Keith Murray’s oddball Audi might have some scratching their heads, but in opting for a 2.0-liter TFSI motor over the standard V10 (or V8), he trimmed lots of weight, improved the weight distribution, and laid the foundation for one of the more intriguing cars to hit the hillclimb scene. Plus, with 650 horsepower, it’s not exactly lacking in grunt.

The motor is a combination of the TFSi 2.0-liter ALT 20v aluminum block with a 16v ABF head from a Mk3 Golf. Some might cock an eyebrow at the inclusion of an old Golf head in such a no-compromise build, but this head is more easily converted to solid camshaft lifters, despite the 20v breathing better. Mated to a remarkably responsive Garret HTA turbo, it can produce 650 horsepower and over 420 lb-ft of torque at 2.1 bars of boost. That thrust is sent to the rear via a triple-plate AP basket clutch, a steel Helix Autosport billet flywheel, and an Elite TXL 600 six-speed sequential gearbox to an Elite limited-slip differential.

This unique engine swap is undoubtedly the centerpiece of Murray’s build, but of course, it’s part of a larger package. The requisite rear subframe supports the motor, and, adhering to the rulebook’s points helps bring the total weight down to around 2,100 pounds. It also improves weight distribution; it now boasts a 45/55 weight ratio, as compared to the 30/70 ratio with the heavier V10. In fact, Murray is so concerned with weight he runs two different fuel tanks for different circumstances; a 10-liter tank for shorter races and a 45-liter tank for longer ones.

The weight is further reduced with a comprehensive carbon weight reduction program. The engine cover is carbon, and the rear window is polycarbonate. Polycarbonate side windows, carbon-kevlar front and rear bumpers, and a carbon rear wing all help trim heft. At the end of the day, the car changes direction in a way that doesn’t seem to fit. When the smaller motor provides the odd soundtrack, it takes a second to recognize that this is based on the plush, road-going supercar.

Murray paid homage to Audi’s racing history with the famous grey, black, and red color scheme.

Putting a smaller motor like this under serious stress works in short-race settings, though he’s gone to some lengths to protect his investment. A serious list of fueling modifications help the motor make that sort of power. Twin Bosch fuel pumps, a SEM rail, and 1,450cc Asnu injectors quench the ravenous four-banger’s thirst, and a Motec M800 ECU safeguards his custom motor and ensures every pony is safely squeezed out of the package.

The bodyshell is factory Audi, but most of the car — the front suspension, all the rear suspension, engine, running gear — is all custom. He’s integrated the Audi R8 LMS suspension, however. It is, truly, a silhouette car; with the carbon-steel rollcage extended out to stiffen the chassis and provide attachment points for the drivetrain and rear suspension. Fortunately, the classes it runs in — the Castle Combe Over Two-Liter Sports, GTs, Saloons, Touring Cars, and Silhouettes — allows for this level of modification.