The RB engine is an oversquare 2.0–3.0 L straight-6 four-stroke gasoline engine from Nissan, produced from 1985 to 2004, and will be continuing production in 2019, after a 15 year hiatus. The RB followed the 1983 VG-series V6 engines to offer a full, modern range in both straight or vee layouts.

Both SOHC and DOHC versions have an aluminium head. The SOHC versions have 2 valves per cylinder and the DOHC versions have 4 valves per cylinder; each cam lobe moves only one valve. All RB engines have belt driven cams and a cast iron block. Most turbo models have an intercooled turbo (the exceptions being the single cam RB20ET & RB30ET engines), and most have a recirculating factory blow off valve (the exceptions being when fitted to Laurels and Cefiros) to reduce compressor surge when the throttle quickly closes. The Nissan RB Engine is derived from the six cylinder Nissan L20A engine which has the same bore and stroke as the RB20. All RB engines were made in Yokohama, Japan where the new VR38DETT is now made. Some RB engines were rebuilt by Nissan's NISMO division at the Omori Factory in Tokyo as well. All Z-Tune Skylines were rebuilt at the Omori Factory.
All Nissan engines follow a naming convention, identifying the engine family (in this case, RB), displacement, features present—see the list of Nissan engines for details.

The stock dimensions for the Nissan RB Engine

RB20 - 2.0 L (1,998 cc), bore x stroke: 78 mm × 69.7 mm (3.07 in × 2.74 in)
RB24 - 2.4 L (2,428 cc), bore x stroke: 86 mm × 69.7 mm (3.39 in × 2.74 in)
RB25 - 2.5 L (2,498 cc), bore x stroke: 86 mm × 71.7 mm (3.39 in × 2.82 in)
RB26 - 2.6 L (2,568 cc), bore x stroke: 86 mm × 73.7 mm (3.39 in × 2.90 in)
RB28 - 2.8 L (2,770 cc), bore x stroke: 87 mm × 77.7 mm (3.43 in × 3.06 in)
RB30 - 3.0 L (2,962 cc), bore x stroke: 86 mm × 85 mm (3.39 in × 3.35 in)
"D" indicates a dual overhead cam as opposed to a single overhead cam
"E" indicates the individual engine ports are electronically fuel-injected
"S" indicates the engine is carbureted
"T" indicates the engine has a factory installed turbocharger
"TT" indicates the engine has factory installed twin turbochargers
"P" indicates the engine runs on LPG (liquefied petroleum gas)