Going from a 92mm to 90mm will I need to retune
 

I am hoping not. I do have a WB I can monitor and HP Tuners for both cars so I can certainly make some small tweaks if needed. I was hoping however I could just swap pulleys and be good to go. I guess I should just log and see what happens.

Teddy you meant 95 correct? It will probably need just a little tweaking.

You are correct. I believe the car currently has a 95mm pulley on it, I just got my 90mm in the mail. I am guessing that is a bigger discrepancy and a retune is likely. Damn it.

if its by default and from the stock, you probably have the 98mm pulley. I went from 98 to 95, had to re-tune (just because I'm anal). but if your going by that much, then I'd say for sure, get it re-tuned. are you still on the canned tune?

Teddy skipped the 98mm and went to the 95mm and that's how it was tuned. It probably won't need a lot of change but you should call your tuner and see if he could do that for free since you just spent a shit load on the last tuning on the dyno.

agreed. if he already paid for the credits etc. it may not cost him that much then. when I had mine re-tuned (HP tuners) he only charged me 160 to re-strap it down and do 4 pulls/retune ect. hopefully his tuner is cool like that. either way, I'd re-tune it. he has alot of money involved anyway

Don't forget the belt. No way you will be able to use the same one when dropping 5mm

If you add more air then you have to add more fuel to make more power and keep the AFR in a safe range...so yes the fueling will need touched up.

^^what he said

get a datalog and send it to your tuner. Whenever you make a change to the amount of air going to your motor you should have your tune checked out.

I appreciate everyone's feedback here. Not sure what the tuner will want to do. He is about 2 hours away so just going down is not so easy. I might just hold on to the pulley until I am ready for drop in pistons or something. Being naive here I figured I could pulley down a bit and be fine would just need to watch up top. I honestly thought I was at 92mm so 90mm wasnt such a drastic change. Now it looks like I will need a new belt and tune. I should be happy with enough for now. I have not even put 250 miles on this car yet. LOL

So are we confident the K080850HD wont work or are we assuming. I was under the impression it would fit if I decided to use?

If your only dropping less then a 1/4" it should work.

Well we shall see. I am going to enjoy it for now. I need to leave well enough alone. I want to get scared I will jump in the C7. LOL