Top Gear's guide to the Audi 90 Quattro IMSA GTO

Audi enlisted Bob Tullius’s Group 44 set-up to manage the squad – Tullius had raced British Leyland cars including the E-type and Triumph TR7 a decade before, with startling and some would say improbable success – and Hurley Haywood, Walter Rohrl, and Hans-Joachim Stuck were enlisted to race them. A formidable line-up. Audi won the championship, taking eight wins out of 13 races, partly down to a 2.1-litre engine that they somehow squeezed 510bhp out of, but much more due to the indomitability of the Quattro powertrain, with a Torsen differential and limited slip diff operating on the front and rear. So much so, in fact, that all-wheel drive was banned by those pesky Yanks at the end of the season.