On my fuel tank it says "Premium Unleaded Only", does that mean I can use both premium and unleaded or I use the lower grade of premium?

 

Premium means 91 octane unleaded or better. Don't run anything less or you're engine won't run right.

 

so your saying i should run premium atleast 91 or better

 

100 octane...woohoo!

 

Exactly. running less than 91 causes detonation under load which will cause your ecu to retard timing and richen the ratio. The car will run like a fat pig. You will be boosting about only 7 psi max because the factory boost controler will be shut off ad you will only be using the wastegate on the turbo which opens at about 7 psi. It's not a good thing.