10th Gen Civic Port Injection Kit Installation and Tuning

10th Gen Civic Port Injection — Why It Matters

The L15B7 direct injection system reaches its limit around 360–400 wheel horsepower depending on fuel. At that point, the high-pressure Fuel Pump runs out of capacity, injector duty cycle hits 100%, and ethanol content compounds the problem because ethanol requires roughly 30–40% more fuel volume than pump gasoline. Port injection solves this by adding independent fuel delivery through injectors mounted in the intake manifold adapter plate, supplementing the stock DI system rather than replacing it.

A secondary benefit is reduced carbon buildup on intake valves. Direct injection engines accumulate deposits on the back of the intake valves because there is no fuel spray to wash them. Port injection reintroduces that cleaning effect, which on high-mileage L15B engines can meaningfully extend valve service intervals.

The goal of this guide is to cover every kit option, the Split Second controller that makes them work, injector and fuel pump sizing, installation steps, wiring, tuning, and the gotchas that owners encounter on the 10th gen Civic platform.

Available Port Injection Kits

Three primary options exist for the 10th gen Civic 1.5T: PRL Motorsports, MAPerformance, and TwoSix Auto (VCD Racing). Each takes a different approach to what is included versus what the owner sources separately.

All three kits share the same architecture: a billet aluminum adapter plate that installs between the intake manifold and cylinder head, injector ports machined at a specific spray angle, and a CNC-machined fuel rail with -8AN ORB female ports. None of them replace the factory DI system. The PRL and MAP kits expect the owner to supply injectors, controller, wiring, AN fittings, fuel hose, and a fuel source. The TwoSix Auto kit is the only true plug-and-play option that includes every component.

PRL Motorsports Port Injection Kit

PRL designed the HC10-PIK around Bosch EV14-style 48mm top-feed injectors with 14mm upper and lower O-rings. This covers Injector Dynamics (ID1050x, ID1300x, ID1700x), Deatschwerks (17U-00-0050 through 17U-00-0095), and Fuel Injector Clinic (IS151-0650H through IS151-1650H) injectors. The billet 6061 adapter plate is anodized, the fuel rail has three -8AN ORB female ports plus one 1/8-inch NPT port for a damper or sensor, and all stainless hardware is included.

The notable downside is the charge pipe issue. Because the adapter plate adds roughly 10–12 mm between the intake manifold and the head, the stock charge pipe to throttle body coupler is too short. PRL originally stated they were working on a solution, but as of 2025, no dedicated coupler has been released. Owners run a longer silicone coupler section or a custom charge pipe to bridge the gap.

PRL also designed the kit around use with a Radium Engineering fuel damper or similar, which helps smooth pressure pulses in the fuel rail AT higher flow rates.

MAPerformance Port Injection Kit

The MAP kit (HDAX-PIA) uses a CNC 6160 billet spacer with adjustable injector height — it accommodates both 48mm and 60mm injectors via interchangeable spacer sets included in the box. This is a meaningful advantage for owners who want to run larger-capacity 60mm injectors like the Deatschwerks 16S-12-2200 without needing a separate adapter.

The kit comes with two sets of stand-offs and bolts — short for 48mm injectors (M6x1.0x40 bolts), long for 60mm injectors (M6x1.0x50 bolts) — plus M8x1.25×70 bolts for the adapter-to-head mounting, four head-flange O-rings, a -6AN to -6ORB male fitting, and a -6AN ORB plug for the unused rail port. Injectors are not included. The fuel rail uses a single -6AN feed port with one plug, so the owner must buy the appropriate AN fittings, fuel hose, pump, and regulator to complete the system.

MAP also offers a separate fuel pump install kit (HDAX-FPIK, $99.99) that provides a billet pump mount, strainer, Wiring Harness, and bulkhead for a Walbro 450-sized pump, and a fuel feed line kit that replaces the restrictive OEM feed line between the tank and HPFP.

TwoSix Auto / VCD Racing Full Port Injection Kit

The TwoSix Auto kit is the only complete solution sold as a single purchase. For $1,946 it includes the adapter plate and fuel rail, four 1000cc injectors, a 340LPH E85-compatible in-tank fuel pump, -6AN PTFE fuel lines, -8AN plugs and feed line, a -6AN split-T fitting, and a Split Second fuel controller. VCD Racing (the developer behind the kit) published results showing 456 wheel horsepower on their 10th gen Civic Si shop car, with an additional 100 wheel horsepower attributed specifically to the port injection system compared to running on DI alone.

