Air born
Racecar Engineering|December 2021
Every racecar engineer's dream is a blank sheet of paper design. When Hoonigan and Subaru approached Vermont Sportscars about building the next generation of Gymkhana racer, that's just what the company was given
LAWRENCE BUTCHER

Racecars are defined by regulations. From the entry-level kart to F1, the rulebook dictates what can and can't be done, rather than what an engineer may think is the ideal approach. The skill in designing and building a winning racecar is finding every ounce of performance within the rules, but not breaking them.

Throw that rulebook in the bin, though, and things get a whole lot more fun. The result? Cars like this, built by Subaru's works team in the US, Vermont Sportscars (VSC).

The company has a long history of constructing cars to the 'rules, fielding a variety of machines in Rally and Rallycross, but this project was very different.

Initially built for the Gymkhana video franchise (for those not familiar, these were essentially a showcase for driver, Ken Block, sliding around like the 'Hoonigan'he is in various high-profile locations), the franchise is now known as Airslayer, and encompasses more than just videos, while former FMX star, Travis Pastrana, has taken over as wheel man.

Setting the stage

The VT20G is based on a 2020 Subaru WRX STi that VSC uses for its Rally and Rallycross programmes.'Given the initial request from Hoonigan (Block's brand) and Subaru, it was obvious to start from a Rallycross car/explains technical director, Bertrand Vallat, who was chief designer at Hyundai Motorsport prior to his move to Vermont in 2019.'What they wanted from the car in terms of jumping, power, sliding and driveability was very similar to the requirements for Rallycross! However, while this car is similar to a Rallycross version in its underpinnings, it moves the performance to another level. Its turbocharged boxer four engine displaces 2.3-litres (compared to 2.0-litres in RX) and puts out over 850bhp, 200bhp more than even the most potent RX machines.

Likewise, the aero package goes far beyond that allowed in Rallycross, not least thanks to the addition of a driver-adjustable rear wing. More on that later.

The car started life as a body in white Subaru WRX, the majority of which was then either removed or modified in one form or another. Underneath, the transmission tunnel was opened up to accept the Sadev-supplied, six-speed transmission, from the same family as the company's Rallycross unit, but heavier duty thanks to the use of 24mm rather than 20mm gears to withstand the power hike.

'It was a compromise on weight, because when you have a wider gear, you have a bigger gearbox, which means you have a heavier gearbox in the end, admits Vallat.

The upgrade was considered necessary, though, and did not unduly compromise the overall car package.

Mounting positions

The engine sits approximately 200mm further back in the chassis than the production car, which in turn means the transmission is almost centrally mounted, using a torque tube connection from the engine and prop shafts driving the front and rear differentials. With the engine mounted so far back in the chassis, the front differential, produced by VSC (the rear is Sadev unit), actually sits under the engine block in order to place the driveshafts in the correct location relative to the hubs.

Steering is provided via a hydraulically assisted rack with an 11:1 ratio, and notably, the wheelbase is close to stock, a hangover from the Rallycross base design.

Though not built to any particular rulebook, the bodyshell was outfitted with a full FIA-compliant roll cage, braced into the front and rear shock towers. All trace of the factory subframes was removed, with bespoke units fabricated from tubular steel to support the MacPherson struts front and rear. The suspension gives all the adjustment one would expect in terms of camber, caster etc, as do the Reiger dampers.

The suspension is the one area of the car that is closest to being built to a regulation set, as many of VSC's existing Rallycross components were used.

Continue reading your story on the app

Continue reading your story in the magazine

MORE STORIES FROM RACECAR ENGINEERINGView All

Talk the torque

More thoughts on in-wheel motors and their effects on twisting force

6 mins read
Racecar Engineering
December 2021

Rolling about

An explanation of the limitations of a previous load transfer article, bringing jacking forces into the mix

5 mins read
Racecar Engineering
December 2021

F1 breaks schedule records

The FIA has confirmed no fewer than 23 races on the 2022 Formula 1 World Championship schedule, the highest number of grands prix ever to be held in a single season, and that has led to criticism from some teams that will be on the road for eight months.

1 min read
Racecar Engineering
December 2021

Under pressure

Toyota may have finished first and second at Le Mans this year, but the effort required to overcome a fuel delivery problem and finish with both cars was Herculean

10+ mins read
Racecar Engineering
December 2021

Physics at work

Dutch company, Intrax, offers Racecar Engineering an insight into the technologies it employs to optimise its suspension products

4 mins read
Racecar Engineering
December 2021

Williams' 2030 ambition

Williams Racing has committed to becoming climate positive by 2030 as part of an all-new sustainability strategy.

1 min read
Racecar Engineering
December 2021

Diff'rent strokes

Racecar looks at the different types of mechanical differential, their benefits and limitations

10+ mins read
Racecar Engineering
December 2021

Das Boot

A curious Twitter exchange fired up a unique, hydrogen-powered, cross-country project that will contest the Baja 1000 in November 2022

8 mins read
Racecar Engineering
December 2021

Air born

Every racecar engineer's dream is a blank sheet of paper design. When Hoonigan and Subaru approached Vermont Sportscars about building the next generation of Gymkhana racer, that's just what the company was given

8 mins read
Racecar Engineering
December 2021

Remote control

Called variously ‘virtual garages’, ‘mission control’ or ‘race support rooms’ is the future of race engineering sitting in the warm back at HQ?

10+ mins read
Racecar Engineering
December 2021