So the dealer says use 93, would it be ok to use lower, what would be the huge difference?

 

The dealer told you use 93 octane? I am sure 91 octane is the recommended fuel for the G's. You're also able to use lower grade fuel, but the performance will slightly decrease.

 

100 octane race fuel, obviously

 

Read the manual. 87 is fine. The only difference is that you lose some performance, and maybe a little less MPG. Otherwise, no harm to your engine done. Your computer system will automatically adjust timing of the burn.

Recommended is 93 for best performance.

Please read the manual before posting things that can be answered easily. I'm sure there are a lot of threads about this already on this forum.

 

Tons of threads on this already, seach.

Cliffs: 91+ is recommended for all G37s, cheap people use 87 but get slightly less performance.