Who uses premium gas in their 2v 4.6?

I use premium most of the time. I see a real, measurable benefit on longer drives, but it is not substantial enough to see in daily driving around town.

Here is a link to an article that discusses this very topic, and some of you might want to read it before making assumptions:
Regular or Premium? - Feature - Auto Reviews - Car and Driver

FWIW, the original article featured a pic of the vehicles in the test, and the Mustang was a GT, not a Cobra, IIRC. It is my understanding that the 2001 Cobra requires premium, and uses a knock sensor, while the GT calls for 87 and has no knock sensor (even if they think it does in the article). We know it's a GT because they don't say it requires premium, and it's an auto.

Anyway, my own experience jives with the article. I'm not arguing running premium is cost effective, but neither is driving a Mustang GT in the first place. But I would suggest those who claim there is no benefit or even a detriment should really consider the evidence and do their own experiments. Just saying there is no benefit based on faith alone is kind of silly.

95.0Stang said:

I went on a road trip...a 6 hour drive. I always use 91 octane and this would be no different. The first leg of the trip from Topeka to STL I got 27mpg, pretty good for a V8 car right? Then I filled up at a Mobil station in STL with 93 octane, really this was just to do it, I didnt expect any gains at all, but from STL to Indianapolis I got 30.2mpg which shocked the heck out of me! As I was leaving Indy I filled up with 92 octane which is the highest I could find around my hotel, and from Indy to STL I got 28mpg. Stopped at the same Mobil station in STL and filled up with 93 again, and the car did 30.1mpg back home to Topeka. This is MY experience, and why I just always use premium. I am sure there are variables, but honestly I thought these results were really great considering how my car is equiped. Ford said 26mpg HWY on the new car stcker for this car, so to beat that is impressive to me.
Current mods that COULD effect MPG...
1. O/R H-Pipe
2. Magnaflow Catback
3. Eibach Lowering springs( I figure aerodynamics may change and help)

Mods that SHOULD lower MPG
1. Heavier aftermarket Bullitt wheels
2. Heavier BFG tires in front
3. Heavier Goodyears to fit the 17x10.5 wheel in the back
4. Over 100 pounds of luggage in the trunk

Again this is purely my experience, and not based in science at all, just an FYI type thing!

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well when your cruising or on a road trip your in closed loop 99.9% of the time so the compy is constantly adjusting the timing to get the best fuel economy and power at the same time, so with the higher octane it can advance the timing farther and allow the better mileage.

me with 3.70's in the rear can still pull down about 260+ miles per tank driving in town with premium.

oxfordgt said:

This is a simple question to answer. If your not tuned for it then don't run it. Running 93 octane in a car tuned for 87 will cause carbon build up in the combustion chamber. Higher octane fuel burns slower which means that on a stock timing tune you will not burn all of the gas. This is what causes carbon build up and a loss i power.

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again think about closed loop. computer will advance the timing to the point of detonation. then pull it back a degree or 2. of course open loop higher octane will not benefit you unless you are tuned for it.

crazystang25 said:

again think about closed loop. computer will advance the timing to the point of detonation. then pull it back a degree or 2. of course open loop higher octane will not benefit you unless you are tuned for it.

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Except that it can't advance timing to the point of detonation and then pull it back because GTs don't have knock sensors so it has no way of knowing when detonation is occurring. It has take the air temp, air mass, water temp and the other variables it does know and calculate ignition timing based on the assumption you've got 87 in the tank.

Try this: Crank your base timing up a few degrees, then fill up with 87 and see if the computer starts pulling timing when it starts detonating or if it will happily lets your engine ping away in closed loop. Anybody who's had to stop at the next gas station to buy a couple of cans of octane boost when they accidentally filled up with 87 can tell you the answer.

