No mods on car 91 . I tried several gasoline brands and several octane ratings . Is there any positive or negative effects of brands and octane ratings ? Is the 87 octane better for full detonation on a non modded 5.0 ? Does it burn hotter and will it increase engine temps ? Will the stock Computer under WOT automatically advance the timing to a higher degree if higher octane is used ? I know most everyone has mods done and for them it may be different , but my car is just a clean stock daily driver . Thanks
Lower octane burns quicker and more complete. Higher octane just resists burn, so it helps combat pre ignition when used in power adder, or modified applications.
Ideally, you want to run the lowest octane you can get away with without detonation (pre ignition). If you are bone stock (timing set to 10 degrees), stick to 87 unless you have detonation. Detonation in older cars can be caused by carbon deposits on the heads if the engine is rather dirty. So in some cases you may need to run 89 octane or so to avoid this.
What if you set your ignition timing more advanced on a stock setup. When mine was stock I bumped the timing to 14 and felt a noticeable improvement in performance. 93 octane can help fend off spark knock of more advance timing cant it?
10 degrees base timing is where Ford set it from the factory and based its ECU programming on. You get lower emissions and reduced chance of detonation in most driving conditions. In other words it's safe for most average driving conditions and won't damage the motor
Bump the timing and power goes up, but also some negative side effects such as increased emissions and detonation...hence the need for higher octane.
Scope of this thread is really towards stock cars.
Preignition is typically caused by a heat source in the cylinder, like the ground strap on a plug with too high of a heat range. Detonation is caused when the flame front causes pressure/temperature in the unburned end-gasses to rise over the auto-ignition temperature of the fuel. Higher octane = higher auto-ignition temperature in a given fuel type. Hence, higher octane resists detonation, but this can also be accomplished by cooling the A/F mixture before the spark or by running a richer mixture that resists detonation through evaporative cooling, which ultimately keeps the end gas temps down below auto-ignition temp.
Preignition is deadly and instantaneous. The fuel typically burns completely as the piston is still rising to compress it. Detonation can be deadly, but mild detonation typically is not, at least initially. Detonation unchecked can lead to preignition as pieces of piston, plug, ring, head or other material is picked off and remains as a "hot spot" in the cylinder that potentially ignites the incoming mixture. Obviously, unless you are tuning on the ragged edge in an engine-masters shoot-out, you don't want detonation, either.
Answer to title question for a good condition stock engine, including timing as Mike stated, is no.