[1st K5]

I'm currently using shell 91, haven't noticed any difference in acceleration but I haven't gone over 4k rpm.
Manual says 87 or higher.

 

[Capsaintkiss]

87

 

[Stoberkins]

I am using Shell 87- they have some of the highest amounts of detergents in their gasoline and I want to keep the engine nice and clean on the inside. Plus, sign up for Shell Fuel Rewards and get 5¢+ off per gallon. If you have a Circle K/Shell station, get an Easy Pay card and it stacks on another 6¢ per gallon off. I have reached the 10¢ off fuel rewards tier and so I am saving 16¢ per gallon at the pump. If you get an Easy Rewards card, you save an additional 30¢ per gallon for the first 30 days that shows up when the card processes through the bank.. so right now for the next 30 days, I am saving 46¢ per gallon