Here's Roush's Hellcat-Bothering 800bhp+ 2015 Mustang GT Screaming On The Dyno

Modifications, according to the YouTube description:

Stock engine and our phase 1 Supercharger kit hardware plus the following upgrades: 75mm supercharger pulley, upgraded fuel injectors, revised version of our 2011-2014 fuel pump booster kit, and minor calibration enhancements. Testing was done using 93 octane, stock manifolds, and stock catalytic converters. As you can see, with some small modification to our PHASE 1 hardware, our 2.3L supercharger kit is MORE THAN capable of making in excess of 800 horsepower at the crank.