The 2.5 L RB25 engine was produced in four forms:
- RB25DE - NON-TURBO twin-cam 140 kW/190 PS (180 - 200hp ) @ 6000 rpm, 255 N·m (26.0 kgf·m) @ 4000 rpm)
- RB25DET - twin-cam TURBO (T3 Turbo) (245 to 250 hp and 319 N·m)
- NEO RB25DE- NON-TURBO twin-cam 147 kW/200 PS @ 6000 rpm, 255 N·m (26.0 kgf·m) @ 4000 rpm)
- NEO RB25DET - twin-cam TURBO (206 kW (280 PS) @ 6400 rpm, 362 N·m (37.0 kgf·m) @ 3200 rpm)
RB25DE and DET 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, both the RB25DE and RB25DET had a revised electrical system and the turbo charger on the RB25DET had a plastic compressor wheel rather than aluminium. Generally these engines are referred to as Series 2 engines. 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 exactly the same.
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 and a revised inlet manifold, in particular the RB25DE NEO which had 2 inlets going into the inlet manifold. The combustion chamber of the head is smaller, so GT-R spec connecting rods are used to compensate. The turbo received the larger OP6 turbine.
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 WC34 Stagea. Early R34 Skylines use the non NEO RB, later models use the NEO version.
R32 Skyline RB25DE Camshaft duration 240°in, 232°ex lift: 7.8mm in, 7.3mm ex
R33 Skyline RB25DE Camshaft duration 240°in, 240°ex lift: 7.8mm in, 7.8mm ex
RB25DET Camshaft duration 240°in, 240°ex lift: 7.8mm in, 7.8mm ex
RB25DE NEO Camshaft duration 236°in, 232°ex lift: 8.4mm in, 6.9mm ex
RB25DET NEO Camshaft duration 236°in, 232°ex lift: 8.4mm in, 8.7mm ex