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  #13  
Old 12-10-2012, 02:01 PM
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Re: Pentastar octane

Just curious how do you guys even know which grade has ethanol and which doesn't? Here in Chicagoland area pumps say nothing more than "may contain 10% ethanol" and nothing more.
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  #14  
Old 12-10-2012, 02:30 PM
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Re: Pentastar octane

The ones that have Ethanol say it may contain 10%, there is normally a sign on the one that doesn't or a sticker that says "Ethanol Free".
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  #15  
Old 12-10-2012, 03:13 PM
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Re: Pentastar octane

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Originally Posted by JTS97Z28 View Post
Just curious how do you guys even know which grade has ethanol and which doesn't? Here in Chicagoland area pumps say nothing more than "may contain 10% ethanol" and nothing more.
I think the labeling requirements vary by State. Mine says "up to 10%" on all three grades and not much else. There are some gas stations that advertise none, but I think that is just for the premium grade.
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Old 12-10-2012, 07:14 PM
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Re: Pentastar octane

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Originally Posted by tuned8e View Post
According to what? A butt dyno?.. more than likely the 'pep' is all in your head hate to tell you.

In fact it was a "butt dyno".
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  #17  
Old 12-10-2012, 09:18 PM
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Re: Pentastar octane

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Originally Posted by scooterha View Post
In fact it was a "butt dyno".
... thank you for confirming this scientific octane analysis

ha ha
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  #18  
Old 12-10-2012, 11:35 PM
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Re: Pentastar octane

Owners manual says the engine is rated for 87 Octane. I have absolutely no problem putting in 87. Better than premium with my old STi :/
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Old 12-11-2012, 05:13 AM
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Re: Pentastar octane

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Originally Posted by tuned8e View Post
... thank you for confirming this scientific octane analysis

ha ha
Anytime
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  #20  
Old 12-11-2012, 10:36 AM
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Re: Pentastar octane

OK please repeat after me: octane has nothing to do with power (btu/lb). Octane is simply a measure of how fast it burns.

Now a problem with SI (spark ignition) engines is burn time: how long it takes from spark to maximum chamber pressure which you want to reach at somewhere between 7 and 12 degrees ATDC. Everything about the driving experience (power, accelleration, MPG) depends on how close to that "sweet spot" you can stay.

Higher octane means slower burning gas means you need more timing advance to hit that spot (lots of other things like chamber filling vary requirements). Being flex-fuel, the Pentastar can problably handle up to 103 octane so 89 is not a problem, but does it do any good ? Probably not but would take a dyno to tell.

For other reasons (like $$$) most people want to run the lowest octane possible and you might as well. It is possible that higher octane will result in a slightly smoother idle, a bit of variance is typical when right on the edge, why many maps go a little rich at idle.

GM had what was called a Standard Test 20 when dynoing engines. It was popularly known as "Maximum Power and Detonation" because you reach maximum power for any regeme on the edge of detonation. Hard part is not going over the edge since every engine is slightly different.

If you really care about theory may I suggest Sir Harry's "The High Speed Internal Combustion Engine".

ps "up to 10%" can be read as "at least 9%".
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  #21  
Old 12-11-2012, 03:43 PM
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Re: Pentastar octane

89 in my Overland (2012) and my late 2008 gives me the best combination of performance and mileage. Just got a 2013 Overland and have yet to fill it from dealer. But I'll go to 89 based on past experience.
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Old 12-11-2012, 03:44 PM
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Re: Pentastar octane

All grades in Chicago area are 10% ethanol. In other words, rubbish to make the farm lobby happy.
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  #23  
Old 12-11-2012, 09:49 PM
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Re: Pentastar octane

Not all bad, true MPG goes down but I've seen indications that engines run cleaner and cooler on 10%.
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  #24  
Old 12-12-2012, 05:16 AM
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Re: Pentastar octane

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Originally Posted by Todd VanSlyke View Post
All grades in Chicago area are 10% ethanol. In other words, rubbish to make the farm lobby happy.
We used to pay farmers to grow nothing.
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