For those who wish to calculate mass flow themselves, we offer the following formula:

F2 = (√P2/√P1) x F1

F2 = New flow rate (lbs/hour or cc/min)
F1 = Old flow rate (lbs/hr or cc/min)

P2 = New Pressure
P1 = Old Pressure

Example: We have an injector rated to flow 315cc/min at 43.5 psi (3bar). That combination does not flow enough fuel to reach our desired output. So, we wish to determine how much will it flow at 58psi (4bar):

F2 = (√58 / √43.5) x 315
F2 = (7.616 / 6.596) x 315
F2 = 364cc/min

For those who wish to calculate mass flow themselves, we offer the following formula:

F2 = (√P2/√P1) x F1

F2 = New flow rate (lbs/hour or cc/min)
F1 = Old flow rate (lbs/hr or cc/min)

P2 = New Pressure
P1 = Old Pressure

Example: We have an injector rated to flow 315cc/min at 43.5 psi (3bar). That combination does not flow enough fuel to reach our desired output. So, we wish to determine how much will it flow at 58psi (4bar):

F2 = (√58 / √43.5) x 315
F2 = (7.616 / 6.596) x 315
F2 = 364cc/min

Injector Spray Patterns

Factory engineers have gone to great lengths to make sure that fuel is injected in the correct spray pattern for each cylinder head design. Meanwhile, tuners have put up with cold start problems, lumpy idles, misfires and other problems for years. A major reason for this is injectors that are mismatched to the application.

The picture on the left shows a 16v inlet port in detail. A central bridge is clearly visible. This is where the main inlet port becomes split to direct air (and fuel) towards the intake valves. The correct injector type for this inlet configuration is one where the injector nozzle sprays precisely-split fuel streams directly into each port and onto the back of each inlet valve.

Contact with the metal walls is carefully avoided. An injector that sprays a single-narrow fuel cone will wash down the manifold and head. Tuning/holding precise air/fuel ratios is thusly complicated because fuel puddles and then slowly dribbles into the combustion chamber. So much for EFI precision!

Crossflow 8v and VR6 12v are more easily taken care of with conventional injectors. Fuel is atomized after impact with the valve itself or, better yet, directly at the injector tip.

Click to download injector videos (400kb - 1.5MB).

Engines are not generic. Neither are fuel injectors.

Injector Impedance:

It is also important to understand that fuel injectors come in two electrical flavors -high and low-impedance. VW ECUs require high-impedance but many standalone systems are equipped to manage the lows. The primary advantage of low-impedance injectors is their faster response time. (That is, the speed at which they can be turned on/off.) When very large injectors (e.g. >580cc) are fitted, low-impedance injectors are much easier to tune for proper idle quality and for use at extremely high rpms. The primary advantage of high-impedance injectors is the fact that less heat is generated in the drive circuit and thusly less complex/expensive circuitry is required. Again, if you have a VW ECU you absolutely must use high-impedance parts.

USRT offers fuel injectors for many engines. Non-VW/Audi options are available by special request. Please consult with us for fitment details.

Know Your Needs:

In order to determine what kind of fuel pump will take care of your engine's needs, you must first decide on (or know) the injector size and the maximum boost you plan to run. For example, an (AWP-code) 1.8T’s stock 317 cc/min injectors might require an upgrade to 580cc/min injectors. Four 580cc injectors theoretically will flow 139lph at 100% injector duty cycle (IDC). A boost pressure of 25 psi would probably be considered by many to be the upper limit for most street engines. The fuel pump you need then must be able to supply at least 139lph at 68.5psi fuel line pressure (43.5psi base pressure + 25 psi to compensate for boost pressure in the plenum) at the voltage the pump is receiving. The voltage the pump receives is critical because flow can vary by 5 to 80 percent per volt depending on the particular pump, the voltage level, and the line pressure.

Get the Ratings:

To determine if a fuel pump can meet your needs, you will need either a flow chart (see the example below) or a flow rating for the pump. A flow chart is the best choice because it shows the measured flow rate over a range of line pressures, usually in increments of either 5 or 10 psi, for a particular supplied voltage. A flow rating cites the flow rate at one line pressure. For a flow rating to be useful it also must state the supplied voltage. If the voltage is not stated, it is probably fair to assume it is 13.5 volts. The flow rating pressure is usually 0 psi (also called the free-flow rating) or some integer multiple of bars. Three bars (43.5 psi) is a popular rated pressure for electric pumps, as is 5 bars (72.5 psi).

USRT recommends a program called "convert.exe" to juggle the metric and standard measurements that are required to do these sorts of calculations:

Download

Use our precision-fabricated adaptors to fit stock fuel pressure regulators for an inexpensive and OEM-clean set up.