I did a test on this, calculating the cost difference of the gas into the cost per mile driven and found that even paying 30 cents more for premium gas, the most cost effective tune is the performance tune with 93 octane. I don't remember the numbers or where I posted them, might have even been before I was a member here, but if a search doesn't yield them here, then it's on that other forum with the initials D and T...

 

Good to come across this thread. I've only got a couple fill ups with setting it to MXS and have not noticed any increase in MPG, only decrease in power.

If i'm at half tank right now, can i set it to 91 tune and fill up the rest with 93 ? or should i wait until it is almost empty before setting it to 91 tune on next fill up?

thanks,

-D

 

If you've at least got 91 in her now then it is safe to make the switch in tune.