Fuel Question
 

Do you have to use Premium or can you use the middle 89 ?

The manual says you can use mid grade, you have a turbo I assume? The performance will be reduced, I'd be surprised if these cars didn't have computer controlled knock sensors and fuel sensors and compensated for it.

Yes I have a Turbo. I wonder if the performance by how much. Has anybody alternated between 91 & 89 ?

I would NOT use mid grade , the computer will dial back timing ect to prevent detonation and lose performance.
Not only that there is a GOOD chance that the motor will have troubles running the midgrade as there will be valve build up issues ...

My friend is a mini service manager , he states it this way , " You can pay an extra $1/$1.30 a tank full, Or you can pay me $2000/$2500 to redo the heads WHEN you have troubles."
Notice how he states WHEN you have troubles , not IF ...

You can always drop in some 44K fuel injection cleaner every 4 fill ups or so and solve the build up issues.

I'm sorry the cost of the fuel cleaner will likely equal the cost of just running premium

Mid grade is fine, even regular will work for reqular driving. The computor will adjust for pre ignition. If you drive fast with the AC on and loaded with passengers use 89.
You will most likey have to clean the intake valves at 60k either way. So use cheaper gas and save for valve cleaning. A problem on R56 Cooper S.

How much would the cleaning be though

What if u don't have a turbo? Would reg gas be fine or should i still use premium?

I thought midgrade was fine for the non turbo. Does it have variable timing? If all of the engines have variable timing then you can use any fuel grade you want. The fuel efficiency might be a little less.