The D in the engine code means twin overhead camshaft (DOHC). This is often attained by fitting an RB25DE or RB26DETT cylinder head and or turbo to a standard RB30E/T block. The RB25DET isn't usually used. While this isn’t much an engine flaw around It is just a style flaw, https://nissan-skyline-rb26-engin26889.blogkoo.com/a-review-of-motor-rb26-47839504