Originally Posted by pleaidestar
The boxer motor is balanced very very well, it is perfectly good to run a lightweight crank pulleywith side effects or codes.
Just thought I'd chime in even though I'm a little late.
It's not actually balance that causes issues it's torsional vibration that comes from the the power stroke flexing the crank. Engines with longer strokes are more susceptible to vibration than shorter-stroke engines.
This is not an issue on Subarus because they have a relatively short stroke(even the 2.5l motors have a 79mm stroke). Though, the problem may come up with higher output cars that still run an oil pump turned directly by the crankshaft.
A great example is some of the older Honda engines(which are very reliabe, and rev pretty high). They have a 79mm-stroke B16B engine that can run without a dampened pulley just fine(you can order a lightweight one-piece "N1" pulley straight from Honda for this engine). On the other hand, it's a huge risk to run this pulley on their B18/B20 engines which have a 87.2mm or 89mm stroke; there's plenty of people who've destroyed their oil pumps with lightweight pulleys on these engines. Also, from the factory, their D15s come with a solid pulley while the D16s are dampened(84.5mm vs. 90mm stroke); even for variants with the same amount of power(D15B vs. D16Z6).
Cliffs: perfectly OK to run a lightweight pulley on our Subarus.