text: In May 1998 a NEO head was fitted, which enabled the engine to be classified as a low emission vehicle (LEV) engine due to their lower fuel consumption and emission output. The NEO head featured solid lifters rather than hydraulic, revised camshafts, with on/off solenoid Variable VCT, used a hotter  thermostat, model-specific coil packs and a revised inlet manifold (the runner diameter is reduced from  to increase air velocity and low end torque) in particular the RB25DE NEO which had two inlets going into the inlet manifold. The combustion chamber of the head is smaller so model-specific pistons are used to compensate. The turbo received the larger OP6 turbine wheel, while some came with an aluminium compressor and super alloy turbine wheels, others had the nylon plastic compressor wheel and ceramic turbine wheel. Turbo engines were upgraded to use GT-R spec connecting rods. Some also used an N1 type oil pump and had the oil pump drive collar on the crank revised to help cope with the breakage problems associated with fast, high revs.
  All in all they are quite a different engine in their own right - a culmination of 20 years of Nissan RB engine building rolled into one.
  The non-VCT, non-turbo RB25DE was fitted to the R32 Skyline, the VCT turbo and non-turbo was fitted to R33 Skylines and the WNC34 Stagea and the Laurel C34. R34 Skyline, C35 Laurel and later Stagea (WGNC34) models use the NEO RB.
  The 2.5 L RB25 engine was produced in four different forms:
  RB25DE
  twin-cam, non-turbo with 10:1 compression ratio
  Power:  at 6000 rpm
  Torque:  at 4000 rpm
  RB25DET
  twin-cam, turbocharged (T3 Turbo) with 9:1 compression ratio
  Power:
  Torque:
  RB25DE NEO
  twin-cam, non-turbo with 10:1 compression ratio
  Power:  at 6000 rpm
  Torque:  at 4000 rpm
  RB25DET NEO
  twin-cam, turbocharged (T3 Turbo, "45V3" with OP-6 Compressor) with 9:1 compression ratio
  Power:  at 6400 rpm
  Torque:  at 3200 rpm)
  RB26 (2.6L I6)