The results 95.0Stang experienced are probably within the margin for error for Mustangs on the freeway, Prevailing winds could have helped him out on some legs, differences in elevation mean he's driving uphill on some legs and downhill on others, maybe he spent more time driving around one city than another. A single rest stop or break for lunch can have a huge difference on highway mileage, in my own experience, as can a slow down for traffic or construction.

Those are awesome results but too small a sample size to be compelling to me. Neither is the C&D article - 2 HP difference on a chassis dyno? That's less than one percent! They even admit in the article that that's well within the variability of testing. 0.3 in the quarter mile is more impressive but that's also an even more uncontrolled testing environment.

When I got over 30 MPG, that was back when the car was completely stock (except for mufflers) so it had either 87 or 89 in it

i have always run 93 octane in mine since i bought it. i bought my car used, bone stock. from day one it pinged and knocked, i thought maybe they had got bad fuel. it was low anyway so i filled it up on 87. was fine just driving around normally, but at wot it would knock pretty bad. i burned that tank out and put 93 in it, no more knock, been running 93 ever since. of course now i have mods and the car is tuned for 93. but even bone stock i couldnt get away with running 87.

i do not have a tune therefore its 87 fo me..

i run 93, but i have a tune for it. If i put 87 in it i will detonate like crazy.

patman0911 said:

The results 95.0Stang experienced are probably within the margin for error for Mustangs on the freeway, Prevailing winds could have helped him out on some legs, differences in elevation mean he's driving uphill on some legs and downhill on others, maybe he spent more time driving around one city than another. A single rest stop or break for lunch can have a huge difference on highway mileage, in my own experience, as can a slow down for traffic or construction.

Those are awesome results but too small a sample size to be compelling to me. Neither is the C&D article - 2 HP difference on a chassis dyno? That's less than one percent! They even admit in the article that that's well within the variability of testing. 0.3 in the quarter mile is more impressive but that's also an even more uncontrolled testing environment.

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Consider that 95.0Stang isn't the only one to see positive results. I used to take 800 mile round trips a few times a year, and decided to see if higher octane gave me better mileage. The conclusion was a definitive yes, IMHO. It's only a few mpg, but it was consistent and reliable. We're talking about filling up and driving on the freeway with cruise control until the next fill-up, and the mpg benefits were observed every time. In addition, the engine seemed to run smoother. And when you spend 10 hours at highway speed, you notice those things. I'm not saying the case is the same with every car, but I've got no doubts higher octane gives me better mileage and my engine runs better on it. As they say, YMMV

Given the lack of contrary evidence, I'm satisfied my results are NOT an aberration or the result of poor observation. The fact that an improvement can be measured would seem to imply that a very real benefit exists. All that's left is for you to test it yourself in conditions that you deem valid. I'm confident, given a fair test, that anyone with a 1999-2004 Mustang GT would see a benefit to running premium.

Also consider that some ping is considered "normal" apparently. The owner's manual to my 93 Celica stated that clearly. Now assume you have "some ping" with 87 octane, but Ford designed the engine to tolerate that mild amount. Fill up with higher octane and eliminate that ping, and you will see a slight increase in power and waste less gas in normal driving. And your engine will thank you

40oz said:

Consider that 95.0Stang isn't the only one to see positive results. I used to take 800 mile round trips a few times a year, and decided to see if higher octane gave me better mileage. The conclusion was a definitive yes, IMHO. It's only a few mpg, but it was consistent and reliable. We're talking about filling up and driving on the freeway with cruise control until the next fill-up, and the mpg benefits were observed every time. In addition, the engine seemed to run smoother. And when you spend 10 hours at highway speed, you notice those things. I'm not saying the case is the same with every car, but I've got no doubts higher octane gives me better mileage and my engine runs better on it. As they say, YMMV

Given the lack of contrary evidence, I'm satisfied my results are NOT an aberration or the result of poor observation. The fact that an improvement can be measured would seem to imply that a very real benefit exists. All that's left is for you to test it yourself in conditions that you deem valid. I'm confident, given a fair test, that anyone with a 1999-2004 Mustang GT would see a benefit to running premium.

