Originally Posted By: dparm
If anything, it may have hurt performance. I wouldn't run 93 unless the car specifically calls for it.
You cant lay that blanket statement out. While I agree, most cars that are designed to run on 87 will not gain much or anything, saying it will hurt the car is not true.
Originally Posted By: ahoier
I've heard running higher octane in an engine not spec'd for the higher test gasoline will result in un burned fuel causing carbon build up......
Which is why I think Shell adds the "extra" additive to their 93 AKI pumps
To help "break down" the possible carbon build up; and thus creates the age-old myth that higher octane = better clean
Higher Octane prevents preignition from compression. A spark plug will ignite 93 octane.
Shell adds extra additives because they are a part of the top tier fuel standards.
http://www.toptiergas.com/
Some cars that call for 87, like my car, can advance timing and use higher octane.
http://www.europeancarweb.com/tech/proven/epcp_1007_2010_volkwagen_jetta_proven/index.html