Gibson, not to disagree with the Speedchannel, but I've got 4 years experience that says the low grade doesn't make much if any difference in a high compression engine. Admittedly, my engine isn't quite the thoroughbred that a 911 engine is (although it is only about $2500 away from being able to put out the same HP as a stock 911 Carerra), but has almost the same compression (mine is 9.5:1, a Turbo S is 9.4:1) I've got a turbo 1.8T VW engine, that requires 91 minimum, and decided to try 89 some time back. I've never seen a reduction in performance, or mileage. When I take long trips, I used to normally run 91 or higher, and got 31.5mpg cruising steady on the highway, and 24.5 around town. Later after switching to 89, the mileage stayed the same, 31-32mpg. Acceleration (admittedly seat-of-the-pants) does not feel any different.
