I don't know why you would want tgv valves anyways go look around the wrx forums its one of the common things to remove from the car when modding it. So not sure how this could be a performance increase. Now the changes to the direct injection could make a little difference mainly the chirping noise but it doesn't really bother me. Doubt it will give any notable HP gains.
http://forums.nasioc.com/forums/show....php?t=1663677
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