Long post...
cheezsnake said:
The octane rating of fuel is simply a measure of its resistance to pre-ignition, or knock. The higher the rating, the more resistant it is to pre-ignition. Unless you start increasing the cylinder head compression (where higher octane is needed to avoid knock), you probably aren't going to see much horsepower benefit from using higher octane gas.
This definition of octane is exactly correct. Octane is the ability do resist detonation or pre-ignition (Yes, two different but similar problems).
Detonation is spontaneously igniting the mix prior to the spark event (Due to high cylinder pressure). Pre-Ignition is carbon or some hot spot igniting the mix prior to the spark event (Most likely on high mileage engines). The "pinging" sound you hear is the two flame fronts colliding. Cylinder pressure is abnormally HIGHER and can cause damage. To keep it simple, the higher octane fuel burns slower.
Our cars and designed to run 87 octane, and you should see the best performance by using it... Faster burn, more power... No detonation, more timing... Again to keep it simple.
Now, I posted on this thread because I had already intended to ask you guys and girls if detonation has been experienced with the STOCK PCM calibration.
I had light detonation when going WFO (WOT to some). No detonation is acceptable to ME, as a Ford tech. Please understand that EEC V (Our computer) has adaptive strategies to retard timing and lean fuel curves based on the LOUD PEDAL and how you use it (I like to feel the power daily... LOL). Drive like your grandmother, and you drive the PCM to go lean and back off timing for economy. In addition, if detonation is sensed by the PCM, timing is retarded through the adaptive strategy. This does take a drive cycle or two... Not necessarily immediate.
With that said, and knowing I only have 2K miles on mine and want to have NO problems, I tested 89 octane. No more detonation, so I feel more confident with WOT. What I think is, based on the way I personally drive (Mostly in a legal manner), I ended up allowing the PCM to lean the fuel curves, so when I powerslide into a turn, I noticed the pinging noise. Mostly under heavy load (100 %), and tires hooking though. If the tires get blown away, there was no perceivable detonation (The system goes RICH when you mash the LOUD PEDAL).
Knowing Ford, IF this becomes a wider spread problem ("X" number of cars detonating), they release a revised PCM calibration or software version upgrade. I am not saying this is the case, just stating what I have seen while working with these systems in the dealership. No cause for alarm.
So I am asking if anyone notices any detonation first, and also reiterating the fact that you will want to use 87 octane if no issues occur, for best performance and lower fuel cost. You should NEVER need 91 or 93 octane unless you recalibrate or add a supercharger or turbocharger. At that point, custom tuning is required anyway.