text: This engine used carburetors instead of the Nissan ECCS fuel injection system. It is able to rev higher than the RB25DE/DET (as it has the same stroke as the RB20DE/DET) as well as being almost the same displacement as the RB25DE/DET. A common modification is to fit a twin cam head from other RB series motors while retaining the carburetor set-up. The standard single cam form produced  at 5,000 rpm and  of torque at 3,000 rpm.
  RB25 (2.5L I6)
  The RB25 series of engines was first introduced in the R32 Nissan Skyline GTS25 sedan and coupe models. RB25DE (Naturally Aspirated) and DET (Turbocharged) engines produced from August 1993 also featured NVCS (Nissan Variable Cam System) for the intake cam. This gave the new RB25DE more power and torque at lower rpm than the previous model. From 1995,(Series 2 Engines) both the RB25DE and RB25DET had a revised electrical system and the turbocharger on the RB25DET(S2) had a ceramic turbine
  wheel rather than aluminium. The most obvious change to the system was the introduction of ignition coils with built in ignitors, therefore the coil ignitor that was on previous models was not used. Other changes were, different air flow meter, engine ECU, cam angle sensor and throttle position sensor. Mechanically Series 1 and Series 2 are very similar, the only mechanical difference would be the camshafts as the Series 2 Cam Angle Sensor's shaft that goes into the exhaust cam is slightly different. Early Series 2 featured the traditional Mitsubishi CAS which was later swapped for the Black CAS because of a positioning tooth which occasionally broke off.