im asking this becasue i am removing the emissions along with the omp and air pump and i just want to wire my 5th and 6th ports open... now i know that lots wont agree with just wiring them open but i personally dont care if they operate as i will lose what maybey 5hp below 4k? its a sacrafice im willing to make. ( i might even just remove them all together).

but onto my question what is the function of the vdi and do i really need it>? because i would prefer not to hook it up if possible.as i wont have any air pump

 

You don't NEED the VDI, but if you take it off you are losing 15+ HP. I guess you would just wire it open, but that will KILL low end power, I would estimate at least 25-30 HP. But since you apparently don't care about power below 5k, that is your best bet.

 

You'll loose more power from disabling the 5/6 ports and VDI than removing the air pump will give you back. Leave it on, it's not much of a drag.

 

k scratch that i guess ill leave the airpump on then i didnt know it was 25 to 30 hp

 

Its not that much of a drop from just the aux ports, but the VDI wired open also saps power.
After thinking about it its not probably 25-30 hp, I was basing that on the percentage of max power. Its still a noticeable drop, and the car feels quite sluggish below 4-5k.
On an S5 there is no real reason to remove the air pump. I would be surprised if it causes more than a 1-2 hp loss in power since all its moving is air. You already have a very efficient, reliable way of operating the aux ports and VDI, don't get rid of it.

 

i was just tryoing to clean up the engine bay i hate vac lines and such. but ill keep it

 

I agree, it does clean up the engine bay, but there aren't too many vac lines associated with the aux and vdi systems. I'm not super familiar with them (I have an s4) but you should at least be able to simplify them to some extent if you wish.