We may be buying a 2014 GT next week and wanted to make sure that 91 octane would work without 'pinging' issues. We live where 93 is available so no problem but we travel a lot and we see 91 as the top octane, especially out west. Our current '07 GT of course takes anything so we would just like to confirm. Thanks!

 

91 should be fine, assuming it is running the factory tune. It can use any octane 87-93 and will automatically adjust. It is the same as your '07, except it will adjust to take advantage of the higher octane, which the '07 did not do.

However if it has an aftermarket tune that is written for 93, that might kill that self-adjusting feature and require 93 all the time, I am not sure

 

My ‘13 5.0 with ProCharger runs fine on 91.

 

If the "14" GT is running on the stock calibration tune, then yes, it will run just fine on 91 octane fuel...

 

I just read my owner's manual last night and I am rather stunned that you can use 87, just like you said. There was a mention afterwards which also confirmed what you said about the performance being enhanced by using higher octane. Thanks Bert!
Since I drive so little I'll probably use the 93, but it's good to know on the long highway trips we take, we can put in a few tanks of 87 just for cruising the highway. Ford gets a pat on the back for this one.

 

The 2014 GT is rated at 420HP on 93 octane and I believe it is 410 on 87 Octane.

 

IIRC If there's an aftermarket tune written for 93 octane fuel, the vehicle will also require it as well.. Aftermarket tunes are not capable of automatically making adjustments for switching to lower octane levels as the factory tunes are...