Is there a better way? - fuel pump for supercharged engines
01-22-2003, 10:00 PM
#1
Is there a better way? - fuel pump for supercharged engines
I've been following the supercharger fuel pump threads and I understand that we are using these big electric pumps and regulators because we need the ability to increase fuel pressure with boost levels. But it seems backwards to run these pumps at full capacity all the time only to dump most of the volume back into the tank?" Like everything else mechanical, it must be hard on the pump to run full speed all the time.
Why can't we run the pump at different RPMs to suit the flow rate and pressure required. A differential pressure sensor would sense both boost and fuel pressure and a controller would vary the voltage to the pump motor to maintain the proper differential between them. If the engine is under load and needs more fuel, it would tend to reduce the pressure differential so once again the controller would increase pump RPM.
Now you don't need to pass full volume through the pump at all times, you don't need a regulator or a bypass line back to the tank. You don't need the volume of fuel to cool the pump either, since you aren't working it hard all the time. This approach might not work on fuel injected engines since they need such high fuel pressure to begin with, but it might work on blowthrough carb setups. Any thoughts?
Why can't we run the pump at different RPMs to suit the flow rate and pressure required. A differential pressure sensor would sense both boost and fuel pressure and a controller would vary the voltage to the pump motor to maintain the proper differential between them. If the engine is under load and needs more fuel, it would tend to reduce the pressure differential so once again the controller would increase pump RPM.
Now you don't need to pass full volume through the pump at all times, you don't need a regulator or a bypass line back to the tank. You don't need the volume of fuel to cool the pump either, since you aren't working it hard all the time. This approach might not work on fuel injected engines since they need such high fuel pressure to begin with, but it might work on blowthrough carb setups. Any thoughts?
01-23-2003, 05:48 AM
#2
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Technically is possible.... If I'm not wrong, many ignition boxes are capable of driving alternate fuel lines (for those nitrous oxide guys), much probably you can run a double or triple fuel line with smaller electrical pumps and drive some by-pass valvles.
Think on this image:
- Mechanical fuel pump feeding fuel for low rpm conditions.
- When throttle is yanked, ignition box surely can drive alternate electrical fuel pumps to provide additional fuel pressure to the engine.
Major trade-off:
- Need to run a computer capable of driving multiple fuel lines.
- Major burden on your bilge with the additional fuel pumps and tubing with by-pass valvles.
Better to stick to a high volume fuel pump and let that unused fuel return to the tank.
Think on this image:
- Mechanical fuel pump feeding fuel for low rpm conditions.
- When throttle is yanked, ignition box surely can drive alternate electrical fuel pumps to provide additional fuel pressure to the engine.
Major trade-off:
- Need to run a computer capable of driving multiple fuel lines.
- Major burden on your bilge with the additional fuel pumps and tubing with by-pass valvles.
Better to stick to a high volume fuel pump and let that unused fuel return to the tank.
01-23-2003, 06:39 AM
#3
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OK, Tomcat,
The reasons for running the electric pumps at full volume all the time are many. The electric motor is under much less stress when it is less loaded like it would be to dead head the pressuer. Next, the fuel circualtion cools the pump and anything the fuel runs through. It takes less current to run when recirculating, too. These pumps are designed to run like this. Some of the older designs could dead head and not overheat or anything, pumps like Holley, Mallory, etc. bypass in their housings like an oil pump.
There are several ways to run the electric pump as backup only, the simplest I know of is a pressure switch in the fuel line-when the pressure drops below the switch level, the electric comes on. There are many other ways that are less expensive than a computer or control box. The OEM guys would do anything to save money or get better economy, and they run their pumps continuously with a bypass.
How many horsepower are you making? Is it draw through or blow through? Draw through, you can make a lot of power on a good mechaincal pump alone, like the six valve pumps from several manufacturers
The reasons for running the electric pumps at full volume all the time are many. The electric motor is under much less stress when it is less loaded like it would be to dead head the pressuer. Next, the fuel circualtion cools the pump and anything the fuel runs through. It takes less current to run when recirculating, too. These pumps are designed to run like this. Some of the older designs could dead head and not overheat or anything, pumps like Holley, Mallory, etc. bypass in their housings like an oil pump.
There are several ways to run the electric pump as backup only, the simplest I know of is a pressure switch in the fuel line-when the pressure drops below the switch level, the electric comes on. There are many other ways that are less expensive than a computer or control box. The OEM guys would do anything to save money or get better economy, and they run their pumps continuously with a bypass.
How many horsepower are you making? Is it draw through or blow through? Draw through, you can make a lot of power on a good mechaincal pump alone, like the six valve pumps from several manufacturers
Last edited by blown1500; 01-23-2003 at 06:59 AM.
01-23-2003, 07:19 AM
#4
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Aeromotive makes a fuel pump controller and even one for a returnless fuel system too: http://www.aeromotiveinc.com/product...at=Accessories I have not seen them in any marine application though.
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01-23-2003, 08:14 AM
#6
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I looked at this a long time ago and farted around with it a little. Things I noticed are;
1) It was suprising how the inertia of the fuel in the line played a role, when trying to control the pressure with pump speed.
