should i put a cold air intake on my 280zx n/a i wonder if it will give me anymore horsepower. i also have headers and pretty much a straight pipe

The stock set up is already a "cold air intake". I don't think you'd see any noticeable improvement from adding one. Though you'd drop some front end weight by getting rid of the stock air box and it'd look way better too. It's really easy to make your own out of a piece of mandrel bent aluminized exhuast tube and a K&N filter to fit on the end. You might get slightly better air flow and more noticeable intake noise when you step on it with this set up.
It may be worth it just for the weight savings and looks alone!

id do it helps engine breathe better plus i like the sucking noise lol makes it growl :) well i am gonna do it...plus it just looks better than that crappy ass blue container

I still got the crappy ass light blue container, but i stuck a K&N filter in, but not the full K&N filter charger, it was like 60 bucks more for the full deal but the full intake will flow a bit more. Basically since you have the headers and the free flowing straight pipe, you will notice much more of a difference than with the stock exhaust. It may not give you magical hp gains but it will probably give you a few and help balance out the exhaust.

it sounds like a good idea but do they even make kits for that or would it have to be made custom

You can make your own and get a K&N and as long as you keep it in front of the radiator, which is where it belongs, your noise level won't increase, for you. For bystanders it will.,