designation. A plaque inset in the glove box door designated the number of the car out of the series of 350 (XXX of 350). Later there was the GTV 6 2.5 Maratona, of which only 150 were built. The Maratona model included a more aggressive aerodynamic trim package, lightweight Speedline wheels, clear engine view port, sunroof, wood steering wheel and shift knob, rear louvers and Carello fog lamps. All 150 cars were available only painted silver and with a black leather interior; and came with "Maratona" badging on the rear decklid, front fenders and glove box door. (The most notable feature of the Maratona, its aerodynamic kit, was also available as a dealer-installed option on other GTV-6 models.) Callaway Cars, famous for their later Camaro, Impala SS and Corvette offerings modified between thirty and thirty-six (depending on whether one "counts" those cars with Callaway components which were not assembled by Callaway but, instead, had those components fitted by Alfa Romeo dealers) twin-turbocharged GTV-6s between 1983 and 1986. These are called the Callaway C3, as it was the company's third project. of which the first five (the cars produced between 1983 and 1985; these were sold and titled as 1985 model year cars, save for the first prototype which was sold and titled as a 1984) were prototypes. Callaway "production models" were otherwise listed as from the 1986 model year. In addition to numerous small component upgrades, the Callaway GTV 6's included a somewhat revised suspension (most notably eschewing the metric Michelin TRX wheel/tire combination—then standard on the GTV-6, in favor of Pirelli or Goodyear tires on conventionally sized BBS, Speedline or OZ lightweight alloys), improved brakes and, most importantly, a twin-turbocharger system, boosting performance to exotic levels. Power is at 5500 rpm; up by fifty per cent over the factory car. A different twin-turbo GTV was also built briefly for the Australian market. GT, GTV and GTV 6 racing versions by Autodelta Racing versions of the Alfetta GT and GTV were built by Autodelta, initially with the naturally aspirated engines from the earlier GTAm racer based on the 105 series coupé, for homologation under FIA Group 2. There were some variations ranging from the Alfetta GT 1800 cc engines with twin-plug or even 16-valve heads up to the powerful 2-litre GTAm engine. In this form they were rallied with moderate success in 1975, winning the Elba and Costa Brava rallies