There are so many cars that I could talk about like this...
E30 M3 - Fully built track car
Built Low Compression motor, turbo, roll cage, ...
Oh wait, they already have one of those:
E30 M3 No front end
If it were to be on my car:
Built 2.0L bottom end, balanced, hot tanked, dry sump, the works
Fully worked heads, PnP, cammed, valves, springs, retainers, everything
GT3076R (screw twin scroll, I want a rumble) with anti-lag
Meth Injection, Nitrous
WRC Style mid-mount, reversed manifold Intercooler
PPG 1-4 straight, helical 5th, 4.44 final drive, custom ratios
2 way rear, DCCD center, helical front (Not sure if this is the best, need to read more about front diffs)
WRC Magnesium Wheels
Fully worked suspension
Group N spec cage
Basically a time attack car