Nothing is sacred in today's age, not even a limited edition $161,972 BMW M4 GTS. The M4 is already a great car, but the GTS swings the needle that rests right in between "road car" and "track car" on the M4 closer to the latter of the two options in the GTS. This means that the exhaust gets a proper yowl, the engine gets a power boost, and the chassis, styling, and aerodynamic elements get cranked up to 11. The result is a Nurburgring time on par with many supercars. Impressive as the GTS is, the kit isn't enough for BMW tuner G-Power.

Famous for taking powerful M3s and M5s and supercharging them to unleash silly horsepower numbers that turn the cars into proper sleepers, the tuning house decided to visit the rare GTS to give it a power treatment. Instead of adding a supercharger to an engine that already has air shoved down its throat via two turbochargers, G-Power decided to give the water-cooled six-cylinder some new internals. The aftermarket kit gives the GTS turbochargers new turbine wheels and housings, a free-flowing catalyst-less exhaust, and an ECU tune to let engine management deal with the new hardware. The result is that the G-Power team managed to up the GTS's horsepower rating from 500 to 615 horsepower.

Torque is up too, going from 442 lb-ft to 560 lb-ft of twist. Add these together and remove BMW's stock limiter and the G-Power M4 GTS now hurries from 0-60 mph in only 3.6-seconds and only relents change in forward inertia at 200 mph. Visually, things stay the same save for the 21-inch lightweight forged rims. Given that the M4 GTS is a rare bird that will become a collector's item in the near future, not all owners are going to want to mess with the engine on a BMW bearing the 1 in 700 status. This becomes especially important when considering that the tune boosts the engine to a risky 205 horsepower per-liter. For this conservative crowd, G-Power offers an ECU tune that offers 575 horsepower and 545 lb-ft of torque as a middle ground.