All RB engines have belt-driven cams and a cast-iron block. Most turbo models have an inter-cooled 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.