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The recommended replacement interval for the cam belt was 100,000 kms or four years, whichever occurred first. A self-adjusting, hydraulic tensioner maintained timing belt tension and valve clearance checking/adjustment was only necessary every 150,000 kms.

AVCS: GD.II/GG.II Impreza WRX

For the GD.II/GG.II Impreza WRX, the EJ205 engine had Subaru’s ‘Active Valve Control System’ (AVCS) which adjusted the opening and closing timing of the intake valves by changing the phase angle of the camshaft sprocket relative to the camshaft; for the GD.II/GG.II Impreza WRX, it is understood that the maximum range of adjustment was 35 crankshaft degrees. Under the control of the ECM, an oil flow control valve would move its spool to switch the hydraulic passage to/from the advance and retard chambers in the camshaft sprocket to vary the phase angle between the camshaft sprocket and camshaft.

Based on input signals from the air flow sensor, engine coolant temperature sensor, throttle position sensor and camshaft position sensors, the engine control unit could use three computer maps to achieve the following -

Optimum valve timing for stable idling: minimal intake and exhaust valve overlap);
Improved fuel consumption at medium engine speeds and low loads: intake valve timing was advanced to reduce intake air blow back and improve fuel consumption. Furthermore, increasing intake and exhaust valve overlap enhanced exhaust gas recirculation (EGR) for a reduction in NOx emissions. When engine load increased, advancing the intake closing time utilised the inertia of the intake air to create a supercharging effect; and,
Maximum power at high engine speed and load: intake valve timing was further advanced to maximise overlap and utilise the scavenging effect produced by exhaust gas pulsations to draw intake air into the cylinder. Since the intake valve was closed at the end of the intake stroke, air intake efficiency was improved and power increased.

The intake ports for the EJ205 engine were designed to create a ‘tumble swirl’ air motion as the air and fuel entered the cylinder - this action improved mixing of the air and fuel for more uniform flame travel and faster combustion. According to Subaru, the tumble swirl intake ports enabled maximum gas pressure (downward force) to be applied to the piston 10-15 degrees ATDC when the maximum turning moment on the crankshaft occurred, resulting in a greater power output.

For the GD/GG Impreza WRX (October 2000) and the SF.II Forester GT (December 2000), Tumble Generator Valves (TGV) was introduced for lower exhaust gas emissions at low speed cold engine conditions. Specifically, the TGV worked by closing a butterfly valve in the intake manifold to create a tumble air motion at low intake air speeds, thereby improving air/fuel mixing for improved combustion efficiency and emissions.

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