JimD Before I got the Turner tune for my car, I ran 87 with absolutely no issues. Saved a few bucks per tank, and never noticed much difference (power, economy, etc). It did seem to idle a little less "securely" with 87 vs 93, but I don't like to spend much time idling anyway, so it wasn't a bother
. Before a track weekend, I'd just pump in some 93, and all would be fine. I now always run 93 because it's what is "required" by the tune (or 91). Maybe I'll try an eighth of a tank of 87 or something to see if it doesn't throw a fit, but not until winter time (or probably ever)...
BTW, I NEVER fill up at Shell, they are WAY overpriced and (IMO) they are full of themselves. Costco is my go-to, but I don't worry too much about where I stop, in a pinch. My intake ports are CLEAN, like eat-your-dinner-in-them clean (I wouldn't, for obvious reasons though) and the car has 176k miles (159k with another owner), and the engine is just a champ.
Our engines (even tuned) aren't very stressed, don't have very high compression, and just aren't going to see as big a difference with a higher octane gas as the turbo 1'ers will (E85 blends and whatnot).