In factory form, the G8 GXP features a 6.2L (376-cu.-in.) V-8 rated at 415 horsepower (309 kW) and 415 lb.-ft. of torque (562 Nm), but the new LSX454 (part number 19166972) delivers 7.4 liters of unadulterated grunt. It cranks out 638 horsepower (476 kW) and 600 lb.-ft. of torque (813 Nm). The engine uses the LSX Bowtie cylinder block, new six-bolt LSX cylinder heads and an all-forged rotating assembly. Backing the LSX454 is the GXP's Hydra-Matic 6L80 six-speed automatic transmission.

Handling and stopping performance are enhanced with a lowered ride height, stiffer springs and a disc brake package borrowed from the Cadillac CTS-V. The calipers are painted red and feature CNC-milled GXP logos; they're visible through a set of customer 20-inch aluminum wheels with a sinister black chrome finish. They're mounted on performance rubber.

The exterior of the silver G8 GXP Street concept wears custom front and rear fascias and new rocker panels that give it a more aggressive appearance. The front fascia features unique upper and lower grilles, while the rear fascia incorporates a racing-style diffuser. All of the exterior bright trim has a black chrome finish. There's also a performance exhaust system with custom-cut aluminum tips exiting through the rear fascia.

Inside are custom, leather-trimmed seats with "GXP" embroidered on the headrests. There's also a new gauge cluster with unique graphics and the silver-finish factory trim