fast the diaphragm is being accelerated from the spring force.

This is not an electric centrifugal pump where you regulate to a constant pressure.

If your mechanical pump is not capable of providing the fuel, it is too small, or excessive check valve leaks which lower the volume stroked out. Go to the larger 6 valve race pump. It is larger with larger diaphragm which makes for a larger volume of fuel stroked.

I was told the 64-65 Hemi Superstock cars had 5/16" model year fuel line from tank to mechanical pump. Than 3/8" up to carbs. Fueling 2 carbs.

So I agree with the "how do you know your out of fuel" pressure is not a good indicator for a constant displacement pump. You would expect the floats to be open and fuel moving during 1/4 mile run. You would expect them to be closed at idle with a higher pressure in the pits.

 

[mala]

Thanks for your informative answer.

The pump has no problem to feed the engine on the street, and when I nail it with street tires the fuel pressure drop from 7-8 psi to 5 psi. I don't feel comfortable at track with only 1-2 psi in fuel pressure in the high end

As I say before the inlet size on the pump is original AN-10 and out AN-8, that was the reson I was thinking of replacing my 3/8" line from tank to pump to a 1/2" so there is no restriction there.

 

[Dragon Slayer]

That looks like a custom pump, so talk to the manufacturer. Hard to believe it can't keep up. With those big lines I would expect pressure to be lower when the float needle is open and the restriction is less. Doesn't mean your not pumping the necessary volume.

 

[INTMD8]

What size are the internal check valves? Would almost think it would need 4 instead of 2 to flow as much as the fittings on the pump.

 

[RemCharger]

I think the mech pump is capable of feeding a lot of HP if it just have a little help with pushing the fuel to it so it can work properly.

That's like saying a mustang is fast, if there's a Charger pushing it from behind.

 

[68 Sport Satellite]

My friend John owns an A-body. He's got a great fuel supply feeding his stroked motor.
Stock tank, mechanical pump up front. Underhood fuel surge tank with internal small electric pump in the surge tank submersed in fuel. The mechanical pump feeds the surge tank and the surge tank feeds his EFI. No special tank baffling in his stock tank. The surge tank with electric pump is the key. It works amazing and supports close to 600 hp.

 

[Dragon Slayer]

He needs that because it is EFI and that requires higher pressure. The surge tank and pump create the high pressure for the Fuel injection. So not an apple to apple comparison for a carbureted motor.

 

[68 Sport Satellite]

Yes, but it's doable for a carb application also. Radium offers a new surge tank with internal fuel pressure regulator. I'm installing one on my car. You can also use a lower pressure electric pump for carb applications. I used to run an electric 6-8 psi pump with my carb.

FST-R, Fuel Surge Tank with Integrated FPR

He needs that because it is EFI and that requires higher pressure. The surge tank and pump create the high pressure for the Fuel injection. So not an apple to apple comparison for a carbureted motor

 

[Fran Blacker]

Seems like a big dollar fix. I'd eliminate the mechanical pump and run a good electric pump. Having an on/off switch on gas sounds OK but just one more thing to go wrong. Keep it simple. Doesn't say if it's BB or SB or I missed it but if a BB push rod worn down?

 

[mala]

Good point!
But I have measure the push rod. and its good enough (3.220.)

 

[mala]

What size are the internal check valves? Would almost think it would need 4 instead of 2 to flow as much as the fittings on the pump.

Im not sure what you mean with " internal check valves"? Can you develop more.

 

[Dragon Slayer]

This is a carter, not sure who's make yours. Carter rebuildable types have 2 check valves for pulling in fuel and one discharge check valve. Isolating the chambers. Just a rubber disc under the umbrella hat with a light spring.

Also, notice the chamber difference here. The upper has a smaller chamber and is the typical carter 6903 or 4862. Depending on diaphragm spring they can be a higher pressure. The spring force on a smaller piston area equals greater pressure produced but less volume. Vice versa for a larger piston area.

The bottom is the hemi chamber. Notice the gear teeth cut out. It provides a greater volume per stroke. I cc'd them a long time ago and if I remember right, it had a 15% increase in volume. Other subtle difference in the diaphragm assembly also.

The typical non rebuildable carter pumps only have 2 valves. One each. The race are 6 valve. 3 and 3. 2nd picture provided.

A lot of folks run a small electric at tank to feed the mechanical with no issues. Good for priming a car when it has sat and fuel evaporated too.

You can skin a cat a lot of ways and you can over engineer also. There are calculators on web that will give you your fuel requirement per minute for the hp of your engine. I think you would find mechanical pumps can do fine for most street type cars unless your really radical on the HP.

 

[mala]

This is inside the pump, old pictures that I found in cell phone. So I don't have any measurement on the inside ports.