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?

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.

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:eureka:

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.

I would say if Aeromotive makes it it will not tear up their pumps by running at reduced voltage.

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.

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.

Tom, this may work for you. Apparently it increases voltage to the pump with boost.
MSD 2350
http://www.jegs.com/cgi-bin/ncommerc...83&prmenbr=361

Dave

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

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:D :D :D

Tomcat:

Running an electric pump at a constant voltage, and using a bypass after your caburetor (or fuel rail) that is boost referenced. Will be the most efficent way of running your system. Since these pumps run off of DC power they are very voltage sensitive, if you get a little more or less resistance in your wirig it will change your pressure. Running a bypass after feeding your carburetor allows the pump to free flow, running very cool, and drawing less amperage. This is also safer since the fuel will take the path of least resistance going into an empty bowl rather than try to return all the way back to the tank.


Doug
Tech @ Barry Grant, Inc.

doug -

what empty bowl are you talking about? if you run the regulator after the carb, it still dumps excess fuel into a return line that has to go back to the tank, right?
please elaborate.

The technoligy has come a long way as well with these elec. fuel pumps. I run the 1000 ser. Aeromotive, and they are rated at full pressure for 5000hrs. I don't think my engine or even boat for that mater will get 5000 hrs worth of use:p

Since your bypass would be after the carburetor the float bowls will always have fuel rather than getting bypassed, this will also account for spikes in fuel demand that a voltage regulated system would not.

Doug

Tech @ Barry Grant, Inc.

tomcat what you are looking for is a variable speed constant pressure pump. I deal with these at work so I am familiar with them with pumping water. Grundfos make what they call a SQE pump. it is computer controlled and will deliver (lets say for example , it depends on the pump) 60 psi at 2 gpm and or 60 psi at 8 gpm. a sensor in line will feel a slight pressure loss and tell the pump to accelerate to compensate for the increase in volume. this kind of system will eliminate the need for a large water storage tank but it does require something to hold pressure on the system so the pump has a cushion to push against near the sensor to take some shock out of the system and allow some reserve volume for the sensor to take a split second to do it's job. the tank is no bigger than a foot ball. This is a great system and you will feel no lag or loss in pressure as long as your demand don't exceed the pumps capabilities. the on thing I don't like is that the system is delicate and venerable to power serge's. my opinion is if it can be done with water it can be done with fuel. but I don't think it would be a good of system to put up with the abuse of a Hi performance marine environment.

I hope this helps

Paul