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If you read the whole paragraph its talking about the fact that in some regions regular is 85 octane and that using premium will give better performance than 85. It does not say you will get better performance than 87 octane.
Here's what it says on page 351 RE fuel ethanol/E85

During the summer season, fuel ethanol may contain a maximum of 85%
denatured ethanol (Ed85) and 15% unleaded gasoline. The fuel ethanol
has a higher octane rating than unleaded regular or premium gasoline
and this allows the design of engines with greater efficiency and power.


This basically says higher octane = greater efficiency and power.
 

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My Findings.
Premium 95 RON Worse Fuel Consumption, Less Low End Torque, Better Power at High Revs
Regular 93 RON Better Fuel Consumprion, More Low End Torque, Worse Power at high Revs

High Octane Gas has a higher % of Retardants to combat Pre-Ignition.
 

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I use 93 and have found a bit of an improvement from 87. Its a little more pricey, but when you only have a 12 gallon tank, its not a huge extra expenditure.

I'm coming from a 98 BMW 740i that I fed premium and had a 20 something gallon tank, so its still much cheaper then what I used to pay. Plus I'm only a semi decent stick driver, and am getting closer to 400 miles to the gallon then 300 now.
 

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What does the tank size have to do with the actual cost? Does it matter if your full fill up is 12 gal or 25 gal? The price per gallon is still the same.
 

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Yeah, but it's only coming out of your pocket 1/2 at a time. LOL Makes me feel good when I'm feeling up my Focus, About $50 every 3 or 4 days. My Saturn was $60 to $65 and my Murano was $85 to $100 every 3 to 4 days.
 

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Its true in a way, stock the car is "tuned" to run that gas. I believe they retard the timming to allow the cheap fuel to run ok in it.

You start to tweak it with a tune and you bump the timming way up and then the cheap gas starts to cause knock and then the car backs off the timming like in the pictures i posted.

When you get a tune it says premium fuel only and this is why because there IS a difference. It burns better, cleaner or something and im sold on the better gas now.

Why does the cheap fuel cause knock and what is it they put in it that does it? i dont know but i like my car so im not going to put junk in it if there is better stuff right next to it.

A few weeks ago i went to a cheap mom and pop gas station and i filled up with their premium because i was about out and knew i couldnt make it to my regular station. I swear i thought something was wrong with my car. It lost some of its zip i wasnt sure what was wrong it didnt run rough or anything it just didnt have the same zip it did.

After that tank was done i filled up with my normal 92 premium from the BP near the airport i usualy go to and i instantly felt the difference.

If i ever get in a pinch again with fuel im using just what i need to get back to the regular station and thats it.

Their premium must be low grade or something it just wasnt right.

I even had Tom tell me once after i posted a datalog and he asked me what fuel i was using because it was junk and it wasnt the same stuff i posted in an earlier log he adjust the tune to. This was early before i found a good fuel my car was happy with. The junk fuel was from quick trip at that time.
The graph you posted is pretty useless. Its just to cluttered and you really can pull any information our of it, the scaling is all wrong. When posting data logs its usually best just to post up a spread sheet. Its a lot clean.
 

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I've seen those favorably running 91 octane and those who have stuck with 87. I'm the middle-of-the-road guy who's running 89 and have seen welcomed improvement. Is this the best of boths worlds? Better performance and still reasonable cost?
 

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Running premium fuel allows the engine computer to advance the timing thus resulting in more power on the lower end torque curve, the burn time for higher octane fuel is also longer resulting in more power.
It would be interesting to see some dyno tests done with regular fuel and premium fuel.
Any of you that used to race will remember what quicker advance curves did for cars.
 

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99% of the time the gas is cut with ethanol to raise the octane, or the other 1% of the time additives that have vastly lower energy content than gas. Go look at the threads about people complaining about their MPGs dropping in the winter -- that's when ethanol content in gas is increased. Even if higher octane helped, you would have to see a 10% improvement in fuel economy for it to save you any money. That's a tremendous increase in efficiency, something Ford would have considered. Hell, most manufacturers switched to 5W20 to squeak a little bit more out of the engines. Ford put in radiator shutters to get an extra 3% efficiency -- why wouldn't they want a car that pulls down 30mpg in the city cycle and 42mpg on the highway? Even if people ended up using 87 and getting 28/38 instead, it would still make for great numbers in advertisements. Look at it another way; see the people running E85 and see what kind of mileage they get out of it. E85 is right around 96 octane (RON+MON/2) -- if higher octane = better mileage then logically E85 would be what everyone is filling their cars with instead of E85 being a cheap way to skirt CAFE ratings or for people that convert their cars for the massive power gains that are available. No one ever converts for fuel economy and actually gets it.

Will it make more power? Possibly, in situations that you have the engine running under a heavy load for extended periods of time because the engine will have knock issues. The compression ratio is extremely high in these engines and even in day-to-day stuff you'll have the occasional ping/knock. If you take it to an HDPE event, premium fuel is a good idea. Same goes if you're towing or load the car down in the summer months.

Any increase in economy is going to be from being conscious about getting better MPGs and being easier on the pedal. There's also the chance of carbon deposits building up quicker, but that highly depends on what additives are being used. Some cause it, some have a negligible effect. It's too soon to tell how these engines do with carbon buildup but virtually every other direct injection motor on the market has issues so it's something to consider.
 

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Here's what it says on page 351 RE fuel ethanol/E85

During the summer season, fuel ethanol may contain a maximum of 85%
denatured ethanol (Ed85) and 15% unleaded gasoline. The fuel ethanol
has a higher octane rating than unleaded regular or premium gasoline
and this allows the design of engines with greater efficiency and power.