2) The ordinary pressure transducers used with fuel pressure gauges are very slow and have too narrow of an actuation window.
These two things conspired to cause one heck of a delay in the control loop. I'm sure they could be overcome with enough attention, but were beyond the backyard mechanic. That would be a neat scenario. If you don't run the pump anymore than you have to, it doesn't need to be cooled. One could also easily derive an indication of when the control loop was against the rail, indicating either too much pressure, or not enough.
1) It was suprising how the inertia of the fuel in the line played a role, when trying to control the pressure with pump speed.
2) The ordinary pressure transducers used with fuel pressure gauges are very slow and have too narrow of an actuation window.
These two things conspired to cause one heck of a delay in the control loop. I'm sure they could be overcome with enough attention, but were beyond the backyard mechanic. That would be a neat scenario. If you don't run the pump anymore than you have to, it doesn't need to be cooled. One could also easily derive an indication of when the control loop was against the rail, indicating either too much pressure, or not enough.
01-23-2003, 08:40 AM
#7
Good answers all.
blown 1500 - I agree that the pump is not working very hard at low pressures and the fuel can keep lines cool. I'm talking about blowthrough.
Andrea and Raypanic - Looks like Aeromotive has already got the computer to do this for returnless fuel systems. They use an adjustable rate of rise knob instead of monitoring pressure differential.
Brad Perry - There are pressure transducers that respond instantly, and they might work with Aeromotive's computer. This might overcome the lag problem.
You would have to weigh the cost of the computer and sensor against the benefit of not having to plumb the return line and regulator. I might try this...some day.
blown 1500 - I agree that the pump is not working very hard at low pressures and the fuel can keep lines cool. I'm talking about blowthrough.
Andrea and Raypanic - Looks like Aeromotive has already got the computer to do this for returnless fuel systems. They use an adjustable rate of rise knob instead of monitoring pressure differential.
Brad Perry - There are pressure transducers that respond instantly, and they might work with Aeromotive's computer. This might overcome the lag problem.
You would have to weigh the cost of the computer and sensor against the benefit of not having to plumb the return line and regulator. I might try this...some day.
01-23-2003, 09:07 AM
#9
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I also am trying to understand the fuel pump issue. On my 900sc, I have both mechanical and electric systems on both motors. A toggle switch can override the electric pump and the motors run great on just the mech.pump or with both operating. The electric unit plumbs into the mechanical pump. I assume that the electric unit is for safety so if the demand is too great for the mech. pump a lean condition, hence burnt pistons doesn't happen. When I tested the boat before I purchased, the owner ran it on mechanical only but I'm certain Mercury put them there for a reason. Any ideas guys? Thanks Doug
01-23-2003, 10:48 AM
#10
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Hello, Guys,
tomcat, you can boost reference most mechanical pumps. pm and I'll explain. Also, Aeromotive makes a boost referenced pressure regulator with a bypass. So do Mallory and some others. They have worked great for me in relatively low boost situations, like most boats. The return line entry point is important. I like to make a small surge tank. pm for details. Also, the 500EFI uses the water separator/filter as the surge tank and they seem to work fine. A blow thru system for carbs works just like FI only at a lower pressure. Most centrifugal blower manufactureres have such systems. I have one on the engine I was supposed to dyno today. They have always been bulletproof for me before.
NordicHeat, the MSD device you mentioned is generally ment to be used on near stock applications and is used to increase fuel pressure and volume on an otherwise incapable fuel pump. More voltage to an electric motor causes it to work harder giving more potential fuel flow and pressure capabilities. A proper sized pump should not need the extra boost.
27daytona, I have been using two pumps on some blower applications for years. I use a pressure switch, sometimes two in different locations, to turn on the electric pump. I originally did this to "save" the electric pump as they were not as reliable as modern ones. Different applications require different methods. I can tell you how to do this, draw thru or blow thru and be quite effective and safe. pm for specifics
tomcat, you can boost reference most mechanical pumps. pm and I'll explain. Also, Aeromotive makes a boost referenced pressure regulator with a bypass. So do Mallory and some others. They have worked great for me in relatively low boost situations, like most boats. The return line entry point is important. I like to make a small surge tank. pm for details. Also, the 500EFI uses the water separator/filter as the surge tank and they seem to work fine. A blow thru system for carbs works just like FI only at a lower pressure. Most centrifugal blower manufactureres have such systems. I have one on the engine I was supposed to dyno today. They have always been bulletproof for me before.
NordicHeat, the MSD device you mentioned is generally ment to be used on near stock applications and is used to increase fuel pressure and volume on an otherwise incapable fuel pump. More voltage to an electric motor causes it to work harder giving more potential fuel flow and pressure capabilities. A proper sized pump should not need the extra boost.
27daytona, I have been using two pumps on some blower applications for years. I use a pressure switch, sometimes two in different locations, to turn on the electric pump. I originally did this to "save" the electric pump as they were not as reliable as modern ones. Different applications require different methods. I can tell you how to do this, draw thru or blow thru and be quite effective and safe. pm for specifics
Last edited by blown1500; 01-23-2003 at 10:54 AM.
