External Fuel Pump Question
05-18-2004, 10:43 AM
#1
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Location: Indy, IN. USA
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External Fuel Pump Question
Is anyone using an external fuel pump only, while still using full exhaust in the stock location? If so how did you route your lines from the tank to the pump?
The reason I'm asking is I have fuel delivery problems using the Aeromotive System for our cars. Yeah I know I'm going to get the "Aeromotive is junk" line. But please spare me unless you have actually used an Aeromotive pump, and can back up the claims.
The Aermotive system utilizes a 3/8 rubber line that goes in place of the stock pump. Basically the A1000 pulls fuel out the top of the tank to the pump and the pump pushes it forward.
The problem is after about 30 minutes the FP starts to jump around and will not go up with minimal throttle input. I think the pump is cavitating. To solve this I was going to sump the stock tank but then realized everyone I see that has sumped the tank usually has exhaust that dumps before the rear axle.
The reason I'm asking is I have fuel delivery problems using the Aeromotive System for our cars. Yeah I know I'm going to get the "Aeromotive is junk" line. But please spare me unless you have actually used an Aeromotive pump, and can back up the claims.
The Aermotive system utilizes a 3/8 rubber line that goes in place of the stock pump. Basically the A1000 pulls fuel out the top of the tank to the pump and the pump pushes it forward.
The problem is after about 30 minutes the FP starts to jump around and will not go up with minimal throttle input. I think the pump is cavitating. To solve this I was going to sump the stock tank but then realized everyone I see that has sumped the tank usually has exhaust that dumps before the rear axle.
05-25-2004, 05:38 AM
#2
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Join Date: May 2003
Posts: 2,275
I'm using an A1000 with the near stock exhaust and original tank that I sumped. I ran the 8an supply and 6an return in almost the same place as the original fuel lines. After I tore out the factory lines. I think you should look at a couple of things before you fire up your fuel pump again.
First understand the difference between cavitation and aeration. Your problem with feeding off the top of the tank can result in aeration. Cavitation is the result of the inlet side of the pump being restricted and the high amount of suction actually pulls the air out of the liquid. Aeration will pull air for example from leaky gaskets or seals. In your case the movement of fuel in the tank and high rate of suction is causing a vortex. Kind of like the problem of using a high volumn oil pump with a standard size sump.
Second, why is your pump "moving"? I bolted mine to the floor pan near the drivers seat. Granted it isn't all that quiet but it won't move.
First understand the difference between cavitation and aeration. Your problem with feeding off the top of the tank can result in aeration. Cavitation is the result of the inlet side of the pump being restricted and the high amount of suction actually pulls the air out of the liquid. Aeration will pull air for example from leaky gaskets or seals. In your case the movement of fuel in the tank and high rate of suction is causing a vortex. Kind of like the problem of using a high volumn oil pump with a standard size sump.
Second, why is your pump "moving"? I bolted mine to the floor pan near the drivers seat. Granted it isn't all that quiet but it won't move.
05-25-2004, 06:33 AM
#3
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Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
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Pulling up and over the top of the tank can lead to problems. You're "lifting" the fuel, and reducing the "net positive suction head" below the level required for the pump. When the fuel in the tank starts to heat up from the high recirculation rates, and passing near hot engine and exhaust components on the way, it increases the vapor pressure of the fuel, and you can get fuel vapor bubbles in the suction line to the pump. Additionally, "pulling" the fuel forward in the suction line places the pump under excessive peak strain when you pull high G's on launch, and all the fuel in the system is pushing backwards, reducing the pump discharge pressure at exactly the moment you want max flow.
I run dual pumps, one in the stock in-tank location, and one off a sump at the back of the tank. This way, on acceleration, the fuel is being pushed into the suction side of the pump, reducing the potential for vaporization of pressure reduction. The "sump" is completely internal with a stilling well and a screen. The only thing you can see at the back of the tank is a -10AN fitting welded in:
http://cjcfo.fbody.com/members/injun.../DCP03576a.jpg
Fits fine, with or without an exhaust.
