157dB

You have been wasting your $$.
No gains whatsoever running 93 Octane on a very pulled back for
long engine life Ford Stock tune.
You could run moonshine with Fords timing and fuel parameter tables with
no knock...
Just think, if you had the extra $$ you have been spending
on the extra un-needed Octane, you might have enough for a
CAI and a 93 Octaine tune....

Stock tune wont allow pinging on 87 Octane fuel.
It has knock sensors and pulls the timing to prevent this.

Goldenpony

Running 93 octane without a tune will not hurt anything, as a matter of fact, it might run just a bit better. I used to run 93 octane before I got my Brenspeed 93 octane tune and the engine seemed a bit quieter and idled smoother. Now, with the 93 octane Brenspeed tune, it runs noticably better. I went back to the 87 octane Brenspeed tune (along with 87 octane in the tank) for the winter and I could tell the difference. I'm back to 93 in the tank and 93 octane tune.
So, I say it will not hurt your motor, but to really get the "bang for the buck", get a tune to go with the 93 in your tank.

candymanjl

higher octane fuel will always runs smoother and more importantly it'll be cleaner. cheap gas dirties up valve train and cylinders so fast it's crazy. I'd personally never run anything other than 93 just to keep everything clean and have a smoother idle. to me it's not worth the $0.20 (which is only about 7% savings) to have a dirtier motor.

it's already been said but you don't have to run the same octane that your tune is for, you just can't run a lower octane than what your tune is for. as long as you're running the same or higher then you're fine.

ski

The knock sensors pull timing only up to a certain point. I've read numerous posts from S197 GT owners who have experienced pinging with a bone stock setup and 87 octane. Some were able to solve the problem by using a different gas brand, while others had to use higher octane gas to eliminate the pinging.

ski

Numerous engines unknowingly experience carbon build up regardless of which brand of gas or octane rating is used simply because the owners habitually either drive short distances that do not allow the engine to warm up to normal operating temperature, or they warm up a cold engine w/o putting a load on it by allowing it to idle with the car just sitting in the driveway.

Leoleo

Unless you have it tuned for 93, it will NOT run smoother. In fact you will not be igniting all the fuel air mixture in the cylinder and will not be cleaner. You will be putting un-used gas out the tail pipe. Differently NOT cleaner and a waste of money.

Nuke

+1 on dumping money out the tailpipe. Yeah, it may feel a bit smoother but that's more likely your subconscious trying to justify the added expense. Absolutely no significant HP increase (you might see 1 or 2 RWHP IF the PCM can adjust enough but no Seat-Of-The-Pants gain). Get a CAI & tune combo and even the 87 custom tune will net roughly 15 or more RWHP.

There are some that claim that running higher octane fuel than what the engine can handle can cause long-term detrimental issues but I haven't seen anything verifying that.

157dB

If the OEM timing tables wont allow it to
pull the timing enough for 89 octain to not ping,
then its less than 89 octane fuel...
So stepping up to crap 91 gives you the 89 thats
needed for a no ping cruise...