H22A Prelude Engine Swap into an EG Civic

Remove the bonnet, both front fenders, the front bar, the front suspension, the radiator, the battery, driveshafts, brakes and A/C (if fitted) - essentially everything surrounding the engine and gearbox. Critically, before disconnecting anything electrical, mark every connector with tape and a marker at both ends of the connection (engine-harness side and ECU side). This labeling is what makes reassembly and harness adaptation manageable.

Remove the remaining brackets and pumps, then loosely support the engine with the crane, remove the mounts, take the weight and lift the old engine and gearbox out. Remove the complete exhaust system: the Prelude headers are much longer than the original Civic ones, so the entire exhaust must come off and be replaced with a system built for the new engine.

With the bay empty, this is the time to respray it if desired (this one was painted black); otherwise a thorough clean is sufficient. The Hasport mount kit requires cutting off the driver-side gearbox mount below the suspension tower. If you want to keep power steering, either cut a scallop out of the body near the passenger headlight for pump clearance, or use a 1997-on Prelude pump and bracket which clears without cutting. When cutting the scallop with the engine already in the car, cover the engine completely so metal filings cannot get into the fresh install.

Fit the Hasport rear mount bracket to the engine before installing it - it is much easier out of the car. Rather than lowering the engine in from above, jack the car right up and roll the car over the engine; lining up the mounts is much easier this way. Bolt all mounts loosely into place and leave final torquing until later.

Reuse the standard Civic engine harness and adapt it to the Prelude engine. Extend the alternator power wire, and change the injector clips and extend the injector wires. If you retain the stock H22A peak-and-hold injectors you MUST wire in the injector resistor box: each H22A injector clip has one colored wire and one black wire. Solder the four colored wires to the original colored injector wires in the Civic harness. Join the injector clips' four black wires to the resistor box's four wires (order does not matter), then tap the resistor box's red wire into a switched 12 V ignition feed.

Add three wires for the O2 sensor and change to the Prelude O2 sensor connector, then wire as follows (OBD1 Civic ECU): WHT to the WHT/RED wire at pin D14 (O2 sensor input); BLK to the ORG/BLK wire at A6 (heater control); GRN to the GRN/WHT wire at D22 (sensor ground); BLK to the YEL/BLK wire at A25 (sensor voltage - alternatively splice into the power junction at the driver-side shock tower harness).

There are two spare slots in the driver-side shock tower harness connector; salvage one male and one female pin out of an unused plug and add them for a factory-look connection. Run a wire from the VTEC solenoid's GRN/WHT to ECU pin A4. Run the VTEC oil pressure switch (BLK/BLU) to pin D6, and solder-splice its second wire (VTEC oil pressure ground) into the engine harness's thermostat ground. For the knock sensor (which sits near the cylinder head at the engine's rear), use the one remaining spare shock tower slot the same way and wire it to pin D3 (OBD1).

For the air intake bypass solenoid - the secondary butterflies - run sensor voltage to A25 (or splice into the YEL/BLK wire at the driver shock tower harness) and the ECU signal to A17. EGR system: lift valve solenoid takes sensor voltage from A25 with its ECU signal to A11; the lift sensor takes sensor voltage from A25, ground from D22 and its signal to D12. Only wire the EGR if you are running a P13 ECU - a P28, P72 or similar ECU does not look for EGR, so the wiring would be wasted effort. With the harness complete, fit it to the engine; extending wires to length is easier with the engine already in the car.

Civics and Integras shift via rods, while Preludes use cables, so the shifter opening in the tunnel must be cut larger to accept the Prelude cable shifter assembly. Transfer the Civic reverse light switch from the old gearbox to the H22A box - they are exactly the same and it works directly. Use the Civic clutch slave cylinder rather than the Prelude one due to clearance: it is a straight bolt swap needing only one hole drilled in the bracket.

Install the alternator, power steering pump, reservoir and all brackets (after the clearance scallop is cut if applicable). Fit the radiator and thermo fan. For fuel, have a hose specialist fabricate the line from the fuel rail to the filter, or modify the original Prelude line to fit as was done here; fit the uprated in-tank pump. A standard EG aftermarket intake pipe and pod filter fits the H22A throttle body. Install the headers and torque them to specification.

The Hasport driver-side shaft is a complete assembly and installs directly. On the passenger side, install the H22A intermediate shaft first; the Hasport shaft then fits straight into it.

Refit the front suspension and brakes, then set the car back down on the ground. Upgrading suspension and brakes is strongly recommended for the extra weight and power: this build used Koni adjustable shocks all round with Integra front super-low springs, stiffer custom rear springs, and a rear drum-to-disc conversion using Integra SiR-G rear discs and calipers. Also consider ground clearance: with the H22A's sump and header height, clearance is acceptable on 17-inch wheels but very poor on 14s, so factor wheel and tire choice into the build.

Fill all fluids and bleed the brakes and clutch. Plug the ECU into the main harness, then start the engine. If the check engine light comes on, switch off and read the fault code: bridge the 2-wire service connector under the glovebox (the one nearest the door, sitting in the rubber housing) with a piece of wire, turn the key on without starting, and count the flashes - one long flash equals 10, each short flash equals 1. Verify every vacuum line is connected. Finish with a properly made exhaust system and have the swap certified/engineered as required.