The D inside the engine code means dual overhead camshaft (DOHC). This can be attained by fitting an RB25DE or RB26DETT cylinder head and or turbo to a normal RB30E/T block. The RB25DET is not really ordinarily used.However, The 2 are rather similar, along with the RB25 is absolutely no slouch. You may consider the RB25 vs the RB26 as just like the