Originally Posted by Lug

400 out of a 3.8 of a general assembly line with turbos lets you dumb down the built, parts cost, complexity and lets you build a motor far enough away from it's fail point to make it reliable enough for mass production a car. Pushing more out of a 3.0 liter will make it less reliable. The 3.8 is block already developed and you won't need things like the spray in sleeves and full forged components that cost more. The GT-R's motor's cost comes from expensive parts, required tighter tolerances and hand-building, things you can dumb down at lower power levels. Nissan saves costs on uitlizing a block design that's already been in use and tested beyond anything they will need.