The kit is compatible with the Skunk2 Ultra Street intake manifold if the owner contacts TwoSix directly for the appropriate fuel rail configuration. Full installation instructions are included with the kit.

Injector Controller — Split Second AIC

The Split Second Additional Injector Controller is the standard piggyback unit used across all 10th gen Civic port injection setups. It is an independent controller that reads engine load and RPM to determine when and how much fuel to add through the port injectors. It does not communicate with the stock ECU — it operates as a standalone fueling layer on top of the DI system.

Three AIC variants are relevant to the L15B platform:

The AIC1-V4H w/4-channel tach is the most common choice for L15B port injection builds because it was designed specifically for direct-injected four-cylinder engines. Each of its four tach input wires connects to the trigger signal wire on one ignition coil. The controller uses these signals to derive true engine RPM, which it combines with the voltage input from a MAP or MAF sensor to determine the appropriate fueling. The unit uses a 0-5V input range and is compatible with the stock MAP sensor signal.

The controller programs via the R4 engine management software over a serial connection (USB-to-serial adapter required on modern laptops). Map data is stored in .bin files; definition .xdf files configure the user interface. The controller ships without a pre-loaded map, so loading a base calibration before running the engine is mandatory.

For wiring, the pinout on the AIC1-V4H harness is:

• Pins 1-4: Individual ignition coil trigger inputs (one per cylinder, connects to the trigger wire on each coil pack)
• Pin 6: Switched 12V ignition power (use an add-a-circuit fuse tap)
• Pin 7: Ground
• Pin 8: MAF or MAP signal (0-5V input)

The injector harness connects directly to the port injectors with EV1 or EV6 connectors (specified at purchase).

Injector Selection and Sizing

Port injector sizing depends on target power and fuel type. The port injection system supplements the DI system, so the port injectors do not need to handle the engine’s full fuel requirement. A common strategy is to run the DI system to roughly 70-80% duty cycle and let the port injectors handle the remainder. For an L15B targeting 400-450 whp on ethanol, 1000cc port injectors are sufficient. For builds targeting 500+ whp, 1300cc to 1700cc injectors provide headroom.

All listed injectors are Bosch EV14-core high-impedance (12-16 ohm) units compatible with the Split Second AIC drivers. The AIC1-V4H drives high-impedance injectors only — low-impedance injectors require inline resistors or a different controller.

The forum recommendation from experienced builders is to start on the smaller side if uncertain. A 1000cc or 1050cc injector produces a finer spray pattern and is easier to dial in at low duty cycles than a 2000cc injector. Oversized injectors at low pulse widths create idle and light-cruise tuning challenges because the controller is working at the bottom of its resolution.

Fuel System Upgrades

Adding port injection increases total fuel demand. The stock in-tank fuel pump on the 10th gen Civic is rated at approximately 155 L/hr at 70 psi (based on OEM pump specifications). At 360+ whp on ethanol, that pump cannot maintain adequate pressure, and datalogs show rail pressure dropping under sustained load.

Fuel Pump Options

The Walbro 450 requires a wiring hardwire kit because the stock pump wiring and fuse are insufficient for the higher current draw. The DW300c is a closer match to stock power requirements and does not always require a dedicated relay, though a hardwire kit is still recommended for safety margin.

MAPerformance sells a separate fuel feed line kit (approximately $180) that replaces the restrictive OEM feed line between the fuel pump hat and the high-pressure fuel pump. In their testing, the OEM feed line caused an 8 psi pressure drop at the HPFP inlet, and replacing it restored stable rail pressure under load.

Installation Walkthrough

The procedure breaks into five phases: intake manifold removal, adapter plate and fuel rail installation, fuel system plumbing, controller wiring, and charge pipe modification.

Phase 1: Intake Manifold Removal

Begin with a cold engine and disconnect the battery negative terminal. Remove the charge pipe from the throttle body and the intercooler outlet. Disconnect the intake manifold electrical connectors — MAP sensor, boost solenoid, and any PCV or EVAP connections. Remove the throttle body from the intake manifold (four bolts). Unbolt the intake manifold from the cylinder head. There are five M8 bolts securing the manifold to the head. Carefully lift the manifold off the head studs and set it aside. Clean the Gasket mating surface on the cylinder head of any old gasket material.

