Octane levels result in different levels of performance on a stock

[paynecasey]

I searched the forums here with no direct answer but all seam in favor that the higher the octane you use the cars computer will recognize and change parameters resulting in a little bit more power. Apparently this is true for 03/04 Cobra's and 5.0 Mustangs. Is this true for all cars? Even though that are factory set to allow 87 octane?

Example 2014 Ford Taurus 3.5L Ti-VCT V6 with 288 hp and 254 torque has an 87 octane minimum requirement but says nothing about 91 being preferred like it does for the turbo engine options. With that being said would putting 93 octane result in more power, better throttle response and possible better fuel economy?

So in theory with 93 octane the Taurus could have 295+ hp (give or take) and 360+ lb feet of torque?


If you scourer the internet, Cars.com, consumer reports will all say your throwing your money away but for some reason I think they are full of crap.

I recently watched an episode of 5th gear where the took a car that made around 240 hp and connected its fuel line out of the car into buckets of gas outside the car. Each bucket had different fuels from different vendors ranging from the best to the cheapest. Oddly enough the cheap gas gave the weakest hp and the premium fuel gave almost 10 more hp.

Whats your thoughts? Do you buy 93 octane on your vehicles that are rated for 87?

 

[Coiled03]

Octane does NOT boost power. Gasoline contains the exact same amount of potential energy per unit volume no matter the octane number. The fact that it allows you to advance timing, and in some cases increase power as a result of that, is just taking advantage of the characteristics of the fuel. But the amount of energy available hasn't changed.

 

[xXGadfly09Xx]

Octane does NOT boost power. Gasoline contains the exact same amount of potential energy per unit volume no matter the octane number. The fact that it allows you to advance timing, and in some cases increase power as a result of that, is just taking advantage of the characteristics of the fuel. But the amount of energy available hasn't changed.

This

OP take a college level chem course

 

[paynecasey]

This

OP take a college level chem course

Went to college for an accounting degree. Only Chemistry I received was in high school.

 

[Dbzguy]

I havnt owned a car that didnt require premium in over 15 years so I'm no help to OP question

 

[thomas91169]

Octane does NOT boost power. Gasoline contains the exact same amount of potential energy per unit volume no matter the octane number. The fact that it allows you to advance timing, and in some cases increase power as a result of that, is just taking advantage of the characteristics of the fuel. But the amount of energy available hasn't changed.

This.

Vehicles nowadays can detect the octane rating of the fuel and add timing (or retard) if necessary. They also have knock detectors that can be used to detect knock and the ecu will advance timing until knock is detected.

 

[Mach828]

You have to have an engine that can benefit from additional timing. Many cars won't benefit because either the tunes max timing can be easily achieved with regular unleaded (ecu doesn't detect detonation and isn't pulling timing), or some motors just don't really respond well to a lot of timing advance. The largest gains from additional octane fuels are vehicles that must run really low timing to not experience any detonation (boost, heat, and compression are the primary factors).

 

[ElscottHavoc]

Here's something I wonder.
Here in Iowa, Super Unleaded has always been subsidized due to ethanol blending. The additional ethanol bumped up the octane to 89, but the subsidization made it 10 cents cheaper than 87. So 89 was cheapest, 87 was middle and 91 was highest for most stations. Some stations, such as Wal-Mart must have done further ethanol blending because they offered 89, 91, 93 with 91 being cheapest and they also typically beat competitors by 10 cents. Essentially, unless you specifically needed regular unleaded non ethanol blend, 89 was the way to go for most cars.

Recently, Iowa (and perhaps Nebraska) started requiring all unleaded gasoline to be ethanol blended. Now, when you pull up to the pumps, most stations have both super unleaded and regular unleaded at 87 octane, but super unleaded remains 10 cents cheaper.

My assumption is to be the same exact octane rating, they must share the same ethanol blend...otherwise, if one had more ethanol it'd be slightly higher octane - correct? Yet, there still remains a price difference between the two...so what's the difference now that would cause two equal octane ratings to necessitate separate pumps and prices?

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[Mach828]

^^

The ethanol and octane blends are done at the refinery. The vast majority of stations only have two gas tanks. One for your regular unleaded and one for the premium. Any midgrade options are blended at the pump from a combination of the two tanks.

