I'm not sure how different this is compared to the 991. But let me tell you, I tried everything to get an decent sound out of that car. On the older models (997) it was easy, just deactivate the flap and the car was loud and angry. The new generation works different. It knows "different levels of open" - so just open it to the full, didn't make to much impact. Also ordered once a box with a remote control which promised to open it up, but it was total BS - didn't bring anything close to the 997 sound. I guess, if you want to do it right you need to invest into an decent sport exhaust and the car will start to sound like it should sound.