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FAQ - EFI Fuel Pumps

1.) I’m looking at an Aeromotive EFI fuel pump for my new engine but I need 60 PSI and your catalog (or your website) says it only puts out 43 PSI, do you have one with more pressure?

It’s a common misconception for people to think that a particular fuel pump “puts out” a specific pressure.  Though some pumps are pressure limited, which we’ll explain in a moment, the fact is no pump “puts out” any pressure.  What a pump does do is put out flow.  And what it needs to do is put out the necessary flow when regulated up to the required pressure for a particular application.

All electric pumps have a flow curve that changes with pressure.  Not all companies advertise or provide these flow curves, which can make evaluating a fuel pump for a particular application virtually impossible.  At Aeromotive we understand that a pump’s flow curve across a range of pressure reveals crucial performance characteristics about any pump, so when we quote flow, we always provide the test pressure and voltage.  When you read how much an A1000 flows at 43 PSI, you’re being given vital information that is in the proper context; how much flow at what pressure.  This doesn’t mean the pump “puts out” 43 PSI.

There are basically two types of pumps used in automotive fuel systems, those that are pressure limited, for use with a static (non bypass) regulator, and those that are not pressure limited, and which must be used with a dynamic (bypass style) regulator.  Pressure limited pumps are almost all intended for use with carbureted engines, and the static style carburetor regulators designed for 3-12 PSI.  What happens with a pump like this is that when the flow is blocked by the regulator to prevent high pressure from flooding the carburetor, a bypass at the pump opens to prevent pressure from going too high at the pump.

Some pressure limited pumps have an internal bypass (usually the lower flow, street/strip type) that opens around 15 PSI and allows the flow from the outlet port to travel through an internal passage in the pump, back to the inlet port.  The higher flow, racing specific pumps often feature an external bypass, set for 18-24 PSI.  Here a return line is run from the fuel pump back to the top of the fuel tank so that when the maximum pressure is reached the excess flow returns to the tank.  Either way, these pumps are not intended for use in high pressure, EFI systems, even if the bypass is blocked to force pressure higher.

Many Aeromotive pumps are of the “non pressure limited” type, including the A1000 for example.  This type of pump cannot be used with a static (non bypass) regulator, because to stop the flow coming from the pump completely would drive fuel pressure to 100-PSI or higher, creating excessive current draw and heat, and potentially damaging the pump permanently.  Non pressure limited pumps can be operated in both low (carbureted) and high (EFI) pressure systems, as long as the proper bypass regulator is used.

Aeromotive, adjustable bypass regulators are available to use with non pressure limited pumps that can handle flow from small to large pumps, and that can create and maintain pressure from carbureted to EFI levels.  Most EFI regulators are adjustable from as low as 30 PSI to as high as 70 PSI, so those who want 43 PSI for the fuel rail will be able to use the same pump and regulator combination as those who want 60 PSI.  Just be sure the pump provides the necessary flow at the pressure you need.

 

2.) I’m building a new EFI combination, what fuel pump do I need?

Choosing the right fuel pump can seem complicated and confusing, but it doesn’t have to be.  Aeromotive is an engineering company that approaches fuel delivery in a sophisticated, but surprisingly practical way.  At Aeromotive we take a “pump-centric” approach to fuel delivery.  This means we assess the fuel flow needs of our customers, including how much volume and at what pressure.  Once we’ve established what is needed, the starting point is to engineer a fuel pump that can meet that flow and pressure requirement.

New pump development is itself an exhausting process that includes prototyping and testing, then more prototyping and testing, but once we know we can deliver a pump that will meet the objective and may be moved to durability and field testing, we begin a parallel effort to develop the supporting components required to create a complete fuel system around that pump.  Everything from pre and post filters to port sizes and port fittings are considered.  We also engineer and develop a specific regulator that will maximize efficiency of that pump, enabling the buyer to extract every possible ounce of available flow while maintaining the desired pressure.  The result is a complete fuel system with specific capabilities.

What does this mean to you?  It takes the guess work out of choosing the right fuel delivery, and THAT makes your life easier in a meaningful way.  All you have to do is determine what pump will meet your requirements.  From there the system is defined and either available under one part number or outlined with respect to the individual components you need in our easy to use “Aeromotive Power Planner”.  The “Power Planner” is available in our catalog and on our website at www.aeromotiveinc.com, at the top of any page, just click on the “Power Planner” link and choose the EFI Power Planner with one more click.

The “Power Planner” outlines fuel systems one at a time, starting with the lowest horsepower combinations and, as you scroll down, covering applications capable of increasing levels of horsepower.  The two main questions you need to answer are simply “what will the engine’s peak horsepower be?”, and “What will the fuel system require for fuel pressure?”, including base pressure and boost reference if that is required.  If you’re not sure of what your engine will make power-wise, there are numerous magazines and internet forums where you can research similar combinations to the one you’re building, that have already been dyno tested, to get you solidly in the ballpark.

