You may know the Wantel S5 by "Was ist das?"
If not, download it here first: https://www.beamng.com/resources/wantel-s5.7643/ (of course I asked for his permission before uploading)
The Wantel S5 K-Performance is based on the V8 S with a 4.2l V8 BiTurbo with 545hp
K-Performance increased the displacemnent to 4845ccm, installed a race intake, just more of everything turbo-related, increased the rev-range by 1500rmp, installed a much sportier (and louder) exhaust etc to give the engine 1180NM torque at 3500rpm as well as 842hp. The transmission was swapped out for a Koyote Dualclutch gearbox.
The car got a weight reduction to 1676kg (if i remember correctly), got a stiffer suspension, race brakes, semislick tires, wider tires (and fenders), spoilers/wings to keep it on the ground etc. The esc was completely removed, as we figured out that every owner would disable it anyways so we could save weight.
Disclaimer: It is not made for the track. Of course you can drive there, but it still is a fairly big sedan. The car will understeer quite a lot at first glance, but if you drove 1-2 laps, the front tires will be warm enough to create the needed grip to not understeer.