Radium's Ultimate Fuel Pump Test


As part of our Fuel Surge Tank (FST) line, Radium Engineering carries various fuel pumps from select manufactures that differ in flow rates. Third party independent flow testing data on these pumps can sometimes be found with research on the web.  However, the data can be inconsistent between sources, presented in a way that makes comparison difficult, or may not exist at all.  This makes it hard to compare pumps directly. To remedy the issue we decided to do our own in-house back to back comparison test of all six fuel pumps we currently offer with our FST product line. This information would equip us and our customers with the knowledge to correctly choose a specific Radium FST.

The test measured pressure, flow rate, voltage, current draw, and sound level. The sound was measured in decibels (dB) using the sound level meter below...

For some customers building street cars, fuel pump noise is an important aspect. This test would give a good comparison between all the pumps.

Shown below are the six fuel pumps that were tested. All units were brand new off the shelf.

Top Row: Bosch 044 (External Pump), Bosch 040 (Internal Pump)
Bottom Row: Walbro 400 E85, Walbro 400 Gas, Walbro 255, Aeromotive 340R

The flow test used a simple controlled orifice. The fuel pump line was restricted by the orifice until the desired line pressure was achieved and then flow was tested using a timed interval. The volume of fluid the pump output during the timed interval was measured to provide the volume per unit time (flow rate) at each line pressure.  As always, Mineral Spirits (specific gravity of .76) was used for the testing fluid. We are aware that there are more accurate (and expensive) ways to flow test fuel pumps, but this setup was adequate for us to compare the fuel pumps in identical test conditions. Also, note that these results should not be compared to other tests, since our test setup is inherently unique. So lets get to the results.

Flow Rate

Note: To convert to PSI, just multiply the Bar pressure by 14.5

The above chart shows the new Walbro 400 and Walbro 400 E85 have superior flow when compared to the others, even the "mighty" Bosch 044. One interesting note is that unlike the other pumps, the two Bosch pumps maintain flow level extremely well as pressure increases.

We generated this table as a rough guide to use when estimating the Horsepower supporting capacity of the fuel pumps. This guide is approximate and there should always be a built-in safety factor when selecting the pump.

Current Draw

Looking at electrical current, one can almost make the assumption that the more current the pump draws, the more it flows. The high flowing Walbro 400 pumps draw close to 20Amps at 6 bar! There are a couple exceptions to this though. For instance, the Aeromotive pump required more current than the Bosch 044, but flowed less than it.

The sound level was measured inside the main 5 gallon fuel container. All pumps were fully submerged in the testing fluid. The sound level (shown below) was the average of two readings taken at low and high pressure. Sound is highly sensitive variable and can be influenced greatly by the surroundings, this required extra effort on our part to maintain precise consistency during each sound measurement.

The Walbro 255 takes the prize as the loudest pump followed by the Bosch 044. It is interesting to note that the highest flowing pump in the group (Walbro 400 E85) was also the quietest.
Keep in mind that many factors effect real world pump noise levels in the vehicle and are not reflected in this test. Also, while the Walbro 255 was the loudest in this test batch of pumps, there are many aftermarket branded fuel pumps not included in this test that are considerably louder and do not flow much more, if at all.

So now lets talk value. A certain fuel pump may flow well, but if it costs 5 times more than one that comes close, what is the point? Below is a chart that shows flow per dollar. Note: We used retail prices for all pumps.

The chart shows that the Walbro 255 gives the most flow per dollar spent. In fact, all the Walbro pumps show to be good value. Due to their high price, the two Bosch fuel pumps are not as good a value.


