The stock WRX exhaust has a decent sound, but the Invidia Gemini R400 Quad Tip exhaust is such an upgrade it almost feels criminal that it isn't the default exhaust. The R400 makes your WRX growl, accentuating the lower tones, while also filling out the engine's sound. The increase in volume helps you hear the engine more clearly, without being so loud it's annoying. I feel like that extra bit of insight I've gained from hearing the engine through the R400 has helped me refine the way I drive, particularly smoothness in lower gears. It's also very satisfying when you accelerate hard into higher RPMs, then get crackles and pops as the revs drop.