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Hi, everyone. I just bought my '12 Mk3 sedan 3 days ago. Looking at engine specs, I see that it says 12:1 compression ratio.

My car didn't come with the Owner's Manual. Do I need to run premium unleaded due to the high compression?

TIA
 

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No. It will run fine on regular unleaded.
 

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Focus Preacher
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Well, the thread I referenced is already a sticky - just in the performance section for the MkIII engine....
 

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Discussion Starter #8
Why not a big Sticky FAQ regarding every questions that are always asked at the top of the forum ???
Well, the thread I referenced is already a sticky - just in the performance section for the MkIII engine....
Thank you very much for the link. I didn't think octane rating for stock engines would be in the performance forum.
 

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Not to start a debate, but running Premium will improve fuel economy and give a little more power (prevents the timing from being retarded). Is is worth the extra money? You will need to decide that. I run premium because I have a heavy foot.
 

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just my 2 cents. i filled my tank up for $25 bucks today using 92 octane premium. lets be real, that's cheap. why not use it? i've ran it in my car since day 1 and will always run it in this car.
 

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Sonic's Mk3 Crew #17
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I typically use 89 but with how crazy cheap our gas prices are these days I threw in 91 this week, the highest we can get around here. Why not?
 

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I typically use 89 but with how crazy cheap our gas prices are these days I threw in 91 this week, the highest we can get around here. Why not?
Using higher octane rating on a car that is not tuned for it will not produce any gains in either performance or fuel economy, so if you use higher octanes, it is a personal choice and there is nothing wrong with that. Using top tier rated fuels such as Chevron or Shell will produce benefits, not in immediate performance and fuel economy, but in keeping carbon build up down, a real concern on direct injection engines such as those on our Foci.
 

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Premium here in VA is currently ~$0.6>regular...hardly a bargain. Yes..I realize that absolute dollars spent now for a tank of premium are in-line with what we were paying for a tank of regular a few months ago but why not pocket the savings? For me, I fill up 2-3 times a week so this is ~$15 more a week to run premium to commute ~500 miles a week with (no real benefit that I can tell) but I suppose if I was driving more normal amounts it wouldn't be a big deal. I have been thinking that I will try to only run Top-Tier gas from now on as it doesn't cost me anymore money but I get more cleaning agents.
 

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Using higher octane rating on a car that is not tuned for it will not produce any gains in either performance or fuel economy, so if you use higher octanes, it is a personal choice and there is nothing wrong with that. Using top tier rated fuels such as Chevron or Shell will produce benefits, not in immediate performance and fuel economy, but in keeping carbon build up down, a real concern on direct injection engines such as those on our Foci.
I will respectfully disagree with your first sentence. I'm sure this has been beaten to death on this forum, but having knowledge of fuel injection systems gives me some insight into how they function.
In an advanced GDI system, there is typically spark advance control through knock sensors or anti-knock systems. This allows the computer to retard timing if detonation is present, or allow it to run fully advanced if no detonation is detected. Running 93 compared to 87 octane likely allows the computer to run fully advanced and the performance gains can be felt.
I would agree that, in most older non-direct injection systems, this advanced state of timing adjustment is not present and you would be wasting money running premium fuel if the system cannot adapt.
There can actually be a detriment to long term use of fuel that is of too high an octane, but that's a different discussion and does not apply to the newest Focus.

Not to start a debate, but running Premium will improve fuel economy and give a little more power (prevents the timing from being retarded). Is is worth the extra money? You will need to decide that. I run premium because I have a heavy foot.
I have found that using 93 octane vs. 87 octane yields nearly zero difference in fuel economy. However, there is a noticeable performance gain at partial throttle from about 1500-3500 rpm. I attribute this to the system not pulling as much timing out in this rev range with the higher octane fuel.
 

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Using top tier rated fuels such as Chevron or Shell will produce benefits, not in immediate performance and fuel economy, but in keeping carbon build up down, a real concern on direct injection engines such as those on our Foci.
In a conventional port injected engine that would be true. In a direct injected engine, the fuel is injected directly into the combustion chamber and the fuel doesn't wash over the intake valves. Top tier fuel is still beneficial for the combustion chamber.
 

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Using higher octane rating on a car that is not tuned for it will not produce any gains in either performance or fuel economy, so if you use higher octanes, it is a personal choice and there is nothing wrong with that.
Negative. We're talking about a direct injection engine with a 12:1 CR and twin independent variable cam timing.
 

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Interesting bit below. Its not just a standard motor that retards timinig to "slum" it on regular..its a different beast. Do you honestly think that if Ford could squeeze better performance/economy out it by using premium they wouldn't recommend it? (Maybe I should have said "Do you think Ford would purposely design a motor that runs inefficiently on regular and then recommend that as the fuel type?")

"A couple of key technologies allow us to do that, and one is direct injection," said GM's Davis. "One of its big benefits is it provides a cooling of the of the intake charge in the engine. That cooling suppresses the autoignition reactions that lead to knock. In a sense, by adding direct injection you can lower the octane requirement of the engine. The other contributor to knock is the combustion process itself. By a careful design of the combustion system geometry, the shape of the combustion chamber, as well as the airflow characteristics and the flame propagation, you can actually make the combustion system more tolerant of the lower octane fuels."

At the end of the day, I don't care what fuel folks run, but I think the premium bit is a bit placebo..but maybe I am wrong. I have tried it multiple times and not noticed any real difference whether on the highway or around town (performance or mpg). Dyno results would be interesting and may tell a different story. Yes..I realize the 2012 manual says that you can get increased performance running premium but its not in there now and I think this is b/c it was a mistake/carry-over from the ST manual. Again, just my opinion.
 

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I have found that using 93 octane vs. 87 octane yields nearly zero difference in fuel economy. ...
That's a point I've been wondering about. I know a few have claimed increased distance / fuel quantity unit on > 87 octane, but if it's truly so, couldn't Ford advertise the crap out of that?

The fueleconomy.gov site shows the Focus at 26/27 to 36/37 miles per gallon on 87 octane fuel. And I'll leave it to others to determine how the EPA determines which gasoline octane rating to use on particular vehicles, but nonetheless, if the highway mileage could go from 37 to 39 or 40 by simply switching to premium fill, wouldn't someone at Ford be marketing this to the maximum?

Couldn't Ford request the EPA to test the Focus (non-ST of course) on premium fuel? Or does the EPA say "tough shit", we're testing your Focus on regular, and we don't care if it gets better mileage on premium? (side note: the Mustang GT 5.0l V8 is also tested on regular fuel - I find that odd).
 
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