Phase 2: Adapter Plate and Fuel Rail

Place the adapter plate gaskets (supplied with the kit or OEM Honda intake manifold gaskets) on the cylinder head studs. Position the adapter plate over the studs. For the PRL and MAP kits, install the injectors into the fuel rail before mounting the rail to the plate. Lubricate the injector O-rings with a thin coat of assembly lube or clean engine oil to prevent tearing during installation. Seat the injectors into the adapter plate injector ports, then bolt the fuel rail into the stand-offs. Torque the adapter plate-to-head bolts to 18 Nm (13 lb-ft) in a cross pattern per Honda intake manifold specifications. Reinstall the intake manifold onto the adapter plate with the provided longer M8x70 bolts.

Phase 3: Fuel System Plumbing

Run a new -6AN feed line from the fuel pump hat (or external fuel pressure regulator, if using a return-style system) to the fuel rail. The PRL and MAP kits leave the owner responsible for sourcing fittings, hose, and a pump. A common approach is a return-style system: in-tank pump to filter to fuel rail, then a regulator on the return side set to approximately 58 psi (stock Civic base pressure). The MAP kit includes a -6AN to -6ORB male fitting and a plug for unused rail ports. The -6AN ORB plug goes on the top rail ports unless the OEM wiring harness carrier is modified to clear them.

Phase 4: Split Second Controller Wiring

Mount the AIC controller in a location protected from heat and moisture — inside the cabin near the ECU or in the glovebox is common. Run the following connections:

• Tach wires (pins 1-4): Solder each wire to the trigger signal wire on one ignition coil. The trigger wire on the 10th gen coil packs is typically the colored wire (not ground or power). Tap one cylinder per wire.
• Power (pin 6): Connect to a switched 12V ignition source. An add-a-circuit fuse tap in the interior fuse box is the cleanest method.
• Ground (pin 7): Chassis ground with a ring terminal to a clean bolt.
• MAP/MAF signal (pin 8): Tap the signal wire from the stock MAP sensor. The MAP sensor on the L15B outputs 0-5V proportional to manifold pressure.

Connect the injector harness from the controller to each port injector. Verify injector connector compatibility — order EV1 or EV6 as needed when purchasing the controller.

Phase 5: Charge Pipe Modification

The adapter plate adds roughly 10-12 mm of spacing between the intake manifold and the cylinder head. This pushes the throttle body forward by the same amount. The stock silicone coupler between the charge pipe and throttle body is too short. The fix is a longer coupler — a 75 mm to 90 mm ID silicone reducer coupler of the appropriate diameter, approximately 75-80 mm in length, replaces the stock piece. Some owners with aftermarket charge pipes that have a section of straight silicone at the throttle body end can simply slide the existing coupler further onto the pipe, but most need to purchase a longer coupler.

Split Second Controller Programming

The AIC1-V4H and AIC2 controllers require programming through a laptop before the engine runs. The process uses Split Second’s R4 software (or TunerPro RT for AIC2 units).

Hardware setup: Connect the controller to the laptop using a USB-to-serial adapter. Install the serial adapter driver and confirm the COM port assignment in Device Manager. The COM port must be set between 1 and 8 — if the system assigns a higher number, change it manually.

Open R4 software, select the correct COM port in Options > System Settings, and click Connect to ECU. Load a base .bin calibration file appropriate to the injector size and engine configuration. Split Second provides example .bin, .xdf, and .adx files for the AIC1-V4H on their downloads page.

The tuning approach for the AIC1-V4H uses a table that maps RPM against MAF voltage (or MAP pressure) to define injector pulse width. The tuner builds a fuel table that adds port injection at a specific load threshold, typically beginning when the DI system reaches 80-85% duty cycle. Below that threshold, the AIC does not fire, and the engine runs on DI alone.

A common starting strategy from the Split Second documentation:

• Set the activation threshold to come in around 10-12 psi of boost (the point where the L15B DI system begins to run out of capacity with ethanol)
• Use the RPM gain adjustment to maintain a flat air-fuel ratio as RPM climbs under full boost
• Log the combined fuel trims in KTuner or Hondata to verify the DI system is not being asked to supply more than 80% duty at the top end

The AIC1-V4H does not communicate with the stock ECU, so tuning the Split Second controller is done independently on a dyno or through wideband logging. The tuner adjusts the AIC fuel table to achieve target lambda, then trims the DI fuel table in Ktuner or Hondata to balance the two systems.

Tuning Strategy with KTuner and Hondata

Once the port injection system is installed and the Split Second controller has a base calibration loaded, the stock ECU tuning platform — KTuner or Hondata FlashPro — handles the DI side of the fuel delivery.

