VQ35DE differences

What are the differences between the VQs that go into the Z, G35, Max and so on? If the answer is internals or tuning, what internals are different? What is tuned differently, timing? Is it the same for Toyota's precious 2JZ in the Supra, IS300 & SC300?

Actually i want to know tha same thing because i am about to buy an 2001 maxima with the vq and noticed the 350z has 300hp while the maxima has like 255, is it tuning or internals?