For 1991, Nissan officially withdrew from the World Sportscar Championship. However Nismo planned to continue competition in the All Japan Sports Prototype Championship, and decided to upgrade the R90CPs to better compete with Toyota and Mazda. The new cars, known as R91CP and R91VP, would have slight modifications over the previous car. Most notably, the boxy turbo inlets which had been placed on the rear fenders of the R90CP were made into smaller slits, while a large snorkel was added to the top of the engine cover to cool the rear brakes, in place of the previous twin brake ducts. The cars would be further modified for 1992 with an upgraded VRH35Z twin-turbo V8, while the cars were renamed R92CP.

For the R90CKs, Nissan ran them mostly at the 24 Hours of Daytona following their retirement from the World Sportscar Championship at the end of 1990. For the 1992 running of Daytona, the R90CKs would have their VRH35Z engines replaced with smaller 3.0L twin-turbo V8s, although they would not be as successful as the race winning R91CP.

Three other unique R90Cs were cars that were based on existing cars but modified. One R89C was upgraded to become an R90CP, originally used by Nissan in the JSPC before all cars were completed. Nova Engineering purchased chassis #07 from Lola and initiated their own upgrades to the chassis, calling the car a R91CK. The final modified car was an R90CP bought by Team Le Mans and modified into what they termed the R91VP. Both cars featured minor aerodynamic differences from the other R90CKs and R90CPs.