Also consider that some ping is considered "normal" apparently. The owner's manual to my 93 Celica stated that clearly. Now assume you have "some ping" with 87 octane, but Ford designed the engine to tolerate that mild amount. Fill up with higher octane and eliminate that ping, and you will see a slight increase in power and waste less gas in normal driving. And your engine will thank you

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LOL that all made me laugh. 93 octane is not a more powerfull fuel then 87 octane so how are you claiming a power improvement? You might have felt a better running engine but more then likely it was just in your head trying to justify the extra cash you just spent to fill up. But if you did feel it run smoother then that means your engine is tired and was detonating alot (you can't always hear detonation). Run some seafoam thru your engine and I'll bet it smokes for an hour due to the carbon build up.

oxfordgt said:

LOL that all made me laugh. 93 octane is not a more powerfull fuel then 87 octane so how are you claiming a power improvement? You might have felt a better running engine but more then likely it was just in your head trying to justify the extra cash you just spent to fill up. But if you did feel it run smoother then that means your engine is tired and was detonating alot (you can't always hear detonation). Run some seafoam thru your engine and I'll bet it smokes for an hour due to the carbon build up.

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I am not going to claim a power improvement so much as a mpg improvement, and a smoother running engine. I ran seafoam through when I bought the car and again about a month ago, no real difference. I have owned the car for the last 13,000 miles(16 months). I have run premium(91 or 92 octane in Kansas) since I bought the car so it doesnt affect my wallet at all to fill up on premium as I am used to it. My engine is far from tired with 62,000 miles on it and no trips to the track yet. During my trip to Indianapolis the car ran down the highway better with the 93 than even the 91. I have to say that to me there really seams to be a difference. It may very well be in my head, but then the mpg data kind of backs me up. I felt a difference before I knew the mpg...For me I will continue to pay and extra $2/tank to have safety in mind for this spring when I get a tune for 91 octane.

Ateup said:

How many miles do you have on your car while running premium? Do you think that there could be a carbon build up issue over time even though it appears to run better now?

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I don't know, why would there be carbon build-up?

I've put ~50K miles on this one, the other I put ~40K on when I had it. Think about it - 50,000 miles and no issues on one engine alone. A combined 90,000 miles. How many miles would it take for something to show up that you'd believe to be related? How many miles would have to be driven with no issues to demonstrate there is no harm in using gasoline 4 frikkin' points higher on octane rating? I'm pretty sure if such a thing were to cause catastrophic damage, it'd have happened by now.

oxfordgt said:

LOL that all made me laugh. 93 octane is not a more powerfull fuel then 87 octane so how are you claiming a power improvement? You might have felt a better running engine but more then likely it was just in your head trying to justify the extra cash you just spent to fill up. But if you did feel it run smoother then that means your engine is tired and was detonating alot (you can't always hear detonation). Run some seafoam thru your engine and I'll bet it smokes for an hour due to the carbon build up.

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Learn to read.

See, if you could read, you'd see that I was suggesting that, never mind. You can't read anyway. And stop drinking seafoam.

40oz said:

Learn to read.

See, if you could read, you'd see that I was suggesting that, never mind. You can't read anyway. And stop drinking seafoam.

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I can read and the fact that you are claiming better gas mileage and power improvement just shows that you know nothing about what a higher octane gasoline is. It is not a more powerfull or explosive gas. It's not a better cleaner gas. The higher octane only means that it burns slower which is more resistant to detonation. A slower burn means that not all the gas is being burned in the combustion chamber leading to carbon build up in a stock timing engine. With the gas not being burned in the chamber that means your mixture is rich and you are getting less power. This is not like a normal rich condition where the o2's will see it and the computer will adjust. The raw gas is expelled into the exhaust and and burned in the header. This causes the o2 sensor to read lean which makes the computer add fuel leading to power decrease and mpg decrease. There is no way to gain mpg or hp by running 93 octane without a tune.

