Proof premium fuel is better.

[green_henry]

Can you add e85 without the e85 tune?

I run 3-3.5 gallons of e85 topped off with 91 most times I fill-up (I have to go a little out of my way to get e85)

 

[Spork1569]

I run 3-3.5 gallons of e85 topped off with 91 most times I fill-up (I have to go a little out of my way to get e85)

Isn't that effectively making E30? Do you run a stage 2 tune or an E30 tune?

 

[green_henry]

Isn't that effectively making E30? Do you run a stage 2 tune or an E30 tune?

Yep, it's ~E30. I run a stage 2 91 tune because I'm not sure that the supply of e85 is going to be convenient or reliable -- it's about 9 miles to the nearest station, and I'm worried that they might stop carrying it.

 

[Snrub]

It is not sprayed on the valves directly as in a port injection engine. Have a read of the study. Top Tier

Fuel never hits our intake valves unless people are adding aftermarket port injectors, so it's not relevant to most Fiesta ST owners.
View: https://youtu.be/LjJSbHxIvnM?t=99

When I first read the AAA study, I must have skimmed the 2.3L part and thought it was the modern Ford engine, not the one from the 80s. I guess I assumed when the valve was closing a certain amount of fuel mist might end up on the outside. I read last night, that in reality that type of behavior would result in higher deposits and they try to avoid it. So no cleaning effect for existing deposits.

 

[TrickSTer]

I hate to repeat myself but facts never go out of style

The more octane a fuel has the harder it is to combust. This means timing can be advanced closer to TDC thus making more power on the power stroke.

Correction: The more octane a fuel has, the less it will be prone to pre-ignition; pre-ignition manifests itself as "knock". (it's easy to combust fuel; you just introduce a spark. Higher octane: less knock (pre-ignition): automatically advances timing more BEFORE TDC.

 

[scooter123]

To clarify what Trickster has said 4 cycle gasoline engines have the spark plug start the combustion process BEFORE the piston is at TDC. Because ideally you want the combustion to reach it's peak at a point a bit past TDC so that the full burn takes place during the power stroke. How much far in front of TCD (advance) is needed is dependent on many factors, some of which are piston speed, charge temperature, and fuel octane.

If you have too much advance then what happens is the the fuel charge can start reach the critical temperature and pressure before TDC. As the piston compresses that burning charge the chemical process can then change from Combustion to Detonation. BTW, Detonation really is an Explosion, as in a Dynamite type of Kaboom. In the case of our Fiesta it can blow a hole thru the top on a piston quicker than you can snap a finger.