I run dual pumps, one in the stock in-tank location, and one off a sump at the back of the tank. This way, on acceleration, the fuel is being pushed into the suction side of the pump, reducing the potential for vaporization of pressure reduction. The "sump" is completely internal with a stilling well and a screen. The only thing you can see at the back of the tank is a -10AN fitting welded in:
http://cjcfo.fbody.com/members/injun.../DCP03576a.jpg
Fits fine, with or without an exhaust.
Last edited by Injuneer; 05-25-2004 at 06:35 AM.
05-25-2004, 08:25 AM
#4
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Location: Indy, IN. USA
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Originally posted by slopokrodrigez
I'm using an A1000 with the near stock exhaust and original tank that I sumped. I ran the 8an supply and 6an return in almost the same place as the original fuel lines. After I tore out the factory lines. I think you should look at a couple of things before you fire up your fuel pump again.
First understand the difference between cavitation and aeration. Your problem with feeding off the top of the tank can result in aeration. Cavitation is the result of the inlet side of the pump being restricted and the high amount of suction actually pulls the air out of the liquid. Aeration will pull air for example from leaky gaskets or seals. In your case the movement of fuel in the tank and high rate of suction is causing a vortex. Kind of like the problem of using a high volumn oil pump with a standard size sump.
Second, why is your pump "moving"? I bolted mine to the floor pan near the drivers seat. Granted it isn't all that quiet but it won't move.
I'm using an A1000 with the near stock exhaust and original tank that I sumped. I ran the 8an supply and 6an return in almost the same place as the original fuel lines. After I tore out the factory lines. I think you should look at a couple of things before you fire up your fuel pump again.
First understand the difference between cavitation and aeration. Your problem with feeding off the top of the tank can result in aeration. Cavitation is the result of the inlet side of the pump being restricted and the high amount of suction actually pulls the air out of the liquid. Aeration will pull air for example from leaky gaskets or seals. In your case the movement of fuel in the tank and high rate of suction is causing a vortex. Kind of like the problem of using a high volumn oil pump with a standard size sump.
Second, why is your pump "moving"? I bolted mine to the floor pan near the drivers seat. Granted it isn't all that quiet but it won't move.
Thanks for shedding some light on the difference between cavitation and aeration. So do you think it is cavitation? According to your description of the two, it would seem that because my pump is sucking so hard to get fuel out of the top of the tank it is pulling the air out of the liquid.
Why is my pump "moving"? Well I guess I may have used the FP in the wrong way. I meant FP to mean Fuel Pressure, not Fuel Pump. My pump is solid as a rock, in the same place as yours!
I would really like to see your set-up. With the tank and exhaust installed we can see no way to get the fittings and line far enough away from the exhaust for it not to heat up.
Here is the solution we came up with. I bought a new tank, and some 5/8 steel tubing. We are going to drill a hole in the front portion of the tank above the diff, toward the drivers side. Then bend the tubing along the bottom of the tank to the very back and use it for the pick-up point. Then we will connect it to a -8 bulkhead fitting and run -8 hose to the pump inlet. I essence it will work just like a sump becasue even with a sump the pump must still pull the fuel around the tank and up to it. One good thing about our solution is that the fuel is in the tank longer and hopefully that will help it keep a little cooler. I hope that makes since.
05-25-2004, 08:34 AM
#5
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Join Date: Jan 2002
Location: Indy, IN. USA
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Originally posted by Injuneer
Pulling up and over the top of the tank can lead to problems. You're "lifting" the fuel, and reducing the "net positive suction head" below the level required for the pump. When the fuel in the tank starts to heat up from the high recirculation rates, and passing near hot engine and exhaust components on the way, it increases the vapor pressure of the fuel, and you can get fuel vapor bubbles in the suction line to the pump. Additionally, "pulling" the fuel forward in the suction line places the pump under excessive peak strain when you pull high G's on launch, and all the fuel in the system is pushing backwards, reducing the pump discharge pressure at exactly the moment you want max flow.
I run dual pumps, one in the stock in-tank location, and one off a sump at the back of the tank. This way, on acceleration, the fuel is being pushed into the suction side of the pump, reducing the potential for vaporization of pressure reduction. The "sump" is completely internal with a stilling well and a screen. The only thing you can see at the back of the tank is a -10AN fitting welded in:
http://cjcfo.fbody.com/members/injun.../DCP03576a.jpg
Fits fine, with or without an exhaust.
