Gas Mileage for lower octane

[evan546]

the reason i asked this question in the first place is because im considering taking my car on a road trip to orlando which was 223 miles both ways i saw that one forum member was getting 500 miles to empty on a full tank and i wanted to see if i could make it there and back on one tank that would be cool.

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[evan546]

Dont get me wrong i drive this car how its meant to be driven....addle:

 

[ElAviator72]

No, you must be driving alot of city/hard.
I use my ecoboost to commute, mostly hwy (3.55 gears), i run 93 octane and get routinely close to 400 miles per tank when i fill up.
i hand calculate my mpg (miles driven/gals of gas to fill up) and consistently average 27+

Same here. I'm consistently seeing about 27-28 MPG on the commute (mine's a stick). I fill up with Premium (which is typically 91 or 92 octane around here...). Unfortunately, Oregon requires 10% ethanol year round, so I'd probably be getting mileage if we didn't have such a high ethanol mix :tsk:

 

[ElAviator72]

When I was test driving Mustangs, every single Ecoboost I drove showed 12.1 MPG...gee I wonder how people drive a Mustang on a test drive

 

[turtleboy]

Better mileage, no, lower hp, yes. If its only 2xx miles round trip, just use whatever grade of gas you are using now.

 

[Rough Hollow Man]

My 2015 V-6 got 24.9 MPG for the first 1000 miles. But just to see if the engine behaved differently, the second 1000 miles I used 93 octane...I got 26.1MPH...a 1.2 MPG difference. I drove it the same. I used the running onboard computer for the total 2000 miles. I do not think the extra expense of premium is worth it for a 1.2 MPG gain. I just wanted to see if it made a difference at all with the 3.7 engine. Going back to the regular unleaded from here on out.

 

[paullyd210]

the reason i asked this question in the first place is because im considering taking my car on a road trip to orlando which was 223 miles both ways i saw that one forum member was getting 500 miles to empty on a full tank and i wanted to see if i could make it there and back on one tank that would be cool.

I'm pretty sure you can I recently went on a road trip from San Antonio to St Louis MO using 83 in my friends EB non-tuned we averaged about 80-85 mph hitting 100 at some points and were able to get about 390 miles in one tank. Go 60-75 mph and you'll be fine

 

[Skenneyjr]

Premium has higher octane which means the engine can run more advanced timing on more boost and make more power for a given amount of fuel. The ECU is smart so you can run regular....but you'll get less power and it will run retarded timing and possibly even a bit rich because fuel cools the charge and a bit of richness can help prevent detonation. My old turbo coupe went pig rich under boost because technology wasn't as good in the 80s and that was what they could do to prevent detonation reliably.

Almost any modern engine will see a fuel economy increase with higher octane fuel even if it's meant to run 87. The ECU is tuned to run at optimum efficiency which means most of the time running right on the threshold of engine knock. 93 gives more room before you hit knock, so the ECU will add timing or lean out a hair to gain efficiency.

Ethanol content is also a huge issue. Same grade, same driving, e10 or e0, e0 will net as much as a 10% increase in economy. In my dad's 2012 F250, he went from 14.5mpg average on e0 to 12.8mpg on e10. 1.7/14.5 is a pretty dramatic change....especially since the truck put on 25,000 miles a year.

Unfortunately around here, my choice is 91 octane e0 hovering at $3.15/gal or 93 octane e10 at $2.60/gal. I've been running the 91 and getting 22 when I didn't waste half the tank doing stop light drags on main street. Switched to the 93 and so far averaged 26 for a while, dipping to 24 when I started being silly again. Octane might be more important than ethanol for me.

Bone stock BTW. Ecoboost, PP, 6 speed manual. My driving is about 60% city 40% highway with an aggressive fast driving style. Most of my highway driving is at 90 and on the current tank my trip average running an average speed of 105 somehow showed 26.2 mpg average for that trip. Don't know how it did so well considering drag increases as a square of Speed but whatever.

 

[Skenneyjr]

Are you guys saying 83 like 83 octane? Big no-no. Ford says 87 minimum. Hell, in Nebraska, it's illegal to sell less than 87 as road fuel.

 

[ElAviator72]

Are you guys saying 83 like 83 octane? Big no-no. Ford says 87 minimum. Hell, in Nebraska, it's illegal to sell less than 87 as road fuel.

