Gas and Tires

[Laga]

So the increase in timing is basically the safety margin from factory?

From my understanding, it’s a combination of emissions, warranties, and fuel economy.
The factory dials things back to meet the above goals.
They have gotten better over time as the gains from a new tune on today’s cars are not as large percent wise, as the gains I saw on my 05.

 

[Juice]

“Engine Masters” took a NA LS engine and tuned it for maximum performance on 87 octane. They then changed the fuel octane rating 3 times. 91, 100, 114, and tuned those for maximum power. Not only did all levels of octane produce the same amount of HP. The timing for max power remained the same. It depends on the design of the engine for how much HP it will produce.

EM only tested max power, WOT. Part throttle medium load driving is where too low of octane fuel will knock or potentially cause damage. They should have done a steady load/rpm combo, like half throttle and 2500 rpms, and than do a timing sweep. I bet there they would have seen differences in the fuels.

 

[GriffX]

EM only tested max power, WOT.

I have seen it now, they used carburetors so all other than WOT is hard to compare to an EFI anyway, or?
My Mercedes decrease ignition from 35°C IAT on, don't know where the threshold at the Mustang is.

 

[Juice]

I have seen it now, they used carburetors so all other than WOT is hard to compare to an EFI anyway, or?
My Mercedes decrease ignition from 35°C IAT on, don't know where the threshold at the Mustang is.

Efi vs carb they have compared. Carbs make a little more power vs efi due to cooler intake charge. But cyliner to cylinder fuel distribution is poor vs efi, and you cant do a whole lot about it. (and most carb guys dont even know without 8 WB O2s) EFI can do individual cyl fueling.
No reason you cant do steady state tests with a carb.
As for timing, thats totally dynamic on these new cars. Way more complex than just pull timing at a certain temp.

 

[MrBhp]

If you have a engine designed for 87, increasing octane usually reduces power. If you have a engine designed to run on 94 and run 87 you are going to have problems.

Not necessarily. At least if you're considering a newer designed, computer controlled engine. The inherent safeties that are built into engine control GENERALLY allow for a broad range of conditions, such as a widely varied octane rating. Of course, if you build an engine with a very SPECIFIC octane rating, and run that engine on the edge of detonation, (where most performance engines really scream) the lower octane may cause severe damage. And running the other way around is just silly. I have friends who swear their N/A Corolla runs better with 93 than with 87. I just don't see how that it is possible.