First modification was the exhaust.
Installed it a couple of months ago, after much research and many google & youtube searches...
I went with this one from X-FORCE https://xforce.com.au/products/subaru-levorg-gt-cat-back-exhaust
I'm happy with the sound. Not over the top loud at idle, no drone when cruising, and just the right noises when you drive more spiritedly.
Easy to install, just did it on the driveway with a mate.
