Originally Posted By: Hokiefyd
Originally Posted By: AP9
Originally Posted By: Peted
Secondly, most posters in this thread have experiences that tend to state otherwise.
That being, even if a vehicle recommends 87 in the manual, the vehicle will run better on 93.
Not to be a smartbutt, but . . .
Most posters in this thread have experiences that tend to state otherwise. Go ahead and add me to that list: zero difference in fuel economy or performance on a Ford Explorer with 4.0L OHV V6 (compression ratio 9.0:1) between Shell 87 & 93 octane. At such a compression ratio, the engine is normally not close to knocking, so a more knock-resistant fuel offers no performance advantage.
I think Peted's statement is more correct if "will" is changed to "may". Even if a vehicle recommends 87, it MAY run better on 93. Some folks in this thread are speaking in absolute terms, and there are too many variables to do that accurately.
AP9, to your Explorer's engine, there's more to knocking than only the compression ratio. Ignition timing also plays a part. My Oldsmobile's V-8 engine (8.0:1 compression) would knock if I had the timing advanced too far. I'd say that it's likely that your Explorer automatically advances and retards timing, and that the maximum advance and maximum retard are set in the computer. It should be possible for your V-6 to knock on 87, if the timing were to be advanced that far. And if that were true, then it should also be possible for your V-6 to experience better performance on 93 octane.
Now, you've said that it doesn't. If it truly doesn't, then there's at least one explanation for that: your computer cannot advance the timing far enough to achieve that better performance on 93 octane. There's a direct correlation here with the aftermarket. You know those aftermarket tuning chips, the ones that often say that premium fuel is required? They're not increasing the compression ratio in the engine, or doing anything physical to the engine at all. They're simply advancing the timing beyond what the factory computer is capable of doing, thus unlocking the potential of a higher octane fuel.
So here again, because a vehicle's programming depends entirely on proprietary code written by the OEM, an accurate blanket statement cannot me made that says that a car either WILL or CANNOT run better on 93 if it recommends 87. The most correct answer is, "it depends". It depends on how that vehicle's software is written and how much timing advance is allowed in the computer.
I suppose. FWIW, the 4.0L OHV engine does not have a knock sensor, so no ignition timing retardation automatically from knock. Nor have I attempted to adjust the timing. It does adjust timing but not due to knock, rather due to throttle position, load, etc.
Originally Posted By: Peted
Okay, I went and added you to the 'list'. I counted all the posters who have used both 87/premium with cars that did not
require premium.
7 posters state no difference/worse performance on premium and 13 posters stated an improvement. Nearly twice as many.
The numbers don't lie.
Touche!