Walbro 255:

Excellent value and proven reliability in a small package. While the loudest of the batch, it is still an OEM quality pump so it is all relative. These pumps are used extensively all over the world and are "hands-down" the most popular in the aftermarket world.
Single Walbro 255 FST
Dual Walbro 255 FST

Bosch 040:
A low current drawing OEM Audi pump with a Bosch badge that offers consistent flow across a wide pressure range. Note: The low current draw will help keep fuel temperatures down. 
Bosch 040 FST

Bosch 044:
This age-old design used on classic Porsche and Ferrari still holds its ground quite well, but its high price and high noise level keeps it from being the best.
Dual Bosch 044-Horizontal FST
Dual Bosch 044-Vertical FST

Aeromotive 340R:
This compact high-current drawing pump heated up our test fluid quite quickly, but also performed quite well and has a reasonable flow per dollar value.
Single Aeromotive 340R FST
Dual Aeromotive 340R FST

Walbro 400 Gas/E85:

These new pumps from Walbro perform extremely well on all fronts; flow, noise level, and value. They set a new bar for flow from a compact package. Just make sure your wiring can handle 20A of current!
Walbro 400 Gas/E85 FST

We hope this information will assist our customers when considering what pump to use with their surge tank.
Radium Fuel Surge Tanks

Automotive Fluid Connections Explained

Radium Engineering deals with fluid connections for automotive applications. Properly connecting fuel, pressurized air, hot oil, etc. is an area in which we have extensive experience. This guide explains the most popular fluid connections currently used in cars for plumbing fuel, oil, coolant, air, and other needs. It will also explain how to properly utilize connections to ensure a leak-free operation. To properly and safely install our products, understanding connections is of the utmost importance. Most of the following information can be found with research, however, we decided to consolidate it in one place and discuss it's relation to automotive applications. Brake line related fittings such as SAE flare, inverted flare, hard lines, etc will not be covered. All listed information is simply a general guide. Please consult with hose and fitting manufacturers before selecting components for safety critical systems. To begin our discussion...

Beaded Stem
Beaded stem fittings work as a hose-to-fitting connection.  This is simply a pipe with a slight flare in it. These are the most common connection types and are found on almost every car. They are inexpensive, effective, and do not require any special end fitting for the hose.  Hoses slide on and secure with a hose clamp. An example of a fuel pressure regulator with beaded stem connetions is pictured.

When using beaded stems and rubber hose for fuel injection systems, EFI rated fuel hose should be utilized that can handle the higher pressures found in modern EFI systems. Fuel injection hoses also require special hose clamps as shown below.

Beaded Stem Summary
Common Automotive Uses: fuel lines, coolant lines, radiator hoses, PCV/Emissions hoses.
Benefits: inexpensive, easy servicing, very common, no hose fitting required, no special tools
Drawbacks: not for extremely high pressure, not for high temperature, not as robust as other fluid connections, requires clamp, aesthetics

Push-Lok Hose Ends

Push-Lok hose barbs are a means to attach a hose-end to a rubber hose. Several sharp barbs lock into the inside diameter of the hose and create a seal. Below is an example of a push-lok hose end.

Depending on hose type, these fittings can be difficult to assemble and may require lubricant. Once installed, they cannot be pulled apart and can withstand several hundred PSI. The hose must be cut to remove to preserve the fitting. Most hose manufacturers offer a hose type specifially made for Push-Lok fittings.  Push-Lok Hose names may vary (i.e. Aeroquip labels them SOCKETLESS fittings, Russell labels them TWIST-LOK, Summit labels them TWIST-TITE).  When fittings are used with the correct hose, hose clamps are not necessary. When using the fitting with a non-Push-Lok rated hose, it is suggested to use a clamp.  This combination would only be appropriate for low-pressure applications and one must be careful to ensure the Push-Lok fitting does not damage the hose when a clamp is used. The barbs have the potential to slice through the walls of non-Push Lok hose.