It’s a good idea to be somewhat optimistic when estimating horsepower, or if you prefer, build in a little head room, just to make sure you cover the bases completely.  Keep in mind, all ratings provided by Aeromotive are based on flywheel horsepower.  Horsepower at the tire must be corrected up to flywheel horsepower.  It’s safe to allow 15% drive line losses, so you can divide advertised wheel horsepower numbers by 0.85 to get the flywheel estimate.  For example, 500 WHP divided by 0.85 equals 588 FWHP.

Every Aeromotive fuel pump is rated for its horsepower capability on the specific product page found in our catalog, and on our website.  You will see several horsepower ratings that apply to various engine combinations, naturally aspirated to forced induction, as well as for carbureted and fuel injected engines, where a given pump is capable of supporting flow and pressure for both.

For more detailed information on how to accurately calculate fuel delivery to support horsepower, see Aeromotive Tech Bulletin TB-501 at www.aeromotiveinc.com under the Tech Help, Tech Bulletin section.

 

3.) After 30 minutes or so of driving, fuel pressure starts to fall, then the fuel pump gets louder and/or seems to quit running altogether.  What’s wrong, is my pump going bad?

You may be experiencing EFI vapor lock.  Even though the fuel is recycling through the car, eliminating localized hot spots, the recycled fuel is still being exposed to under-hood engine heat.  Fuel in an EFI bypass system does slowly warm up as it is recycled through the chassis, the fuel rail(s), engine compartment, and finally back to the tank.  The longer an EFI engine runs, the higher fuel tank temperatures can become. Unlike the more common carburetor vapor lock, where fuel is heated to boiling in the float bowl(s) or fuel line(s) under the hood, EFI vapor lock is often caused by hot fuel in the tank.

Excessive pump noise along with fluctuating or dropping fuel pressure often indicate that fuel temperature is high enough to cause hot fuel handling problems.  A combination of high fuel temperature and low pressure can result in cavitation, where liquid fuel changes to vapor.  In a return style EFI fuel system, the most likely place for these conditions to exist in the same place, at the same time, is at fuel pump inlet.  Once cavitation starts, it will feed upon itself.  As vapor enters the pump, it displaces liquid fuel required to lubricate the mechanism, allowing metal to touch metal, creating even more friction and heat.  Once the pump begins to super heat, a complete vapor lock will develop. 

In order to prevent cavitation and vapor lock, correct fuel system design and installation are vital.  Ensure supply lines and inlet filters meet hi-flow, low restriction requirements and are kept clean.  Keep the tank full on hot days.  Reduce fuel pump speed and recycle rate with a fuel pump speed controller during low load, idle and cruise conditions.  Carefully route fuel lines and plan component placement to avoid exhaust heat. Do not overlook proper tank ventilation, if the vent line or vent valve do not allow ample air to move freely in both directions, fuel delivery problems will never fully resolve.  Any conditions that restrict the pump’s access to fuel in the tank must be addressed. 

 For more detailed information on installation issues that can result in premature cavitation, hot fuel handling problems and vapor lock, see Aeromotive Tech Bulletins TB-101, TB-102 and TB-802, all of which can be found at www.aeromotiveinc.com under the Tech Help, Tech Bulletin section.

 

4.) My fuel pump has been getting louder and louder, now it seems to turn on and off, or it blows the fuel pump fuse, why?

The first thing to check in this situation is the post fuel filter.  Ensure it is the proper Aeromotive filter and that the element is not clogged.  The post filter should be replaced at the minimum once per year in the spring, just before the driving season begins.  It’s also possible your fuel pump is experiencing significant cavitation caused by conditions described in earlier FAQ’s., or it have been damage from debris.  If normal steps to ensure a good installation do not resolve the issue, contact the Aeromotive Tech Support staff for assistance in diagnosing the problem and obtaining service if necessary.  In the event your pump should need service or repair, an RGA is required, so be sure to call first before shipping.

For more detailed information on the importance of a clean, free flowing outlet filter, see Aeromotive Tech Bulletin TB-102 at www.aeromotiveinc.com under the Tech Help, Tech Bulletin section.

 

5.) Why are Aeromotive fuel pumps rated for more horsepower on a naturally aspirated engine than they are for a forced induction engine?

Two factors effect an electric fuel pump’s rated ability to support horsepower, one is the max pressure  the fuel pump has to produce and two is the HP consumed by any engine accessories ahead of the flywheel.  Higher fuel pressures created by “boost reference” fuel systems, common to forced induction EFI engines, force electric pumps to slow down against the increasing load, reducing available fuel pump volume.  A forced induction engine also requires more fuel to support HP developed in the cylinder but lost to the work required to drive the compressor helping to make the extra power.

For example, supercharged engines consume HP to drive the turbine via a belt.  Turbo chargers trap exhaust heat and flow to drive the compressor, creating what are termed “pumping losses” caused by exhaust back pressure working against the piston on the exhaust stroke.

Any electric fuel pump must be de-rated for forced induction because it will support less flywheel HP.  It’s interesting to note that things aren’t always what they seem; if you add back the HP lost to the compressor, the pump actually supports the same cylinder HP for forced induction as it does naturally aspirated, just less of what is developed in the cylinder remains to be measured at the flywheel.

