I am certainly no expert on the matter, but I was under the impression that it would give some increase in power as it reduces some of the 'safety margins' that subaru puts in place because of the x% of consumers that do not properly maintain their cars. Things such as leaning out the air fuel ratio would give off this increase in power, but potentially at the expense of wear and tear on the engine and other parts. Alot of places will not tune older cars or enigines with 'x' amount of km's on them for this reason.
But as I said, i am certainly no expert in the matter. Everything iv just said may be entirely untrue, so do not just take my word for it. Just trying to pass on what I have heard
