A whole lot!!1 Had to hack a ton off the front bumper cover along the bottom to keep it from bulging out. The fender lining was almost completely cut out to accommodate the driver-side charge pipe. I actually tossed a few of the pipes that came with the kit and rearranged them. The turbo-intercooler pipe runs over the top of the motor rather than underneath it like the directions say. It's a couple less bends and clamps. It also looks better in my opinion. Only major problem was the pipe that connects to the inlet of the intercooler on the driver side. It doesn't fit AT ALL. There's about a 160 degree U-bend in the pipe that's supposed to run through a slot in the chassis, normally on the WRX. That slot is too far aft on the GC and I need to get that pipe custom made. In the second pic, you can see how the pipe hangs down. Luckily, it's high enough to not scrape.