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Phase 1 vs Phase 2 Subaru Engine Basics

In this blog post we go over the differences between phase 1 and phase 2 Subaru engines. If you are looking to replace a blown engine, click here.

What is Phase 1 and Phase 2?

Phase 1 and Phase 2 refer to the year the engine was made. There are also some mechanical differences.


Phase 1

Years Made: 1998 and older engines

Tuneable ECU: None

Intake Manifold Bolt Pattern: Straight Line Pattern

Phase 2

Years Made: 1999 to current engines

Tuneable ECU: Many but not all

Intake Manifold Bolt Pattern: Offset Pattern

Why does it matter?

The most important thing to know is that phase 1 and phase 2 engines are NOT interchangeable and must be a matching pair.


The common request in this regard is a tuneable ECU for a phase 1 engine.

If the car has a phase 1 engine and a phase 2 ECU is desired, then a phase 2 engine and ECU must be wired in. If the car is phase 2 and a phase 1 engine is desired, then a phase 1 engine and ECU must be wired in.


For a basic replacement engine swap (IE non turbo to non turbo) we would typically suggest taking all of the parts off the original engine and putting them onto the new long block. The problem is to do this the main timing cam gear (below the oil filler), crank sprocket, and intake manifold with harness would need to be swapped. However, the parts won't physically attach to each other due the difference in bolt patterns from the manifold to the head, and cam gear design.

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