This basically says higher octane = greater efficiency and power.
Actually, the above quote says that this fuel "allows the design of" engines with more power etc. It does not say if you put this fuel in your car that you will get more more or efficiency.
 

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Here's what it says on page 351 RE fuel ethanol/E85

During the summer season, fuel ethanol may contain a maximum of 85%
denatured ethanol (Ed85) and 15% unleaded gasoline. The fuel ethanol
has a higher octane rating than unleaded regular or premium gasoline
and this allows the design of engines with greater efficiency and power.


This basically says higher octane = greater efficiency and power.
Pg 351 is talking about flex fuel vehicles which i don't believe the 12 Focus is yet (mine isn't) so you can't even use E85. Typically flex fuel vehicles get about 25% less mileage compared to running it on gasoline and make less power too.

Yes, an engine designed to run on just E85 can have very high compression allowing it to make more power but because E85 has less energy content than gasoline will always use more. But a flex fuel vehicle is designed to run on both gasoline and E85 so it can't be designed to take advantage of the 100+ octane rating of E85, still needs to run on 87 octane gasoline.

So, "higher octane = greater efficiency and power." is wrong when it comes to the Focus.

My comment was in response to the first paragraph under "Octane recommendations" on pg 354. Where the sentence; "Premium fuel will provide improved performance." You can't take that out of context from the rest of the paragraph.
 

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My comment was in response to the first paragraph under "Octane recommendations" on pg 354. Where the sentence; "Premium fuel will provide improved performance." You can't take that out of context from the rest of the paragraph.
I incorrectly read what I posted. I agree with you about page 354, but beware, there are some who seem to take that sentence way out of context and make it something it's not.
 

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Running premium fuel allows the engine computer to advance the timing thus resulting in more power on the lower end torque curve, the burn time for higher octane fuel is also longer resulting in more power.
It would be interesting to see some dyno tests done with regular fuel and premium fuel.
Any of you that used to race will remember what quicker advance curves did for cars.
Adding advance does not necessarily mean more power. To get max power and efficiency maximum cylinder pressure needs to occur approximately 20 degrees after TDC. To much timing will hurt power just as much as too little.

Back when cars had distributors and springs/weights/vacuum controlled the advance curve the engineers didn't have the CAD tools to design and model engine designs that are available today. Quite often you couldn't establish the ideal advance curve because of poor combustion chamber design and inconsistent manufacturing so they established safe limits. This allowed the enthusiast to tune for their needs and make a significant improvement.

Today designs are very well optimized before the first piece of metal is machined and there is much less room for improvement.

A muscle car era bug block mopar needs upwards of 40 degrees of advance to make max power. The current generation Hemi, LS or Mod Motor makes max power with less than 30 degrees of advance and runs to much higher rpms.
 

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If lower grade fuel causes knock and retard timing how can it be better to use that fuel?
There is much more to fuel than octane. Different brands use different additives, such as detergents, lubricants, surface protectants, etc. 'Top Tier' brands use much more cleaning agents than required by law, and they will keep the engine running better, longer.

Thus, using a good (e.g., 'Top Tier') 87 octane fuel is better than using a crappy (e.g., oxidized, off-season, no-additives) 93 octane.

You are incorrect in your statement about causing knock. The Focus' engine does not knock when using 87 octane because it adjusts the timing. Of course, it is not getting as much power as it could get with a higher octane fuel, but that is of small importance compared to the cleanliness and life of the engine.
 

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So you're saying premium gas won't advance the spark curve for better low end power?
No it won't. It might keep it from being retarded but it won't advance it beyond what the engine was tuned for. Plus an engine needs less timing advance at low RPMs than at high RPMs. The engine needs the most timing advance at light load cruising when the throttle is barely open. Under this condition the cylinder does not fill with air/fuel efficiently so the spark has to happen sooner to ensure max cylinder pressure occurs at the approx 20 degrees ATDC i mentioned previously.

In the old days distributors had mechanical advance that was strickly rpm dependent, more rpms, more advance. They also had vacuum advance that added more timing in high manifold vacuum conditions such as light load cruising.
 

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I guess most people are not aware that all gas (in the area you live) is created equal. This is because for each area of the country their is only one refinery making the gas. This is especially true during the Summer, due to the EPA requiring at least 18 different formulations for at least 18 different parts of the country. Twice a year all refineries shut down for about 2 weeks so they can reformulate per EPA rules.

Here in Florida almost all of our gas comes from one refinery in the Gulf coast. Now the only difference between brands is that when the gas is moved from the refinery to storage tanks Shell, Mobil or whatever brand can then add additional additives if they want to. Otherwise all the gas (regular, Plus and Premium) has the same cleaning additives that the EPA requires. Also the Refinery only makes Regular and Premium. Plus is made by just blending Regular with Premium either at the retailers storage tanks or at the gas station.
 

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I guess most people are not aware that all gas (in the area you live) is created equal. This is because for each area of the country their is only one refinery making the gas. This is especially true during the Summer, due to the EPA requiring at least 18 different formulations for at least 18 different parts of the country. Twice a year all refineries shut down for about 2 weeks so they can reformulate per EPA rules.

Here in Florida almost all of our gas comes from one refinery in the Gulf coast. Now the only difference between brands is that when the gas is moved from the refinery to storage tanks Shell, Mobil or whatever brand can then add additional additives if they want to. Otherwise all the gas (regular, Plus and Premium) has the same cleaning additives that the EPA requires. Also the Refinery only makes Regular and Premium. Plus is made by just blending Regular with Premium either at the retailers storage tanks or at the gas station.
We have 22 refineries here in California. I ran one tank of premium through, and, although I thought is smoothed out my tranny's slight start-from-stop shudder, I didn't notice a difference in anything else - but I don't flog it anyway. I'm back to regular and I don't even notice any difference in the shifting.[sleep]
 
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