used a numerical system (e.g., 127, 128, 124, 131) denoting relative position in the model range, the X1/9 retained its prototype code as its marketing name. Fiat's prototype coding used X0 for engines, X1 for passenger vehicles and X2 for commercial vehicles. The X1/9 was thus the ninth passenger car developed using the nomenclature. Production and model evolution Originally slated to debut at the November 1972 Turin Motor Show, the X1/9's launch was delayed until after the show to avoid upstaging the new Fiat 126 city car. Press test drives were held at the end of November 1972, on the Sicilian Madonie roads home to the Targa Florio road race. The car was intended to replace the 850 Spider, another Bertone design, not the larger and pricier 124 Sport Spider whose production continued for much of the X1/9's life. The car's monocoque body was produced at the Bertone factory in Grugliasco (Turin) and then transported to the Fiat's Lingotto factory for final assembly. As mentioned before, the X1/9's type 128 AS single overhead cam inline-four engine was derived from the Fiat 128, specifically from the 128 Coupé 1300. Changes included a new cast aluminium oil sump, complementing the aluminium cylinder head. With a twin-choke Weber 32 DMTR carburettor and an 8.9:1 compression ratio, the engine produced at 6,000 rpm and of torque at 3,400 rpm. The all-synchronized 4-speed transmission was also carried over from the 128, though with a taller fourth gear ratio to exploit the sports car's better aerodynamics. As a consequence the X1/9 had a top speed of over , 10 km/h higher than the similarly engined but 65 kg lighter 128 Coupé 1300. As standard the X1/9 came with 4.5J×13-inch stamped steel wheels fitted with tyres, while cast alloy wheels were an extra-cost option. Suspension was fully independent, with MacPherson struts front and rear. The split circuit brake system used equally sized solid discs all around. Steering was rack and pinion. The interior, upholstered in leatherette, featured two bucket seats with integrated headrests and a four-spoke steering wheel (resembling the one fitted to the Lamborghini Marzal). The engine cover and rear trunk could be opened with (lockable) interior latches located on the driver's side door jamb. The original 1.3-litre, 4-speed X1/9 can be distinguished from the later 1.5-litre, 5-speed model by its wrap-around steel split bumpers with rubber blocks, and the shallower engine compartment lid. Fiat began