|Yesterday 12:48 AM|
|07-22-2015 11:29 PM|
|07-19-2015 04:47 PM|
We've discussed this behind the scenes quite often when it comes to threads that have increased in size. There's no real 'good' solution, unfortunately. It's frustrating for one guy to read through all or the majority of a thread; it's frustrating for everyone else when someone is too lazy to try. It's like walking into a half hour conversation that two people were having and then expecting them to start from the beginning just for you as opposed to watching a recorded version of what they said prior to jumping in and trying to be part.
A weak example, but still.
Are you going to offset the cost of the fuel by mileage savings? That's dependent on a lot of variables, unfortunately. I always encourage everyone to do their own testing with the fuels that are local and convenient to themselves. Not only are there differences between octanes, there are differences between the same octanes and different brands. If there was a simple and easy answer then people would give one, but there's not so they can't.
|07-19-2015 02:32 AM|
|07-18-2015 08:53 PM|
Angry thread merged with previous thread.
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.
|07-16-2015 09:04 AM|
|07-14-2015 01:02 PM|
I suspect you had a tailwind.
I don't experience notable increases in MPG when switching from 87 octane to 91-93 octane. I do, however, experience a notable improvement in stop-and-go driveability when making that switch. Therefore, I use 93 octane unless I know the majority of my tank of fuel will be highway miles. If I am driving strictly highway for a fillup, I will buy 87 octane.
|07-12-2015 06:44 PM|
Sorry for the thread resurrection, but I just ran an experiment during a highway drive.
I usually run 87 octane in my 2014 Titanium 5 speed, and for a long (250 mile) highway drive I did an experiment with 93 octane.
While sticking mostly to 70mph I managed to get 42.2 MPG average for 100 miles, then got down to 41.1 MPG average when the terrain started going steadily uphill for the next 100 miles.
I am not used to getting much over 36mpg on the highway with the 5 speed, even babying it at the speed limit like I was this time.
Are these the numbers you guys are seeing when using the premium gas (and the MTX-75 5 speed)? Again, this was purely highway cruising.
I am taking a road trip from Michigan to Virginia to Pennsylvania and back to Michigan starting this next week. I may continue my 93 octane experiment to see what MPG I can achieve at different speeds.
My car is currently at the 7200 mile mark on the odometer.
|07-03-2015 02:55 AM|
|FFhb13||I'm going to switch over to E85 and see how that goes for a while, and I also do plan on running higher octane, been running 89, haven't noticed any difference so will try 91|
|07-02-2015 04:39 PM|
|Jburks||what it comes down to is higher octane is better and if you are willing to pay the extra couple bucks a fill up then you should definitely use it. There is no denying you will get more power and better mpgs with higher octane gas. that is a fact, period. however, you will not hurt your engine by using 87 octane so if the cost is not worth it to you then you will be fine. i have used 92 octane in my car since day one and will use it as long as i have.|
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