were introduced; although the concept's number (73) hinted at Nissan's racing efforts for 1973, Nissan dropped its factory team that year in favor of developing anti-pollution technology and improving fuel efficiency. Less than 200 examples of the KPGC110 GT-R would be built from January through April 1973, due to increasingly stringent emissions laws; in addition, the contemporary oil crisis of that year created a wasteful perception of auto racing and high-performance vehicles by many people. Because of its rarity and withdrawal from touring car races, the KPGC110 Skyline GT-R has been dubbed as the "Phantom GT-R". Engine specifications The S20 is an inline-six with a cast iron block and aluminum head, using a 7-bearing crankshaft. It features a dual overhead cam, cross-flow head with pent-roof combustion chamber and four valves per cylinder. Heads were ported and polished manually, and the motors were bench tested for consistent power production before installation. Compared to the preceding GR-8, the bore was retained but the stroke was reduced from in order to ensure that displacement would not exceed 2 litres if slight errors were made during manufacturing. In addition, the valvetrain was driven by timing chains, rather than gears. Most engines utilized triple Mikuni-Solex 40PHH dual-choke carburetors; models after 1969 offered optional Lucas mechanical fuel injection. In racing trim, the fuel-injected motors reportedly produced over , with for larger tracks like Fuji Speedway; custom tuning yielded race engines with output at 12,000 rpm. As fitted to Shinohara's No. 39 racing car (1969), the S20 was tuned for higher output, generating at 8000 rpm and at 6000 rpm. Applications This engine was used in the following vehicles: Skyline GT-R (PGC10 type) 4-door sedan 1969 - 1970. (832 units) Skyline GT-R (KPGC10 type) 2-door coupe 1970 - 1972. shorter wheelbase than the PGC10. (1,197 units) Skyline GT-R (KPGC110 type) January–April 1973. (197 units) Fairlady Z432 (PS30) 1969 - 1972. (419 – 420 units) Fairlady Z432R (PS30SB) Z432 race car-based for homologation nearly lighter than production Z432. (30 – 50 units) Motorsports The first win for the S20-powered Skyline 2000GT-R was on May 3, 1969, at the TS-b race of the 1969 JAF Grand Prix held at Fuji Speedway, using the four-door PGC10; the winning car (No. 39, driven by T.Shinohara) has been preserved in the Nissan Heritage Collection. The racing saloons were joined by the hardtop coupe KPGC10 in March 1971 at the All Japan Suzuka