The D from the engine code stands for twin overhead camshaft (DOHC). This can be accomplished by fitting an RB25DE or RB26DETT cylinder head and or turbo to a typical RB30E/T block. The RB25DET is not normally used. Brilliant folks about at jjsmotorsport. These guys went above and over and https://archermugpp.eedblog.com/28306339/5-simple-techniques-for-rb26-engine-for-sale