which octane fuel is best for your Stang?

[rude_life]

I have a 1995 Mustang GT w/ auto trans...NO mods whatsoever. 139k miles. I have owned two other Stangs both moderately modified. I used this forum a lot when I had the other stangs..
I have read a lot of people on here say that the motors are tempermental and some have theorized a poor factory tune is to blame for the widespread preignition/pinging problem. Well I have had this paricular mustang since January and havent done any work to it. I have always thought the car was kind of slow, slower than it should be.. and have suffered constant pinging sometimes very terrible sounding and always ran 91 octane.
Since the day I got it I have ran 91 octane fuel in it as opposed to 87/89 octane due to what I have seen in here it sounds like you kind of have to run the 91 in the 94-95 5.0 motor. Well yesterday I had to drive to LA which is about ap 60 mile drive..the last day before that I had for the first time put 89 octane in it because my buddy pumped and accidentally selected 89 octane..and she seemed to run better... Less pinging, "lighter on her feet". Well to make it cheaper for the drive to LA I ran all 89 octane again, and an Obvious difference.. again.. considerable less pinging.. more power.. lighter feeling. By the time I got back to town it was cool out.. mid fifties degree wise. And the car ran stronger and virtually ping free still.
Well today is day 3 and used the 89 again.. and the car is running stronger and basicly ping free.

*My question is:
Could the 91 Octane that I thought was helping actually not good for my car?

 

[revhead347]

I can't imagine. My old engine really wasn't happy until I put 100 unleaded in it. It loved that stuff.

Kurt

 

[ratio411]

Higher than necessary octane is NOT a performance aid.
The higher the octane number, the LESS volitile gasoline is.
For best performance you must run the lowest octane possible for your particular engine.

I can't imagine why high octane was giving you ping...
That said, the car was meant to run on 87, anything higher is a waste of money, contrary to what the fuel companies would have you believe.

 

[revhead347]

If you bump the base timing way up like most people, it doesn't like to run on 87 anymore, but I can't see that being the issue.

Kurt

 

[toyman]

Before my mods I only ran 87 octane with timing set at 14* and never had a pinging issue. The thing to check as the cars age is the HB. The bonding agent between the inner and out hubs deteriorates which can give you a false timing number when checked.

 

[95snoozer]

i would run the highest octane (91 or 93) and timing at 14*

if your timing is stock, run 87.

The pinging in the 94-95 is not due to fuel quality normally. carbon build up on the heads is an issue, as is the stock timing curve of the computer. Too much part throttle timing near peak torque.


Run some seafoam treatment possibly as well and save yourself a few bucks a month and run 87 if you arent messing with timing.

 

[BlackVert]

mine needs high octane.