i bumped mine to 14 and it ran like poo untill i ran the supreme 94 . :tup

The "rule of thumb" in regards to this is if you are running 14 degrees or more of base timing you SHOULD be running 91+ octane fuel TO BE SAFE. That being said, there are lots of people, some of who have chimed in in this thread that have run 14 degrees on regular fuel without audible pinging. Its simply a guideline. Personally, I run 15 degrees base and Ultra94 in mine, why? For peace of mind, I know its not going to ping no matter how hard I drive it.

Really, the decision is up to you. You are running 12 degrees base, you'll be just hunkey dorey with 87 octane.

I drive a 94 GT Bone Stock as of right now and near the end of last summer I tried the "low grade" petrol and within 4 to 5 weeks developed an engine knock. I could hear it and feel it when I would let her eat. Scared the hell out of me. Went back to "High test" and it cleared up within 7 to 10 days. Plus better power,perfomance, gas millage and peace of mind all for a few extra dollars. Plus I try to stay away from the small Mom Pop Convience Store gas and go's. Ya get what ya pay for and this is my car.

If your timing has been bumped up (previous owner perhaps?) Your engine had the potential to ping under load using regular gas, which is probably what you experienced.

i've got my timing set at 14 deg, and i run 94 octane...works great..just a personal preferance i guess...

Every car is a little different. After doing a lot of experimenting I've found my car runs best at 15* with 93 octane. Since it's so hard to find that around windsor I just use 94. It'll be what I have to use after next weekend anyway.

Gas Grade
 

I always use Sunoco Ultra 94 in my car. Nothing less than that!!