I went to fill up my 2.5 gallon gas can for the weedeater with 91 octane. Instead of shutting off the pump and switching over to 87 for the car, I just left it on 91 and went ahead and filled up the car. Stihl recommends 91 or higher octane for their weedeaters. The engine feels like it has 50 more horsepower with the 91. How is that possible you say ? The only thing I can think of is that the knock sensor was retarding the timing with 87 the whole time and I never knew it. I mean it's not a night and day difference, but it's definitely noticeable. And besides that, fuel mileage is up 0.7 mpg. The engine is a 2000 Buick 3800 V6. Fuel is from Costco.