The D while in the engine code means dual overhead camshaft (DOHC). This is often achieved by fitting an RB25DE or RB26DETT cylinder head and or turbo to an ordinary RB30E/T block. The RB25DET is just not ordinarily used. Keep that in mind before beginning on your RB25 Develop, as https://motor-rb2671820.is-blog.com/34511645/what-does-motor-rb26-mean