The D inside the engine code means dual overhead camshaft (DOHC). This is completed by fitting an RB25DE or RB26DETT cylinder head and or turbo to a standard RB30E/T block. The RB25DET is not ordinarily used. This guideline is in this article to go over everything you need to know https://trevordqbcx.blogozz.com/27870202/not-known-details-about-nissan-skyline-rb26