The D from the engine code means dual overhead camshaft (DOHC). This is certainly attained by fitting an RB25DE or RB26DETT cylinder head and or turbo to a regular RB30E/T block. The RB25DET just isn't ordinarily used. In 1995, Nissan revamped the RB25 series and designed quite a few changes. https://buyrb26dettengine36109.verybigblog.com/27917348/rb26-engine-for-sale-an-overview