Wish that was the case in more places...lots of folks down in the Southwest get taken advantage of (I've seen pump octane ratings as low as 85...). causes you to needlessly purchase mid-grade in many cars. Texas (far West Texas, like El Paso), New Mexico, and Colorado come to mind on that one No excuse in El Paso, especially, because the refineries are in town, and you can't argue that the altitude is higher at the gas station (the octane rating you see on the pumps is measured at the filling station).

 

[dgc333]

Almost any modern engine will see a fuel economy increase with higher octane fuel even if it's meant to run 87. The ECU is tuned to run at optimum efficiency which means most of the time running right on the threshold of engine knock. 93 gives more room before you hit knock, so the ECU will add timing or lean out a hair to gain efficiency.

I will disagree with that statement. No matter how agressively you drive, the vast majority of your driving is under light load where the throttle is barely open. Under these conditions detonation is not an issue and the ecu can add timing as needed without extra octane in the fuel. I would agree you could see a mileage improvement at the track but not in every day driving.

This has been proven over many miles with our 12 Focus, 13 Focus ST, 14 Dart and 15 Ecoboost Mustang.

 

[madweazl]

Higher octane fuels burn slower and provided all things remain equal with the exception of the fuel, you should see an increase in MPG with higher octane fuel.

 

[Skenneyjr]

I will disagree with that statement. No matter how agressively you drive, the vast majority of your driving is under light load where the throttle is barely open. Under these conditions detonation is not an issue and the ecu can add timing as needed without extra octane in the fuel. I would agree you could see a mileage improvement at the track but not in every day driving.

This has been proven over many miles with our 12 Focus, 13 Focus ST, 14 Dart and 15 Ecoboost Mustang.

The ECU will lean out and advance timing to get maximum power from the fuel. Higher octane allows more timing and leaner burn before you hit detonation. Higher octane fuel, as long as it didn't gain octane by ethanol, will net greater mpg.

 

[dgc333]

You are confusing what happens at WOT high load conditions and what happens at light load cruising where you spend the vast majority of your time. It is the light load cruising that determines what your overall gas mileage is going to be.

At cruising the throttle is barely open, there is no boost, the ecu is running closed loop keeping the mixture close to schisometric (14.7:1), the ecu is adding a lot more timing than the engine could ever use for max power and the engine is least likely to knock and does not benefit from higher octane fuel. These are the conditions that determine the over all mileage you will get from a tank of gas, not the occasional 1 to 4 second blasts at WOT.

Back in my early hot rodder days when all cars had carbs and distributors mid 30 degrees of timing (depending on engine) was what you needed for max power but you would need upwards of 50 degrees for best economy while cruising. Distributors had mechanical advance that was rpm based and is what determined the timing for max power and a vacuum advance for timing under load. So at WOT no vacuum advance but at light load cruise when manifold vacuum is at its highest you got max vacuum advance on top of the rpm based mechanical advance.

BTW, adding advance DOES NOT automatically mean more power. Again depending on the engine max power occurs when max cylinder pressure occurs around 20 degrees After Top Dead Center. To little timing and max cylinder pressure occurs later than 20 ATDC and power is reduced. To much timing and max cylinder pressure occurs before 20 degrees ATDC and power is reduced.

Before the use of CAD tools intake runner and chamber design was a trial and error thing and engines were very suceptable to detonation. This was controlled by retarding the timing and use of higher octane gas. Today with modern CAD tools the trial and error all occurs on the computer before a piece of metal is touched. Today's engines are much more detonation resistant, require much less timing which is much closer to ideal and generally need less octane in the fuel. While the old hot rodder tuning tricks of running higher octane and more timing still work the gains are minimal in a NA engine. In a boosted engine because of the generation of a lot more heat higher and more detonation suceptablity, octane will allow for more boost netting significant gains

 

[Wblv17]

I'm pretty sure you can I recently went on a road trip from San Antonio to St Louis MO using 83 in my friends EB non-tuned we averaged about 80-85 mph hitting 100 at some points and were able to get about 390 miles in one tank. Go 60-75 mph and you'll be fine

so from san antonio to st louis all on 83? I call bull shit, never seen less then 87

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