octane rating and engine performance
In Texas, the minimum octane rating is 87. On a recent trip to Glacier, I noticed a lot of the fuel in states like CO, WY and MT, the octane was 85, and you had to buy the mid-grade to get 87 and abov...
Forum Discussion
Lynnmor wrote:
We like to think that the engine can compensate for poor choices in fuel, but forget that the compression ratio cannot be adjusted. The Ecoboost engine is just one example of turbocharged engines that must lower boost, again to compensate for low octane fuels.
I don't know how Ford should write a manual, because even limiting words to non-technical confuses the masses.
I think you are applying the limitations of port injection to direct injected engines. Direct injected engines can run at higher compression ratios without the need of higher octane fuel because it can better control injection timing thus deterring knock or pre-ignition.
I would do some more reading up on how direct injection differs from port injected limitations. Here are some great articles to start with.
DI Engine Guide – Direct Injection
Explained: Direct Injection Piston Design and Tuning Theories
Notice in the first article where it states that direct injection engines can run a higher compression ratio than a port injected engine by ten percent. This is why other direct injected N/A engines like GMs 4.3L and 5.3L can operate on 11.0:1 compression ratios with 87 octane. The GM 6.2L has an even higher compression ratio of 11.5:1, but GM requires 91 octane fuel in that truck.