Pulling up and over the top of the tank can lead to problems. You're "lifting" the fuel, and reducing the "net positive suction head" below the level required for the pump. When the fuel in the tank starts to heat up from the high recirculation rates, and passing near hot engine and exhaust components on the way, it increases the vapor pressure of the fuel, and you can get fuel vapor bubbles in the suction line to the pump. Additionally, "pulling" the fuel forward in the suction line places the pump under excessive peak strain when you pull high G's on launch, and all the fuel in the system is pushing backwards, reducing the pump discharge pressure at exactly the moment you want max flow.
I run dual pumps, one in the stock in-tank location, and one off a sump at the back of the tank. This way, on acceleration, the fuel is being pushed into the suction side of the pump, reducing the potential for vaporization of pressure reduction. The "sump" is completely internal with a stilling well and a screen. The only thing you can see at the back of the tank is a -10AN fitting welded in:
http://cjcfo.fbody.com/members/injun.../DCP03576a.jpg
Fits fine, with or without an exhaust.
In my reply above to "slopoke", I tried, as best I could, to describe the solution we came up with. I know it is probably not as good as a sump, but I am confident it will work when we are done. And it is definately much better than what I have.
What do you think?
05-25-2004, 10:47 AM
#6
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Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,677
If possible, you want the pump suction connection at the back of the tank.... that's where the fuel heads under acceleration. The force of the fuel moving backward will help "force feed" the pump under acceleration. Do it the other way, and the accelation pulls the fuel back out of the pump suction, increasing the possibility of vaporization. Make the pump suction connection as large as you possibly can... -10AN is better than -8AN.
My intank pump works the same as the stock pump... submerged, pushing the fuel forward through a billet filter. The "outboard" pump only runs when the nitrous system is armed. It pulls out of the sump in the rear of the tank, and pushes into an NOS "Y" fitting just before the filter.
Some interesting pump "tech", not specific to fuel pumps, but helpful:
My intank pump works the same as the stock pump... submerged, pushing the fuel forward through a billet filter. The "outboard" pump only runs when the nitrous system is armed. It pulls out of the sump in the rear of the tank, and pushes into an NOS "Y" fitting just before the filter.
Some interesting pump "tech", not specific to fuel pumps, but helpful:
SUBJECT : Cavitation
Cavitation means that cavities are forming in the liquid that we are pumping. When these cavities form at the suction of the pump several things happen all at once.
-We experience a loss in capacity.
-We can no longer build the same head (pressure)
-The efficiency drops.
-The cavities or bubbles will collapse when they pass into the higher regions of pressure causing noise, vibration, and damage to many of the components.
The cavities form for five basic reasons and it is common practice to lump all of them into the general classification of cavitation. This is an error because we will learn that to correct each of these conditions we must understand why they occur and how to fix them. Here they are in no particular order :
-Vaporization
-Air ingestion
-Internal recirculation
-Flow turbulence
-The Vane Passing Syndrome
Vaporization .
A fluid vaporizes when its pressure gets too low, or its temperature too high. All centrifugal pumps have a required head (pressure) at the suction side of the pump to prevent this vaporization. This head requirement is supplied to us by the pump manufacturer and is calculated with the assumption that fresh water at 68 degrees Fahrenheit (20 degrees Centigrade) is the fluid being pumped.
Since there are losses in the piping leading from the source to the suction of the pump we must determine the head after these losses are calculated. Another way to say this is that a Net Positive Suction Head is Required (N.P.S.H.R.) to prevent the fluid from vaporizing.
We take the Net Positive Suction Head Available (N.P.S.H.A.) subtract the Vapor Pressure of the product we are pumping, and this number must be equal to or greater than the Net Positive Suction Head Required.
To cure vaporization problems you must either increase the suction head, lower the fluid temperature, or decrease the N.P.S.H. Required. We shall look at each possibility:
Increase the suction head
-Raise the liquid level in the tank
-Raise the tank
-Mount the pump lower
-Reduce the piping losses.
