The steel Italian cars differed from the original AMC design in having fewer but functional rear decklid louvers, louvered hoods, and, in some cases, hood scoops to direct fresh air into the heating-A/C system. Further engineering improvements and road testing was done by BMW, which declared the AMX/3's chassis one of the stiffest having a 50% higher stiffness compared to a benchmark Mercedes-Benz model.[107] The car's steel semi-monocoque chassis design with its welded on steel body provided a strong overall structure while the top speed was verified to 160 mph (257 km/h), with reports indicating the AMX/3 could go faster if it was not for the tendency for the front end to lift at those speeds, but BMW found the car to be most neutral handling they had ever tested.[108] The BMW engineers also refined numerous components of the AMX/3 into "a world-class contender among the mid-engined super car elite of its time."[107] One of the cars became known as the "Monza" after it achieved a top speed of 170 mph (274 km/h) in testing at the famed Italian race track."[109]