I don't understand this engine knock business in regards to the Ecoboost since it was designed to run on 87 octane which is also the recommended octane.
I've used 91 for several months but went back to 87 since there was no change in MPG and no perceptible change in performance.
Peter
pardon my bluntness but no it's not. read the ecoboost specs and your manual again. Those HP and TQ numbers show with an asterik to say on preimum 91 octane only.
Yes it will run on 87 - so will my GM built LS3 - but both engines perfer preimum higher octane gas.
Why - knock and pre-detonation. when you run higher compression, or spin a hot huffer (turbo) you heat up the intake track and the air in the cylinder. you can get the air so hot, the fuel when it hits ignites early. Now someone's going to come in here and say but but the ecoboost is a DI engine.
yes it is - direct injection - pushes the fuel in the cylinder directly, not down the intake air track.
However - engine designers for both engines have power and combustion effeciency targets and the like and they will use a term call flame front propogation. Image you stike a match - it flames up - that same thing is supposed to happen around your spark plug when it fires. AND ONLY WHEN IT FIRES.
with lower octane fuel - and higher compression, or rather hotter air in the cylinder - that fuel air mix might ignite before the spark. EVEN IN A DI engine. This is bad for many reasons and the biggest is impulse loads against the valves when they aren't quite in design position. IE hammering the valves when they aren't fully closed or where they are supposed to be - let alone where the engine computer wants the ignition moment to occur.
SO to account for lower octane fuel - the engine designers have the computer do adjustments so as to prevent engine damage - most notably these adjustments include.
Shifting spark timing, Cam phasing (the VCT part of the TI-VCT engines which includes the ecoboost) and most specifically the biggest adjustment is air/fuel ratio. shifting the mix altogether - prevents detonation timing issues.
however it drinks a touch more fuel, which also creates a touch more exhaust gasses, and more soot/carbon nast on the insides of the valves, runners, injector tips etc.
This is a side effect on all engines - but 2 key issues are the intake air temp and density (read that more as humidity). if you have cold dense air, there's little to no adjustment, if you have hot humid air, there is some adjustment. If you have hot, dry air - there is more adjustment.
Now the average person won't notice when they are down 20hp or so, and they often might not even notice 0.5mpg differences - especially in summer heat when you'd chalk it up to more AC use. the effects of how 87 octane changes your performance vary with how you drive the car also. I tend to hammer on my performance car a bit more - so when I put 87 in it - I noticed a 1-2mpg drop and sluggishness. In our older focus - in august heat - 87 vs 93 was a 2mpg drop.
in the explorer - I bet it's a mostly non-event for the TI-VCT 3.5, on the ecoboost I bet it's a bigger effect.
More importantly to the OP and his ecoboost engine - this will effect your fuel dilution numbers and the extra carbon, calcium and other remnants in your oil analysis. OR rather - It could show up in there. note could, depends on how you drive and the out side air temps.
hope that's a bit more clear.
