Are we talking in general about cars here or specifically about the Z? Wet Carbon Fiber or Dry? Manufacturing process? There are many variables before accurately providing a response.
Because if we are talking about the Z, you would know the Z comes with very light weight aluminum hood and fenders. The aluminum hood and fenders will weigh the same if not less than the CF counter parts. However this is entirely dependent on how the CF part is made. Some manufacturers wrap a fiberglass mold in Wet Carbon Fiber to minimize costs when fabricating. In other words, the piece is not entirely made of Carbon Fiber but only the top layer. This process does not result in weight savings and actually adds weight of the final product.
Dry Caron is a different manufacturing process and it will result in weight savings over the stock Z parts.
Now if you compare OTHER vehicles, you may see weight savings from all forms of CF parts over stock BUT when it comes to the Z, its not likely.
I also want to discuss how CF parts will react in case of an accident. Keep in mind, that stock aluminum hoods and fenders come designed with crumple zones. The material (aluminum) used will bend easily and not shatter into a million pieces upon impact. The Carbon Fiber hood will not bend and crumple as Nissan designed it which can result in serious injury and even death.
I would go as far as, in an event of an accident and you (the one with CF hoods and fenders, etc) are at fault, and your “aftermarket” parts caused unusual damage to my vehicle or myself, I would sue the crap out of you for reckless endangerment, along with any other possible crime I can sue you for.
