2025 Q4 Review - Impreza STI Hatchback

As winter approached, the pressure was on to finish and to run in the 2.1 litre engine. The final engine assembly went as planned, with the vapour blasted cam covers (by local specialist DC Customs) looking great.

After fitting the engine, it was then time to alter the wiring loom to accommodate the reluctor type of crank sensor - which is different to the optical type of cam sensor used as standard on the STI hatchback Imprezas. After some head scratching, inspecting the voltage traces from the Link G4X's built in oscilloscope, and talking to Link's helpful and patient helpdesk, the wiring was completed such that the ECU received the correct signals for it to sync the engine position.

After replacing a faulty spark plug coil, the engine was running as it should, and after a quick mapping session, it was time to run the engine in over 1000 miles. This was undertaken via some short local journeys and some longer distance trips. Care was taken for the engine revs not to exceed 3500 RPM, and a tentative right foot ensured that the VF48 turbo would not produce much positive boost. After replacing the oil at 500 miles (which contained the characteristic light metallic swarf), the running in was completed without mishap.

The hatchback's new exhaust was great, without the previous drone at motorway speeds, but keeping the characterful Subaru rumble for when a tunnel approached. All too soon the running in mileage was completed and the 2.1 removed from the car for a final check over before being placed for sale! At the time of writing, the engine is nearly ready for its valve shim clearances check, and will be up for sale in early 2026! The next engine for the hatchback is a closed deck 2.5 with twin AVCS heads, and the plan is to have the hatchback back on the road before a trip to the Nürburgring in the summer of 2026. Stay tuned for more updates!