KTuner: KTuner on the 16+ Civic 1.5T provides direct injection fuel pressure target tables, injection phase timing access, and full flex fuel support with ethanol content adjustments for both fuel and ignition. With port injection supplementing fuel, the tuner reduces the DI fuel targets to maintain 70-80% DI duty cycle and lets the Split Second controller add the remainder. The flex fuel tables continue to account for ethanol content changes in the DI injectors, while the AIC controller is calibrated for a fixed ethanol content or adjusted manually.

Hondata FlashPro: For the K20C1 (FK8/FL5), Hondata offers a complete drop-in fuel system with 1530cc direct injectors and an upgraded high-pressure fuel pump. This system replaces the DI pump and injectors entirely and is the recommended approach for Type R builds. The kit includes a FlashPro unlock code that must be applied before the vehicle runs. For the L15B, FlashPro offers flex fuel ethanol tables and direct injection pressure controls that work alongside the port injection system. Hondata does not sell a specific port injection kit for the L15B platform — the port injection controller (Split Second) operates independently.

Boost limit consideration: The stock L15B ECU on factory electronic wastegate control has a hard boost ceiling of approximately 32.7 psi. Above that level, the ECU cannot maintain boost control through the EWG. Port injection alone does not bypass this limitation. To exceed 32.7 psi, the owner must switch to a manual boost controller or a standalone ECU such as MoTeC or Haltech.

Known Issues and Owner Tips

Split Second reliability concerns: The L15B community has mixed opinions on the Split Second controller. PRL Motorsports acknowledged it works and has been used successfully, but referred to it as a “bandaid” rather than a proper solution. The concern is that the piggyback controller operates independently of the stock ECU’s safety logic — if the AIC fails in the open position, the engine runs lean without the ECU detecting the problem. Forum reports of AIC failures at full boost exist, though they are rare. A wideband air-fuel ratio gauge with a warning output is strongly recommended as a safety backup.

MoTeC alternative: The only production-level replacement for the Split Second controller is a MoTeC standalone ECU with a custom harness. This solution costs approximately $7,000 and is appropriate only for dedicated race cars or very high-horsepower builds. For most street cars targeting 400-450 whp, the Split Second approach is the practical option.

Intake valve cleaning benefit: Owners who run port injection for extended periods report noticeably cleaner intake valves at teardown compared to DI-only engines. The port injection fuel spray washes the intake valves continuously, preventing the carbon bake-on that occurs with DI alone. This is a real maintenance advantage for daily-driven cars.

Ethanol content management: The Split Second controller does not automatically adjust for ethanol content changes. If the owner switches between pump gas and E85, the AIC calibration must be updated, typically by a tuner with R4 software access. Some owners run a fixed ethanol blend (E30 or E50) and calibrate the AIC to that specific mixture, avoiding the need for frequent adjustments.

Cost Summary by Build Tier

The TwoSix Auto kit is competitive with the DIY approach when factoring in that it includes injectors, pump, lines, and controller as a bundled package. The DIY approach offers more flexibility in injector and pump selection but requires the owner to source and assemble each piece.

☐ Port injection adapter plate bolts between intake manifold and cylinder head — does NOT replace DI system
☐ PRL kit ($260) and MAPerformance kit ($250) are adapter plate + fuel rail only; injectors and controller sold separately
☐ TwoSix Auto full kit ($1,946) includes everything: adapter plate, 1000cc injectors, 340LPH pump, AN lines, Split Second controller
☐ Split Second AIC1-V4H is the correct controller for the 10th gen — uses 4 separate tach inputs from ignition coils
☐ AIC controller programs with R4 software over USB-to-serial; base calibration must be loaded before running
☐ AIC wiring: 4 tach wires to coil triggers, pin 6 = 12V ignition, pin 7 = ground, pin 8 = MAP/MAF signal
☐ Charge pipe needs a longer silicone coupler (75-80 mm length) due to adapter plate thickness spacing the throttle body forward
☐ Fuel pump upgrade required above 360 whp on ethanol — DW300c or Walbro 450 are common choices
☐ Injector sizing: 1000-1050cc for 400-450 whp, 1300-1700cc for 500+ whp
☐ Stock ECU boost ceiling of ~32.7 psi on factory EWG — port injection does not bypass this limit
☐ Wideband A/F gauge with warning output strongly recommended as safety backup for piggyback controller
☐ Split Second does not auto-adjust for ethanol content — AIC calibration must be updated when switching fuel blends