Ringbrothers Spent 5,500 Hours Widening This 650-Horsepower Pontiac

More than 5,500 hours went into turning a 1965 Pontiac Tempest Convertible into Billie, a 650-horsepower custom designed to resemble a carefully evolved Pontiac GTO. Ringbrothers widened the body by five inches, installed a supercharged modern V8 and reworked nearly every major area of the car while retaining the proportions and factory lines associated with the 1965 GTO.

The scale of that work is easy to underestimate because the finished body is intended to look cohesive rather than radically altered. The front fenders were reshaped, the rocker panels were lengthened and the rear quarter panels were widened. Those changes had to transition cleanly into one another across a convertible body, where the absence of a fixed roof makes the car’s long horizontal lines especially prominent.

Jim Ring, a Ringbrothers co-founder, said the challenge was adding five inches of width without losing the proportions that make the 1965 GTO recognizable. He described extensive work to massage the factory lines and refine the transitions between panels, with much of the fabrication concealed beneath relatively subtle exterior changes. The intended effect was a wider Pontiac that looked as though it could have been designed that way from the outset.

Carbon fiber is integrated rather than exposed everywhere

Billie combines its classic muscle-car shape with carbon-fiber components in several structurally and aerodynamically useful locations. The enlarged-scoop hood, functional vents, front wheel tubs, lower front valance and rear diffuser are all made from the lightweight composite material.

That distribution shows how modern materials were incorporated without allowing their appearance to dominate the design. The hood and vents affect the upper body, while the valance and diffuser place newer aerodynamic forms low on the car. Carbon-fiber wheel tubs help accommodate the widened body and wheel package in an area largely hidden from view.

Other fabricated details include custom bumpers, redesigned headlight surrounds and a one-piece aluminum taillight panel. The body is finished in a custom color called Billie Goat Blue, accompanied by polished chrome accents and black detailing. Together, those features preserve familiar Pontiac visual cues even though the panels surrounding them have been extensively changed.

A modern powertrain sits beneath the 1965 shape

Power comes from a Wegner Motorsports-supplied, supercharged 6.2-liter LT4 V8 producing 650 horsepower and 650 pound-feet of torque. Those figures match the specifications listed for the Chevrolet Performance LT4, which uses an aluminum block and forced induction to deliver modern output from a compact V8 package.

Ringbrothers paired the engine with a Bowler Performance 10-speed automatic transmission and a custom exhaust incorporating Flowmaster components. A Fast Track Stage III chassis provides the foundation, supported by Fox RS SV coilovers. Brembo brakes with six-piston calipers at both ends address the stopping demands created by the power and contemporary tire package.

Staggered HRE G-code wheels measure 19 inches at the front and 20 inches at the rear. They carry Michelin Pilot Sport Cup 2 tires. The combination places modern wheel, brake and suspension hardware under a body whose recognizable identity still depends on its 1960s surfacing and proportions.

The cabin required its own dimensional changes

The dashboard was moved four inches forward and two inches lower, a substantial repositioning rather than a simple instrument replacement. Custom aluminum trim and Dakota Digital instruments modernize the controls, while Vintage Air climate equipment and an auto-dimming rearview mirror add contemporary convenience.

One of the more restrained updates is the restored factory radio, which now incorporates Bluetooth connectivity. It follows the same approach used outside: preserve a period-appropriate visual element while changing the hardware behind it. A dashboard plaque reading “Raised by Ringbrothers” is a more explicit acknowledgment that this is a custom interpretation, not a factory GTO.

Presented in connection with SEMA in Las Vegas, Billie demonstrates where those 5,500-plus hours were spent: not only on installing a 650-horsepower engine, but on making a five-inch-wider Tempest Convertible continue to read immediately as a 1965 Pontiac.

By Robert McKinney — Editor-in-Chief for AMI’s automotive and mobility coverage, with a mechanical engineering background and a decade reporting on powertrain systems, EV innovation, and global vehicle manufacturing.