Push-Lok Hose Barb Summary
Common Automotive Uses: aftermarket fuel systems, vacuum/boost hoses
Benefits: reusable, high pressure rating, will not leak, low cost, no hose clamp required

Drawbacks: Requires special hose, can be difficult to assemble, hose must be cut for removal

Tapered pipe threads
In the US, pipe threads are commonly called NPT (National Pipe Thread). NPT are a fitting-to-fitting connection used for attaching a fitting to a hole or another fitting. They work in a simple, crude and effective manner. The male NPT fitting has threads that are tapered.  In other words, the fitting has a smaller diameter at the tip and then gets gradually larger in diameter farther up the shank. The hole, or female fitting, also has tapered threads.  The difference is that the female fitting has a larger size at the opening of the hole which gets smaller deeper in the hole. As the two are threaded together, the male fitting wedges into the female and the flanks of threads compress into each other forming a seal. See diagram below. Pipe threads are commonly called out by a fractional size such as 1/4NPT or 3/8NPT. More information on sizing can be found here. Teflon (or equivalent) lubricant in the form of paste or tape is used to lubricate the interface and make sure the fittings can be unscrewed in the future.

When using NPT fittings, attention must be paid to materials being used. One of the worst case scenarios is screwing together an aluminum fitting with a stainless steel pipe thread fitting. This combination threaded together can cause the aluminum to "gall" with the stainlesssteel.  Most often the aluminum threads are destroyed if the connection is unscrewed. To remove, it is absolutely necessary to apply heavy amounts of anti-seize while paying careful attention not to over-torque. In general, NPT threads in all materials deform when tightened.  For this reason, they may not seal as well the second time they are used.  This is especially true for soft non-ferrous materials.
Besides NPT, it is important to note there is another family of tapered pipe threads called British Standard Pipe Tapered (BSPT). They work exactly in the same way and look almost identical when similar sizes are compared; however, the threads are slightly different.  An NPT fitting will not properly seal in a BSPT fitting. Many Japanese engine engines (Nissan, Toyota, etc) use 1/8 BSPT holes for the oil pressure switches. When using this size for an aftermarket turbocharger kit, it is often mistakenly for 1/8-NPT fitting. Mixing the two sizes will create a slow leak over time.

NPT Fittings Summary
Common Automotive Uses: valve cover PCV fittings, threaded fluid holes in engine blocks (oil, water etc)

Benefits: inexpensive, very common, no special tools required, can be improperly clocked

Drawbacks: permanently deforms threads, not a positive guaranteed seal, sensitive to installation, some fittings cannot be reused, do not swivel, requires teflon lubricant

-AN Conical Seal (aka J.I.C.)
-AN (Army/Navy) style fittings are commonly spotted in engine bays in red and blue anodized colors. They are very popular to use for all fluid types from oil to fuel to brake lines. History of this style of fitting can be found online. They are also known as J.I.C. fittings (mostly in the hydraulic industrial world) and use a 37 degree conical seal. JIC and -AN fittings can be interchanged with each other. This style of fitting originated in military applications and over the years have made their way into the automotive aftermarket realm. Authentic MIL-spec -AN fittings are constructed to exacting tolerances and are very expensive. Luckily, many automotive aftermarket companies exist today that manufacture -AN "style" fittings that may not be MIL-spec but still work great for our needs. These would include Russell, Earl's, Aeromotive, Radium, Red Horse Performance, and many more.

Here is an example of some -AN hose and fittings being use on a Nissan SR20DET.

These fittings work by mating a tapered conical surface on the male fitting into a reverse tapered surface in the female ftting, shown below. When the B-nut (female side, blue) is tightened it draws the two gold and gray parts together and a metal-on-metal mechanical seal is formed between the two conical surfaces. THE THREADS DO NOT DO ANY SEALING.

Over-tightening the B-nut can cause leaking. It takes suprisingly litle torque to fully tighten an -AN fitting. Many auto parts retailers sell -AN wrenches that are aluminum so they do not marr the surface of fittings. These wrenches are also very short, helping in tight spaces while preventing over tightening. DO NOT USE ANY TYPE OF TEFLON, LOCTITE, SILICONE SEALANT, ETC ON -AN FITTINGS! They are designed to screw together dry. A small amount of light oil may be used to assist screwing the B-nut down in some applications. The male and female tapered conical surfaces need to be clean and free of scratches or dings, otherwise they may leak. More information can be found here.
The 37degree -AN/JIC flare should not be confused with a different fitting type, 45 degree SAE flare.These two are not compatible with each other and will leak!

