The S660 is a lightweight mid-engined roadster. Its dimensions, due to kei car size restrictions, are nearly identical to the 1990s Beat. It is sold with either a 6-speed manual transmission or a CVT with paddle shifters, both options being offered on the two trims available (Alpha and Beta). The S660 weighs approximately 830 kg with the manual transmission and 850 kg with the CVT, and is claimed to have a front/rear weight balance of 45/55.
The S660 is powered by the same turbocharged 658 cc S07A Turbo engine used in the N-One with some mechanical improvements. In the S660, this engine is mid-mounted and produces 47 kW (63 hp; 64 PS) at 6,000 rpm and 104 N⋅m (77 lbf⋅ft) of torque at 2,600 rpm with a redline of 7,700 rpm for the manual transmission and 7,000 rpm for the CVT. This gives the S660 a 0–97 km/h (0–60 mph) time of upwards of 10 seconds, with Car and Driver magazine estimating it to be between 13.2 and 13.6 seconds, and a top speed of 140 km/h (87 mph).