Sizing 13B injectors and fuel pump flow
A 13B rotary can consume fuel quickly once boost and engine modifications raise output. Injector and pump sizing still begins with the mass of fuel required at the hardest operating point. Peak power alone does not reveal fuel pressure, injector duty cycle, hot-soak losses or the difference between street and track calibration.
This guide covers a practical sizing process for 13B builds, from fuel demand to pump curves and ECU commissioning. Australian conditions include RON 91, 95 and 98 petrol, variable E10 availability, the Australian parts market and imported rotating assemblies.
Set the fuel target before choosing parts
Choose a realistic target output, redline and operating profile before selecting hardware. A 13B making 200 kW on the street can differ greatly from a 280–300 kW track build. Establish a rich, temperature-safe target lambda for the planned boost and fuel, and record the airflow measurement used to set it.
The most useful calculation starts with dry-air mass flow. Required fuel flow equals measured air mass flow divided by target mass AFR; required injector flow equals that fuel flow divided by the maximum permitted duty cycle. For example, a 300 kW combination pulling 820 kg/h of air at an AFR of 13.0 needs about 63 kg/h, or 139 lb/h, of fuel. At a 75% duty target, every injector must deliver at least 185 lb/h at its working differential pressure. A 70–80% maximum duty leaves useful margin for battery voltage, ageing and heat.
Before ordering, identify the injection layout, pump locations, regulator type and connector pins. Treat the factory service manual as the baseline, then use NARMADI resources as a second source for model-specific diagrams and archived information. Australian builds can combine RHD bodywork with Japanese- or North American-based drivetrains, so verify connectors and sensor polarity. Used-vehicle imports may require BICON biosecurity clearance, while GST and customs charges on parts can affect the budget.
Match injectors to differential pressure
Injector flow ratings are pressure-specific. A 300 or 400 lb/h headline figure is measured at a stated differential, commonly 3.0, 4.0 bar or more. The relevant number is rail pressure minus cylinder pressure. A manifold-referenced regulator can hold roughly 3 bar across the injectors; a returnless regulator referenced to atmosphere sees less differential as boost rises. Log rail and manifold pressure together.
Use manufacturer curves to find flow at the pressure the system will maintain; never order from the nominal label alone. A high-pressure-rated injector can deliver much less at a lower differential. Larger injectors also need longer energised time, so confirm ECU dead-time compensation, driver limits and voltage behaviour. Check minimum battery voltage at the ECU and relays, because a 14 V bench result will not represent a hot, idling starter.
Exhaust backpressure can depress fuel pressure under boost if pipe diameter or muffler restriction is mismatched to turbine flow. Verify the turbine and downstream exhaust can pass the intended volume; the cat-back sizing guide covers the relevant pipe and muffler choices. Australian catalyst, noise and emissions requirements also constrain the final street exhaust configuration.
Match pump output at working pressure
Fuel-pump capacity must be judged at working pressure, not from the casing’s free-flow figure. The high-pressure pump should cover peak demand while maintaining regulated pressure, and a return-type system must also provide bypass flow. The lift pump has a separate job: keeping the high-pressure pump flooded while overcoming tank lift, filter restriction and line losses.
| Component | Rating to verify | Sizing basis | Operating check |
|---|---|---|---|
| Injector | Flow at working differential | Fuel demand divided by maximum duty | Manufacturer curve and ECU pulse width |
| High-pressure pump | Delivered flow at rail pressure | Above peak demand | Hot fuel, voltage and filter loss |
| Lift pump | Free flow at lift height | Feed demand plus system losses | Pickup, return capacity and tank venting |
| Regulator | Differential at the manifold | Stable pressure hot and under boost | Bypass capacity and temperature drift |
Convert demand into the units used by the pump curve. At 63 kg/h, gasoline’s density of about 0.74 kg/L means roughly 85 L/h before losses. A catalogue figure well above that can still collapse at 3–4 bar. Paired lift pumps help only when the controller, wiring and tank return path support parallel operation.
Treat hot fuel, low battery voltage and a restrictive filter as operating cases. Set the regulator so injectors see the intended differential at hot idle and full boost. On a return-type system, confirm bypass capacity and prevent returned fuel from saturating the tank. A returnless layout reduces recirculation heat but makes pump headroom and pressure control less forgiving.
Commission wiring, fuel and ECU settings
Tune for the fuel in the tank. RON 91, 95 and 98 changes ignition requirements, while E10 changes charge correction and stoichiometric ratio; configure the wideband sensor for the mixture used. Melbourne’s cool, wet winters can expose weak cold-start enrichment, Sydney humidity increases condensation, and Brisbane or Adelaide summer heat raises intake temperature and fuel-system heat soak. Those conditions justify generous pressure margin and hot-weather validation.
Before the first wide-open-throttle test, verify injector flow at pressure, regulator operation, pump voltage, grounds, relay logic and leak-free lines. Use a known-good gauge and inspect the fuel filter. If the ECU controls the lift pumps, confirm minimum battery-voltage compensation and adequate supply wiring. A pressure reading alone cannot reveal a pump starved downstream of the tank.
For Megasquirt-based 13B management, the PowerFC setup overview provides a practical sequence for base sensors, ignition, idle and fuel control. Enter the correct injector and fuel-pressure data, then establish injector pulse width from measured pressure rather than an assumed flow rate. Verify cam and crank sensing, coolant compensation and the wideband baseline. During validation, record fuel pressure, lambda, duty, timing, boost and calculated fuel mass flow. If rail pressure sags, correct the pump, regulator or restriction before changing the injector map.
Build a repeatable fuel system
The reliable sequence is to define the operating target, measure fuel demand, calculate injector and pump requirements at working pressure, then validate under load. It keeps a street 13B’s driveability separate from a race engine’s absolute output.
Create a commissioning sheet before ordering parts. Record target output, dry-air flow, target lambda, required fuel flow, maximum duty, regulator pressure, pump curve and injector-flow point, then keep those documents with the vehicle. Choose a conservative duty limit, document the operating pressure and validate under full load before adding boost.