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Fuel pump information


Here you can read more about fuel pumps. The information is divided into the following parts:

  1. Fuel compatibility
  2. Different sizes / formats
  3. Internal or external fuel pump
  4. Flow (what power the pump can handle)
  5. Back pressure
  6. Strange sounding fuel pump
  7. Check valve
  8. Connector
  9. Pre filter
  10. Fuel pump selection
  11. Bolt on fuel pump
  12. Compare fuel pumps


Fuel compatibility

Petrol, Ethanol, Methanol, Diesel
Almost all fuel pumps can handle petrol, 98octane and lower octane levels without any problems. It is when alcohol fuel such as E85 or other aggressive fuels such as high-octane racing fuel are used that problems are encountered. Gasoline thus lubricates and cares for the pump without the need for any further service. When using ethanol / E85, the problems start in different ways. The most common is that the internal parts of the fuel pumps wear down and the pump simply stop. Despite texts stating that fuel pumps can handle E85, you should be aware that they wear out wuicker than using petrol and will then have a shorter lifespan. There are very few fuel pumps that can actually run on E85 / Ethanol, where the internal components are made to withstand alcohol fuels. Regardless of the choice of fuel pump, a lubricating additive must be used when using ethanol as fuel to reduce wear.


What fuel can a fuel pump handle?

Most fuel pumps can handle gasoline unless otherwise specified. But when it comes to ethanol and racing fuel, you can run into problems. Mainly because gasoline has a natural "lubricant" for the internal components of the fuel pump that race fuel and ethanol do not.

Now you have two options. Add lubricant as an additive or use a fuel pump made for ethanol. But you better use both to be sure.

Note!. There is a difference between a fuel pump that is made for race fuel and ethanol and a regular fuel pump that can handle this fuel during longer periods.



Different sizes / formats

The most common dimensions of original and aftermarket fuel pumps that are mounted in-tank, in a fuel pump fitting inside the fuel tank, are 39mm, 40mm, and 50mm. There is also an extra small Walbro fuel pump (GST302) which measures only 36.5mm in diameter.

As an external fuel pump, there are primarily pumps 60mm in diameter and a small Walbro pump of 39mm.



Internal or external fuel pump

What determines whether you should use an external or internal pump is the mounting options. The function is the same as long as the specific pump you are looking at can handle the flow.

If you have a fuel tank that does not allow for the installation of an internal pump, use an external one. But an internal fuel pump can usually be used as there are now more small, good pumps that deliver good flow.



Flow (what power the pump can handle)

How much flow must the pump handle?
To know this, you have to calculate how much fuel will be used if the fuel injectors are fully open. Do we have, for example, a 4cyl turbocharged engine with Bosch 1500cc injectors that should use 1 bar of boost with 3 bar basic fuel pressure.

With a linear fuel pressure regulator, the fuel pressure will then be 4 bar at full boost pressure. A 1500cc Bosch fuel injector flows 1690cc per minute at 4 bar which is 6.76 liters per minute. This multiplied by 60 (one hour) is 405.6 liters of fuel per hour which will be needed at full boost pressure.

A fuel pump flow better when worn in. Measurements between 5-20% have been made after a period of time.


How much power a fuel pump can handle

Deciding which pump to use to handle your power goals needs some simple calculations. Example:

4 x 900cc/min injectors at 3 bar.
900 x 4 = 3600cc/min (3,6L / min)
3,6 * 60 = 216L/H (fuel pump capacity at 3 bar back perssure)

If you run 1 bar overpressure and the injectors deliver 960cc at 4bar.

4 x 960cc/min injectors at 3 bar.

960 x 4 = 3840cc/min (3,84L / min)
3,84 * 60 = 230,4L/H (fuel pump capacity at 4 bar back pressure)

Be sure to check the fuel pump flow at your calculated back pressure. You can do this easily using the tags in the category here:

Fuel pumps


Fuel pump flow drop when pressure increase.
Injector flow increase when pressure increase.

Max pressure

Injection or carburetor
Here it is really a question of whether you should have a high-pressure pump for the injection system that can deliver up to 9 bar pressure, as some motorsport fuel injectors can handle up to 8 bar pressure. Alternatively, a low-pressure pump that usually delivers up to 0.5-0.6 bar.




Back pressure

The fuel pump name is often given by the fuel flow they can deliver at 3 bar. This give you an indication of what you need. Compare it to a bicycle. With a high gear, you can go faster = the pump max flow. But with a higher gear it becomes harder to go uphill = fuel pump back pressure.

Be sure to check the fuel pump flow at your calculated back pressure. 3 bar base pressure plus 1.5 bar charge pressure gives you 4.5 bar back pressure.

This information determines how much power a pump can handle.



Strange sounding fuel pump

Various reasons why the fuel pump sound strange:

Different pumps sound very different
Different fuel pumps can make different noises / in different ways. Even identical fuel pumps of the same make and model next to each other can sound different.

There is air in the system
The fuel pump is mounted so that air enters the line. When air enters the system, the fuel pump will sound different. Air can get in if the pump sits above the fuel level / high up. Fuel pumps are not made to drag the fuel. Then should be feeded.

Clogged pre-filter
When the pre-filter is clogged, the same phenomenon occurs as when there is air in the system, and thus the fuel pump will sound different. There may also be a built-in filter in the pump that may be clogged and block the flow.

Increased fuel pressure
When the fuel pressure increases with the boost pressure, the pump also changes sound with the load. This is completely normal and applies to all fuel pumps even if no difference is heard.

