Click above for high-res gallery of the Pontiac G8 Street Concept

We couldn't help but listen to the comments of other onlookers as we closely inspected the G8 GXP Street Concept in the G8 booth. Every reaction was overwhelmingly positive, from the overall design to the motor. After all, what's not to like? For starters, the standard 6.2L V8 has been replaced with an LSX454 crate motor that uses the LSX Bowtie block, six-bolt LSX cylinder heads and a forged rotating assembly. In total, the 7.4L V8 pushes out a massive 638 horsepower and 600 lb-ft torque that's directed through a 6-speed automatic transmission. The exterior gets a makeover with new front and rear fascias, rocker panels, custom upper and lower grilles and black chrome trim. Inside, the G8 GXP Street Concept also gets custom leather trimmed seats, a new gauge cluster and more black chrome. Yeah, it's basically a four-door ZR1. You can look at all the details of the car in the gallery of live high-res photos below.

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G8 GXP Street concept

Both the Pontiac G8 GXP and the LSX454 crate engine from GM Performance Parts are new this fall. GM engineers figured there was no better way to highlight them than combining them in an intimidating street machine.

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 has a new, black-chrome, metallic look.

Overall, the G8 GXP Street concept can be summed up with one word: menacing. And with 638 horsepower on tap, it has got the muscle to back up the attitude.