Kartboy Rear Diff / Carrier Wedge Lock System

This should be the first upgrade on any WRX/STi

The Kartboy rear diff wedge/subframe bushing insert kit on my 2019 STi has changed my life. Long review warning; I'm verbose. Sorry, not sorry. I had previously installed the Perrin aluminum diff inserts and poly subframe inserts on my old '08 WRX. They were a bitch and 3/4 to install, so I had been procrastinating, expecting this to be similar. I had picked up the kit a while ago, but it has just been sitting on my desk waiting for me to be inspired enough to install it. I finally got off my ass today, and it was one of the easiest installs I've ever done. Everything fit perfectly, without any drama getting the bushings to align. I think total install time was maybe 30 mins, garage door open to closed. I knew upgrading these bushings had made a massive difference in my old WRX, but I assumed the STi would have had stiffer bushings from the factory, thus I should perceive less improvement. As Social Distortion once sang, I was wrong. I love my Nameless Performance exhaust, but this was probably the most beneficial upgrade I've done to the car to date. I've noticed zero increase in NVH, but so much on/off throttle slop is gone. The drivetrain is almost as responsive now as when I had Cusco motor and trans mounts, and aluminum diff mounts on my old car, without all the effort that setup entailed. Deeeeeee-ecent!!!