 

[ElscottHavoc]

I see. I didn't know there were only two tanks. But then I'm still confused. So, say a local station here in Iowa offers:
87 Octane Regular Unleaded - $3.49
87 Octane Super Unleaded - $3.39
91 Octane Premium Unleaded - $3.59

Why is the Super Unleaded still 10 cents cheaper? My assumption is based that it deals with the ethanol subsidization still, yet they share the same blend and have the same octane rating. From the surface, besides price, super and regular appear identical.

And if you were to blend 91 with the 87, wouldn't you still get an 89? Yet, they still claim both regular and super as 87.

Or maybe I need to do further research and perhaps some 87 octane without the blend has not been phased out yet, but I could of sworn enough time has passed and that I've seen them both marked as ethanol blended - was in 2013 this was enacted.

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[esqeddy]

Octane is simply a measure of how much compression the fuel can withstand before it detonates on its own. It is not the measure of energy that a given fuel will produce.

You don't want the fuel/air mixture, which has been compressed into the combustion chamber to ignite before you hit it with a spark from the spark plug. If the octane is too low for the level of compression, that is what happens. This can damage the engine. Further, pre-ignition of the fuel will reduce the power output of the engine at the very least.

 

[jason6488]

So first of all
Octane is a fuel, like butane. It has a certain laboratory resistance to detonation. Gasoline is compared to octane and thats where the number system comes from. I don't remember the actual equation but it's not very complicated, can be looked up if you're that interested and I think is listed on the pump sometimes.
Second, I'm no expert on gas station tanks, but I do know MOST have 2 tanks, like mach828 stated. They probably do this for economical reasons. It's possible however that the particular station you mention has 3, or more tanks and is simply catering to customers who want fuel with or without ethanol. A few stations still offer ethanol free gas for a variety of reasons and maybe your station just wants to cover all the bases? Either way, to chime in with EVERYONE else here, a car tuned for 87 octane doesn't make any extra power on 91 or 93 or whatever else you have. I will say on a technical note I think higher octane fuels have very, very, very slightly less power per unit of fuel because of the additives blended to allow the higher rating, but I might be wrong. It's been a while since I read about octane ratings and such.

 

[black92]

Let me add a related question -

Vehicles that are E-85 capable, can they benefit from increased octane before running straight E-85? The reason I ask is because in the owners manual, my wife's 2010 Milan Premier 3.0 V6 is rated 240hp with 87 octane and 250hp with E-85. I would say it's possible it would pick up some power if I ran 89 or 91, but not enough to even notice and more likely be wasting money.

 

[ElscottHavoc]

Second, I'm no expert on gas station tanks, but I do know MOST have 2 tanks, like mach828 stated. They probably do this for economical reasons. It's possible however that the particular station you mention has 3, or more tanks and is simply catering to customers who want fuel with or without ethanol. A few stations still offer ethanol free gas for a variety of reasons and maybe your station just wants to cover all the bases? .

The only problem with that is that here in Iowa and also Nebraska, all unleaded fuel must be ethanol blended. Somehow, gas stations are offering two versions of 87 octane both blended with ethanol for different prices at the same pump. Many of these also offer a 3rd option of 91.

This law of all unleaded fuel being blended was enacted last year so surely they should no longer have non ethanol blend available. This isn't just one station either, its basically every station I've been to in Iowa.

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[bluestang41505]

Local 7 Eleven pump.

 

[wundrbird]

Everything below is based on what I've read in the past. Your mileage may vary:

I think that a car has to be able to sense octane changes with advanced knock sensors, as mentioned previously, to get any benefit by advancing timing. I know that my truck actually runs worse on octanes higher than 87. It will kick, buck, and sputter and the power is noticeably less. Lower octane fuels have more BTU's per gallon due to the fact that the additives in higher octane fuels actually lower total energy. The benefit, however, is that you can pump more 93 octane than 87 in a cylinder to make up for it's lack of energy due to its knock resistance.

And octane is an 8 carbon chain organic compound that is sometimes found in trace amounts in gasoline. Gasoline in its many different forms is compared to pure octane in its knock resistance. Pure octane (the chemical) is considered to be 100 octane (the rating of knock resistance). 93 octane fuel has 93% of the knock resistance of the pure chemical. Race fuels over 100 octane have more than 100%. Even race fuels have less total BTU's by volume than regular gasoline, but the knock resistance is so high that you can pump a LOT more fuel into the engine.

There are two ways to measure octane. There's an "R" method and an "M" method. (You can Google them for what they represent.) An average is taken and posted as the official octane rating. That's why you see (R+M)/2 on gas pumps.