These losses occur for a variety of reasons that include :
-The system was designed incorrectly. There are too many fittings and/or the piping is too small in diameter.
-Solids have built up on the inside of the pipe.
-A suction strainer is clogged.
-Be sure the tank vent is open and not obstructed.
-Something is stuck in the pipe
-The inside of the pipe, or a fitting has corroded.
-A bigger pump has been installed and the existing system has too much loss for the increased capacity.
-Lower the fluid temperature
-Insulate the piping
-Be careful of discharge recirculation lines, they can heat up the suction fluid.
-Reduce the N.P.S.H. Required
Cavitation means that cavities are forming in the liquid that we are pumping. When these cavities form at the suction of the pump several things happen all at once.
-We experience a loss in capacity.
-We can no longer build the same head (pressure)
-The efficiency drops.
-The cavities or bubbles will collapse when they pass into the higher regions of pressure causing noise, vibration, and damage to many of the components.
The cavities form for five basic reasons and it is common practice to lump all of them into the general classification of cavitation. This is an error because we will learn that to correct each of these conditions we must understand why they occur and how to fix them. Here they are in no particular order :
-Vaporization
-Air ingestion
-Internal recirculation
-Flow turbulence
-The Vane Passing Syndrome
Vaporization .
A fluid vaporizes when its pressure gets too low, or its temperature too high. All centrifugal pumps have a required head (pressure) at the suction side of the pump to prevent this vaporization. This head requirement is supplied to us by the pump manufacturer and is calculated with the assumption that fresh water at 68 degrees Fahrenheit (20 degrees Centigrade) is the fluid being pumped.
Since there are losses in the piping leading from the source to the suction of the pump we must determine the head after these losses are calculated. Another way to say this is that a Net Positive Suction Head is Required (N.P.S.H.R.) to prevent the fluid from vaporizing.
We take the Net Positive Suction Head Available (N.P.S.H.A.) subtract the Vapor Pressure of the product we are pumping, and this number must be equal to or greater than the Net Positive Suction Head Required.
To cure vaporization problems you must either increase the suction head, lower the fluid temperature, or decrease the N.P.S.H. Required. We shall look at each possibility:
Increase the suction head
-Raise the liquid level in the tank
-Raise the tank
-Mount the pump lower
-Reduce the piping losses.
These losses occur for a variety of reasons that include :
-The system was designed incorrectly. There are too many fittings and/or the piping is too small in diameter.
-Solids have built up on the inside of the pipe.
-A suction strainer is clogged.
-Be sure the tank vent is open and not obstructed.
-Something is stuck in the pipe
-The inside of the pipe, or a fitting has corroded.
-A bigger pump has been installed and the existing system has too much loss for the increased capacity.
-Lower the fluid temperature
-Insulate the piping
-Be careful of discharge recirculation lines, they can heat up the suction fluid.
-Reduce the N.P.S.H. Required
05-25-2004, 11:01 AM
#7
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Thread Starter
Join Date: Jan 2002
Location: Indy, IN. USA
Posts: 153
Thanks for that info. It is helping very much.
I actually made a mistake saying we are using a -8 bulkhead fitting. We are using 5/8 tubing in the tank connected to a -10 bulkhead and braided -10 to the Aeromotive Filter.
We are going to slash cut the end of the tubing in the tank to make picking up the fuel easier. Do you think we should make a nice flowing bend of 180 degrees so that when I take off the fuel in the tank pushes itself into the tubing? It will still have to travel around the bend and forward but your theory make since that you want the fuel sloshing back to help you fill the need of the pump.
Please let me know.....
TIA!!!!
I actually made a mistake saying we are using a -8 bulkhead fitting. We are using 5/8 tubing in the tank connected to a -10 bulkhead and braided -10 to the Aeromotive Filter.
We are going to slash cut the end of the tubing in the tank to make picking up the fuel easier. Do you think we should make a nice flowing bend of 180 degrees so that when I take off the fuel in the tank pushes itself into the tubing? It will still have to travel around the bend and forward but your theory make since that you want the fuel sloshing back to help you fill the need of the pump.
Please let me know.....
TIA!!!!
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