What is the difference between Phase I and Phase II Subaru engines?
A25: Subaru had a design update of the 4 cylinder engines around the 2000 model year introduction. Those before this change are known as Phase I, those after, Phase II. The Phase II Subaru engines feature a range of minor modifications throughout. The main ones which we are interested in here are the addition of three extra bellhousing flange bolts, and the introduction of dual mass flywheels LINK for some models. Just to make it more confusing though, it seems that not all the changes cut in at once, and although the old 2.5 DOHC had it’s cylinder heads replaced with a new SOHC design, there are also some crossover models which feature a Phase 2 crank case with Phase 1 cylinder heads.
