Cars are knocking BADLY, bone stock. There is a huge delay in the switch between open and closed loop fueling and the car runs at a stoich air/fuel ratio for a couple seconds under full boost. It is a bad, bad problem. Worse than when some of the first STI's were pinging on Cali gas. This affects every single '04+ WRX. Most people simply feel it as a flat spot in the powerband, which is the ECU pulling timing in response to the knock. Anything that helps the turbo spool quicker -- exhaust stuff, uppipe, etc -- exacerbates the problem because the car is at full boost longer before switching to open loop fueling.
By this token you would never modify anything on your car. Are you enjoying those RE-92's? Those are the tires "spec'd" by Subaru. I wonder why it puts them on nearly every single model. I bet it's because they were tested on each one and found to be the best possible tires, right? Maybe it's because the company gets a $2 discount per car when they buy xxx,xxx,xxx tires.
Maybe Subaru is using the exact same filter on our fancy turbo Legacys as it did on its 2.2 liter 1994 Impreza L. Well no, they made it skinner in '04.
Yes correct. Lets not confuse skinnier smaller and shorter smaller. As mentioned, the difference between the two Purolator Pure One filters (one being the stock filter that Subaru uses, by the way.... and you can get the Pure One's from autoparts stores for less than the stock one at a dealership, which should be no surprise) and the two Mobil 1 filters that I linked is how tall they are. They are all the same width. The manifold snakes around the side of the filter. Subaru did not change the height, they made it skinnier. No matter how tall the filter is, it has nothing whatsoever to do with its proximity to the manifold and nothing to do with how much heat it absorbs...
...actually, you could argue the taller filter gets more airflow, which would have a cooling effect. Increased oil capacity is a bonus. More filter medium means it can filter and hold more "stuff" without restriction. There is an inlet and outlet side in an oil filter just like an air filter. More surface area almost always means less restriction and longer service life.
Jeremy
The bright side is that our cars don't work filters very hard. I can't remember how many threads (dozen?) I've read with peoples' oil analysis results, but it's rare to see any breakdown before a good 8,000 miles, regardless of filter. To be completely honest, I don't think it's all that important on our cars.