Admittedly this is not a stock car, it can be seen at 1:29 in the video that it has a +50whp tune, giving 583whp, exactly the same as a stock 675LT.
http://www.fabspeed.com/mclaren-675lt-fabspeed-ecu-tune/
But surely the 675LT is 112kg lighter and has more downforce, and wider, stickier Trofeo R tyres. So how come such a simple mod makes it 2s faster than a 675LT? And only 1s slower with its amateur owner behind the wheel. Especially when it was 3s slower to begin with.
https://fastestlaps.com/comparisons/9a3p0m339pus
Porsche 918 Spyder James Sofronas 1:17.18 887 / 1640 Ferrari LaFerrari James Sofronas 1:18.46 963 / 1585 McLaren P1 James Sofronas 1:18.82 916 / 1490570S + 50whp Bryce Miller 1:20.91
Dodge Viper ACR (Mk V) James Sofronas 1:21.86 654 / 1548 Honda NSX (Mk II) Graham Rahal 1:21.90 581 / 1767 Dodge Viper ACR (Mk V) Alec Udell 1:21.92 654 / 1548 McLaren 675LT Alec Udell 1:22.62 675 / 1328 Porsche 911 GT3 RS (991) Alec Udell 1:22.64 500 / 1420 Veyron 16.4 Super Sport James Sofronas 1:23.01 1199 / 1888 SRT Viper TA Alex Gurney 1:23.40 649 / 1520 Aventador LP750-4 SV Alec Udell 1:23.56 750 / 1525 Pagani Huayra James Sofronas 1:23.76 730 / 1350