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Topic Review (Newest First)
Today 12:06 AM
RonMaiden I'm still curious about coldbear and the 300,000 miles on his 2014 SE.
Yesterday 10:01 PM
Originally Posted by Blackfocus86 View Post
I've ran 87 and 91 from 76 here in Cali Los Angeles. Same gas station same commute to work. Tried 91 cause I read someone here got a 4mpg increase. What a bunch of bull my mpg was the same with both gas lol. I manually calculated my mpg with 95percent highway at just over 70mph 36mpg with both gas. Will also add how inaccurate the mpg calculator the car has is. Been off anywhere from half a mile to 11 miles off lol.
I just went ahead and quoted my post from earlier as it fully explains why people with any majority of highway use won't see gains. You're right, you should just keep using 87 if your sole concern is cost per mpg. Most of it will be a waste for you to read so I just made your pertinent section bold and underlined it.

Originally Posted by dyn085 View Post
The explanation for why there is a benefit is actually pretty simple, and that's because Ford incorporates dynamic timing through the use of knock sensors, an Octane Adjustment Ratio (OAR) learned number and a table for which to multiply against in order to offset timing. The sentence itself sounds difficult, but it's pretty easy. A very quick breakdown-

OAR starts at 0 and is learned in two directions, positive (low octane) and negative (high octane). This gives it a total scale of 1 to -1. This is achieved by monitoring knock sensor (KS) feedback and the timing adjustments that are made accordingly.

The OAR Compensation Table is a timing compensation table with zero or negative numbers at each RPM/load cell. This is located in the borderline ignition tables and is what the OAR learned number multiplies against. The results are then applied to the base timing map being used.

Ok, that means nothing to people that can't see the programming. Here's how it works in practice-

While accelerating, the KS are monitoring each cylinder for knock. If no knock is present then it begins advancing the timing up to whatever the Mk3 KS limits are. The OAR system monitors these timing adjustments and shifts the OAR number towards the negative scale accordingly.

Now that the OAR learned number has shifted towards the negative, there is a compensation that can occur. As an example, if the compensation at 1k rpm/.8 load is -5 then that -5 is multiplied against the OAR number to result in the timing compensation at that specific rpm/load. This compensation is applied to the base table and the next time the vehicle accelerates the timing is now more advanced than it was previously, giving the fuel more time to burn through each stroke.

This continues until either the OAR maxes out at -1 or until the compensation is drastic enough to cause the KS to pick up knock. If knock occurs and timing is reduced drastically enough the OAR moves towards the positive. It doesn't have to max out in either direction and will settle out accordingly based on the fuel and average driving.

This process occurs nearly continuously depending on the fuel used. Good fuel will max out the OAR and achieve the maximum timing advance programmed while poor fuel can do the opposite, and I've seen up to a total of ten degrees worth of timing compensation difference on the stock ST tables between low and high octane. Obviously I don't know exactly what the Mk3 has available, but it will be similar because Ford uses the same Master ECU on its platforms.

I always wondered why highway travelers didn't really see the same benefits that city people did when it came to mileage, but after being able to see the programming I understood it much more. The MBT tables, which is where you 'cruise' at (low/consistent-load), have no OAR compensation-the timing is exactly the same for both 87 and above. Only the borderline tables have the OAR compensation, which makes sense because the only times you're really going to see benefits from using a higher octane are going to be when the engine is under load and there's more heat and pressure within the cylinders.

Tl;dr-Ford utilizes dynamic timing in their current ECU's. Kinda useless for someone that has a flat highway commute but beneficial for those that have a lot of acceleration or higher-load (climbing/passing) driving.
Yesterday 03:38 PM
sailor It's def. a 'results may vary' situation, and even the diff. between your local fuel at 91 vs. somewhere else at 93 can make a difference.

Heck, in some localities 93 is 100% gasoline with 87 being 90% (E10) so that can affect it as well - not just octane.

I mentioned the number of tanks for general reference since most have a LOT left in their tank when the light comes on. Mine comes on at about 9 gal. used, at least intermittently, out of 13 capacity and a max of 12 used for the LOWEST I ever took it.

9- 10 fresh with 4-3 remaining is a noticeable dilution.

For your use, in your region, it doesn't make sense to pay the extra.
Yesterday 03:24 PM
Blackfocus86 Yea. I run my tanks down till the gas light comes on lol. I ran about 15 tanks of 91 and 15 or so 87 all calculated. Big difference also driving south to work and doing little trips up north. Going down to Newport Beach and back to la about 36mpg. Going up north to the valley then coming back to La about 41mpg. Amazing stuff huh lol. But definitely no difference in mpg. Waste of money. As far as far running better on 91 from the pants on the seat felt the same to me. Then again I don't go racing or driving quick
Yesterday 02:24 PM
sailor It's not easy to get a good comparison, have to change over and run something different for a number of tanks before getting any decent comparison.

Initially it's just a partial one, since the fuel is mixing with what was already in use.

Often a fair variation without a change as well, just due to different driving done on each tank full.
Yesterday 02:12 PM
Blackfocus86 I've ran 87 and 91 from 76 here in Cali Los Angeles. Same gas station same commute to work. Tried 91 cause I read someone here got a 4mpg increase. What a bunch of bull my mpg was the same with both gas lol. I manually calculated my mpg with 95percent highway at just over 70mph 36mpg with both gas. Will also add how inaccurate the mpg calculator the car has is. Been off anywhere from half a mile to 11 miles off lol.
02-22-2017 11:19 PM
Slicknick I ran 87 when I was strapped for cash, the reason I bought the focus, but now I paid the car off. The car ran just, well...okay. I never thought I would be running 93 in this car but after I got a few mods and a tune I had to try it. Premium will cost me an extra $250 a year and it is worth it for me.

If you plan to keep the car for awhile, which I do, I would get a 93 tune. Car runs spectacular!
02-22-2017 05:44 PM
DJTrollin I was using 87 but was getting a slight staggered pinging noise when I opened the car up. Switched to 93 and the sound has went away. Currently intake, headers, Tom's tune and exhaust.

Sent from my MotoG3 using FF Mobile
02-22-2017 05:26 PM
Jburks you have 300k miles on your car?!
02-22-2017 04:17 PM
((( 89 )))

I use 89 octane in my 2013 SE. It takes a couple tanks for the computer to get use to the higher spirits. Best money one can throw at the FF beside full synthetic. 300,000 miles, she's hummin' right along ....!
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