Well here's my experience (I live in CA where we only have 91..). I tried 87 when I first got my car and used it for a few tanks and then I put in 91 and I got 40 miles per tank more on average. To me the car ran smoother and I noticed a tad more power. I use Shell and my car really seems to run much better than on any other gas. So for me, just the extra 40 miles per tank has me using 91 because the extra money spent for the higher grade of gas is more than saved with the extra mpg that I get. (Now I have an X3 with the 91+ tune so I have to use 91 unless I flash back to stock.)

So what I would do it calculate your average mpg that you're currently getting on 93 and then drive a few tanks on 87 and see your mpg and any drivability differences and make your decision from there. If there's no difference, then go with the 87 to save the .20 a gallon.

-Blk N Wht GT

 

Please stop wastin your $