In 2008, Subaru moved the Impreza over to the Legacy chassis and made a few changes under the hood for the first new model WRX but retained the smaller TD04 turbo for 2008 before moving to a bigger VF52 for the 2009-2014 models.  This range of WRXs share a lot of compatability and the VF52 is a direct bolt-on for the 2008 model.