For more information on how to accurately compensate for forced induction fuel consumption, see Aeromotive Tech Bulletin TB-501 at www.aeromotiveinc.com under the Tech Help, Tech Bulletin section.

 

6.)  I need a fuel system that can run high base fuel pressure between 70-120 PSI continuous.  What Aeromotive electric fuel pump and regulator can I use?

This is a question that arises from time to time, and the first answer is; no single, Aeromotive electric fuel pump is currently suitable for continuous duty above 70 PSI.  Notice I said no “single” fuel pump is suitable, we’ll expand more on that in a moment.  There are several Aeromotive EFI Bypass Regulators that will support adjusting base fuel pressure in this range, including P/N 13113 for between 50-90 PSI base, as will  P/N’s 13132, 13133 and 13134, with the 75-130 PSI spring installed.

The real question is what fuel pump can reliably support this high range of operating pressure while maintaining substantial fuel flow.  With the exception of P/N 13134, all the regulators noted above are engineered for use with Aeromotive mechanical (belt or hex drive) fuel pumps.  When operating pressures this high are required for a special application, a mechanical fuel pump is by far the best choice.

The downfall of driving a pump with an electric motor is that as pressure goes up the work load increases and the motor slows down.  As the motor slows down the pump slows with it, resulting in less and less flow as pressure goes higher and higher.  While it’s possible to build an electric motor that, with low voltage (12-16 volts is nothing in the world of electricity) is able to maintain high RPM at high pressure, the size and weight, not to mention excessive current draw of a motor like this, make the idea impractical at best.

A mechanical pump is driven by the engine itself, remaining small, lightweight and drawing zero current.  There is a small load placed on the engine to run the pump at high pressure, but at 2-3 horsepower it’s hardly substantial compared to the engines available power.  Of course, no way is the engine going to be slowed down by the pump as pressure increases, so the mechanically driven fuel pump is able to maintain high RPM at high pressure, making it extraordinarily good at producing and maintaining high flow.

Okay, mechanical pumps are best, but is it possible to use electric pumps at highly elevated pressures?  Yes, but, only if we’re talking about pumps (plural).  This is a special application requiring two pumps of similar flow capacity to be plumbed into the system in a specific way.  This approach is referred to as plumbing “in series”.  Of the two ways we can plumb multiple pumps into a single system, using pumps “in series” means one pump feeds another, with the first pump drawing from the tank and feeding the inlet of the second pump.  The other approach to plumb multiple pumps is called “in parallel”, where each pump has its own draw from the tank and the outlets are joined together to a single line that then feeds the engine.

The benefit of plumbing pumps “in series” is different than plumbing them “in parallel”.  Plumbing pumps “in parallel” produces a system that can deliver the combined flow of both pumps at any pressure, but don’t forget at very high pressure that may not mean much… At terminal pressure, zero times two is still zero.  Parallel plumbing can be very valuable in a system requiring substantial flow but at normal pressure.

Plumbing two pumps “in series” produces a system that can deliver the same flow as one pump but at their combined pressure.  In other words, two identical pumps “in series” can flow the volume of one pump but at twice the pressure.  Plumbing pumps “in series” is a means of preserving flow at high pressure, working to offset the normal flow reduction due to high pressure slowing the motor.  This has limited value in systems operating at normal pressures, but can prove very valuable in extreme, high pressure situations.

The technical aspect of this involves knowing how to select two pumps which, together, will accomplish the objective of supplying the necessary flow at the required pressure.  We start with how much flow will be required to support the engine, and at what pressure.  We then need to consult the flow curves for various pumps that may be combined “in series”, selecting pumps that would be compatible.  Finally we have to know how to predict what the chosen pumps can flow at the pressure desired.  The following method can predict the approximate flow available from two pumps, “in series”, at a specific pressure:

To find the flow volume available from two pumps plumbed “in series”, at a desired pressure, find the point on each pump’s flow curve where their volume is equal.  Note the pressure at which this occurs for each pump.  Add the two pressures together, the sum represents the pressure where that flow volume, common to both pumps, is available when they are combined and “in series”.

Combining two pumps of equal size “in series” is desirable, and makes it easy to project performance.  For example, take two A1000 fuel pumps “in series”, you know they have the same flow curve (flow the same at any pressure).  All we have to do is just divide the desired pressure in half and then check the A1000 flow curve.  For example, if we needed 120 PSI, divide by two for 60 PSI.  The A1000 flow curve shows 700 lb/hr at 60 PSI.  For a forced induction engine take a BSFC of 0.65, divide the 700 lb/hr flow by 0.65 to see 1,077 flywheel horsepower (FWHP) is possible.  It would be safe to expect one A1000 to support 1,000 FWHP at 60 PSI and two A1000’s plumbed “in series” to support 1,000 FWHP at 120 PSI.

WARNING: Combining pumps “in series” that have substantially different flow curves is not a good idea and will probably create more problems than it solves.  For example, trying feed an A1000 with a stock fuel pump in the tank would starve and damage the A1000.  A good rule of thumb to avoid problems would be to combine pumps with a differential flow of no more than 10-20%.  

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