Clogged fuel filter
The fuel filter may be clogged. This corresponds to increased fuel pressure. The fuel pump has to work harder to push the fuel through with a different sound as a result.

Deposits from Ethanol
When you use ethanol, deposits form - even if the car is just standing still. These deposits form more easily if the car is stationary. When the fuel is replaced, there are usually not as many problems with deposits. Fuel additive for ethanol is always recommended! When deposits form, the fuel pump usually sounds different for various reasons. Some reasons are that the fuel filter, pre-filter and lines become clogged.



Check valve

Non-return check valves are available in different designs and the ones that are talked about in the aftermarket are the Bosch variant which cannot handle high flow but which seals very well. Then there is a full-flow non-return check valve that have larger body design than a normal check-valve in order to accommodate the internal components without obstructing the flow. These full-flow check valves are basically always used in aftermarket systems when you want flow but still the characteristics of an original car that is easy to start.

Check valves are used when you want to maintain the fuel pressure even when the engine is switched off to make it easier to start. These check valves are mainly used in fuel systems where two or more pumps are run in parallel in different steps. This is so that fuel is not forced out the back through the fuel pump which is switched off.




Connector / terminal on fuel pump
The terminals and connector on fuel pumps usually differ depending on the brand. Walbro has one version, Bosch has another, etc. When you look at external pumps, they almost always have terminal connections.



Pre filter

External fuel pump
Fuel pumps have built-in fuel filters (pre filter) that are mounted internally and cannot be replaced. This is not counted as a filter. If you want a fuel filter, you buy it separately and put it on the pressure side. If you want a pre-filter, you also buy this separately and mount it before the fuel pump on the suction side (inlet).

Internal fuel pump
Here the pre-filter is mounted on the suction side / inlet of the pump and can easily be replaced by clicking off the old filter and clicking on the new one. This assumes that you not have the pump assembled.

Read more about fuel filters here



Fuel pump selection

Choose fuel pump in 3 easy steps

These are only simplified guidelines. You want slightly bigger injectors than needed because you do not know exactly what power you should have or because there are no injectors available in such small steps that match your power exactly.

Therefore, the fuel pump now also becomes a bit too big as we match it to the flow of the injectors. The reason is that if you later have more power and calculate what the injectors can handle, the fuel pump may not be big enough.

But with this method, the injector and fuel pump are matched.

Step 1
Find what injectors to use here
Step 2
In the blelow list - find out how much the injectos you should use flow. (4,5,6 or 8 injectors)

4 injectors

280cc - 67 l/h
373cc - 90 l/h
430cc - 103 l/h
550cc - 132 l/h
630cc - 151 l/h
870cc - 209 l/h
980cc - 235 l/h
1200cc - 288 l/h
1500cc - 360 l/h
1700cc - 408 l/h
2200cc - 528 l/h

5 injectors

280cc - 84 l/h
373cc - 112 l/h
430cc - 139 l/h
550cc - 165 l/h
630cc - 189 l/h
870cc - 261 l/h
980cc - 294 l/h
1200cc - 360 l/h
1500cc - 450 l/h
1700cc - 510 l/h
2200cc - 660 l/h

6 injectors

280cc - 101 l/h
373cc - 134 l/h
430cc - 154 l/h
550cc - 198 l/h
630cc - 227 l/h
870cc - 313 l/h
980cc - 353 l/h
1200cc - 432 l/h
1500cc - 540 l/h
1700cc - 612 l/h
2200cc - 792 l/h

8 injectors

280cc - 134 l/h
373cc - 179 l/h
430cc - 206 l/h
550cc - 264 l/h
630cc - 302 l/h
870cc - 418 l/h
980cc - 470 l/h
1200cc - 576 l/h
1500cc - 720 l/h
1700cc - 816 l/h
2200cc - 1056 l/h

Step 3
Choose the pump that flows at least as much as the value you obtained in step 2.

Model - liters/hour

Bosch  0 580 254 040 - 210 l/h
Walbro GST 302 - 240 l/h
Walbro GSS 342 - 255 l/h
Walbro GSS 341 - 255 l/h
Walbro GSL 392 - 255 l/h
Bosch 0 580 254 044 - 260 l/h
AEM 320L E85 - 320 l/h
AEM 320L - 320 l/h
Fuel pump E85 silver - 340 l/h
Fuel pump E85 black - 340 l/h
DeatschWerks DW400 - 400 l/h
AEM 400L 420 l/h
Walbro GST 450 - 425 l/h
Walbro GST 520 - 470 l/h

Increased fuel pressure: Fuel pump flow drops and injector flow increase.
Reduced fuel pressure: Fuel pump flow increases and injector flow decrease.



Bolt on fuel pump

When you have found the minimum flow your fuel pump should have, it is time to see which pump fits physically in size. The question often is: "which pump is bolt-on". The only thing we know that is "bolt-on" is original, otherwise there is often a difference between the OEM and the pump that can handle the flow you need. Even if the pump does not fit directly, it is usually quite easy to adapt the fuel pump hanger to fit the new pump.

Both connections, diameter and length of the fuel pump can be adapted using an adapter or hose so installation can be done in a simple and good way. We usually say that 99% of the fuel pump hangers need minor adjustments to fit the new upgraded fuel pump.

The assembly is relatively simple, so we usually also say that the 99% who have to modify the holder do not need to change much for it to work.