Photo courtesy of Car Craft Magazine

Shown above, special tools can be used to form a 37 degree flare in hard tubing which allows a leak free way to transition from hard tubing to hose using all 37degree flare fittings. This is useful for plumbing fuel lines on a car. 

The chart below explains how these fittings are referenced. So when you hear "I need a dash six ninety hose end" you know the person is working with 3/8" ID hose.

These fittings are available in a variety of different colors and materials. For most automotive/engine related plumbing, aluminum is suitable. Visit your local high performance parts retailer to see all the options.
-AN hose ends are installed on a hose by different means. The Push-Lok fitting shown above would be used to convert a rubber push-lok compatible hose to be used with an -AN fitting. However, the traditional -AN hose end is assembled to the hose using a screw down collar.




Another way to attach a hose end to a hose is by crimp. Here is a photo of a -AN hose ends that are crimped by a special machine on to the hose.The hose type in this picture is PTFE teflon with a black sheath covering the stainless steel braid material.

Photo courtesy of Edelbrock

The photo above shows several different hose types from Russell Performance, but all have a -AN hose end installed. Why so many different types of hose? Many factors influence what hose to select for your application. Pressure rating, operating environment, aesthetics, cost, ease of assembly, etc. Contact the manufacturer if you are unsure what hose is best for your application.

The photo below shows a small sample of the different hose types and hose-end fittings available from Aeroquip. 




Photo courtesy of Eaton/Aeroquip. Link to Aeroquip Product Catalog

-AN Conical Seal (J.I.C.) Fittings Summary
Common Automotive Uses: aftermarket plumbing of fuel, air, coolant, and oil, used on racing vehicles of all types

Benefits: positive seal, uninterrupted flow, wide variety of fitting and hose configurations available, easily serviced, suitible for high pressures and temperatures, very robust connection, easy to disassemble, most can swivel after assembly
Drawbacks: high cost, assembling hose-end to hose can be labor intensive

O-Ring Port
O-Ring port fittings (commonly called ORB for short) are an excellent way to attach a -AN hose to a threaded hole. They work by compressing an O-ring into a chamfered groove around the opening of the threaded hole. This creates a reliable seal and is easily serviceable. The female hole MUST have the the chamfer at the opening in order for the O-ring to work properly. If there is no chamfer, the O-ring will be damaged from extreme compression and the fitting will never fully tighten up. The male and female threads are both straight threads, no tapers on this one. The standard is to use -AN threads for these port fittings. This means that the threads are the same as the threads on the 37 degree tapered -AN fittings shown above. This is handy because you can slip an O-ring onto a tapered -AN fitting and thread it into an O-ring port hole and it will work perfectly. There are a wide variety of O-ring port  to -AN adapters available from all major fitting manufacturers.
No PTFE or sealant is used on the threads of these fittings because the O-ring is doing all of the seal work, not the threads. We always highly recommend lubricating the O-ring with a small amount of engine oil before assembly. This helps prevent damage to the O-ring during tightening of the fitting.

Here is an example of a fuel pump with O-ring ports:

Photo Courtesy of Car Craft Magazine

O-Ring Port Fittings summary
Common Automotive Uses: aftermarket oil pumps, catch cans, fuel rails, fuel pump ports
Benefits: Positive seal, wide variety of adapters available, easily serviced, suitible for high pressures, replaceable sealing element,  very robust connection, easy to disassemble.

Drawbacks: None

There are more connections used in the automotive industry, but these are the ones that are dealt with the most by autmotive builders and enthusiests. Understanding what products to use and how to properly use them will result in a leak-free reliable connection. If you are unsure, contact us for assistance or consult with your builder.