To satisfy his doubts, Rybeck first tested both body types in Volvo's own wind tunnel in Gothenberg. The results showed that there was little difference between the two body shapes, and in fact the estate offered better downforce over the saloon due to it's long flat roof.

Rybeck also brought in motorsport experts Tom Walkinshaw Racing (TWR) to evaluate the estate as a potential racer. TWR, who had been Volvo's on track rival when it raced in the European championship during the 80s, confirmed that so long as the weight could be brought down to the legal minimum, there was unlikely to be much difference between the two cars on the circuit.

Volvo confirmed its intent to join BTCC towards the end of 1993, and showed both saloon and estate racers at the Swedish Motor Show the following January. This generated enormous media speculation until Volvo finally came clean and announced at the Geneva Motorshow a month or so later that they would actually be racing the estate. Although the decision to run the estate was taken quite early on, the go ahead to build the race cars was not given till extremely late in 1993. The 3 year contract to run the cars was given to TWR, who struggled to get them ready for the first race of the season. In fact the first full race car did not turn a wheel until the first test session at Snetterton on the 4th April, a mere seven days before the first race of the season.

Unlike the red test car, the race cars were designed by TWR at their Oxfordshire base, the original design work performed by Richard Owen, the same man who penned the Jaguar XJ220 for TWR back in late 80s.

Although new to Super Touring racing, TWR has a vast experience in touring car racing and other forms of motorsport and they used much of this knowledge when designing the 850 in an attempt to make the car competitive.