WARNING: FRIKKIN' NOVEL AHEAD!

oxfordgt said:

I can read and the fact that you are claiming better gas mileage and power improvement just shows that you know nothing about what a higher octane gasoline is. It is not a more powerfull or explosive gas. It's not a better cleaner gas. The higher octane only means that it burns slower which is more resistant to detonation. A slower burn means that not all the gas is being burned in the combustion chamber leading to carbon build up in a stock timing engine. With the gas not being burned in the chamber that means your mixture is rich and you are getting less power. This is not like a normal rich condition where the o2's will see it and the computer will adjust. The raw gas is expelled into the exhaust and and burned in the header. This causes the o2 sensor to read lean which makes the computer add fuel leading to power decrease and mpg decrease. There is no way to gain mpg or hp by running 93 octane without a tune.

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OK, see, I and other people have observed the same thing. We observe "reality," which trumps theory. If I was in your shoes I'd dispute our claims as well. But real-world testing is the observation of the physical world. No reputable scientist worthy of the label would argue with real-world observation. That's the cornerstone of the scientific method - form a theory, deesign an experiment to test the theory, execute the experiment, observe the results, and amend the theory to match the real-world observed results. Theory falls before reality. Whenever reality differs from theory, theory is wrong, NOT reality.

Most sources I find say higher octane doesn't burn significantly slower, it just ignites later under pressure and heat. In other words, it takes more pressure/heat to make it combust. A spark will ignite it the same as lower octane. Even if it burns slower, it's such a minor difference in the time it takes the flame front to advance it is a moot point. Most N/A engines only burn for the top 90* of crank travel regardless of octane requirement. It's all burned before the exhaust valve opens either way.

And let's just say you are right, it takes so much longer to burn. Therefore the crank travels farther around while the fuel is burning as a consequence. That just means more power is generated. As fuel burns it pushes the piston and crank farther around the circle. Once the all the fuel is burned, the resulting gasses start to cool and stop pushing on the piston. The farther you can push the piston during combustion the more power you make. F/I engines ideally push the piston down past 90*, that's how they make more power on the same displacement. You can't burn more gas in the same amount of time with the same size cylinder. It takes longer to combine more O2 and gasoline, so it pushes the piston farther around the circle and hence transmits more power to the crank. You just provided a valid theory on why higher octane gas makes more power - by burning slower

In addition, consider that a fast-moving flame front compresses the unburnt mixture in front of it, giving rise to the possibility of pre-combustion that may or may not be noticed in the midst of a combustion event, but wastes power. A slower-moving front gives less chance for this condition to develop and higher octane fuel makes this more unlikely, and therefore less power is wasted from pre-ignition during lower rpms, such as are encountered during cross-country travel. High-rpm operation gives little opportunity for knock or pre-ignition (in front of the spark-ignited flame front) so differences in octane due to knock or pre-ignition would be less noticeable.

I'm not endorsing the idea that higher octane burns slower, merely showing that if it did, the effects would be entirely beneficial. I don't know if it does, I just know my results of real-world testing.

In Minnesota (where I live) the only non-oxygenated gas is 93 octane. Oxygenated gas has less energy content than non-oxygenated, so mileage and horsepower WILL be higher with non-oxy gas. Oxygenated gas at first seems to be a benefit to power since the fuel is delivered along with a portion of O2, but mileage suffers because you are paying for a portion of a gallon of oxygen for each gallon of fuel. Non-oxygenated gas is "all fuel" and all the O2 is provided by the atmosphere, so you see higher mpg numbers. Power should not suffer during closed-loop where the O2 sensors have input, but during open-loop where fuel is dumped in according to a stoichiometric number, it probably doesn't assume a portion of the "fuel" is O2. So if open-loop operation at the factory assumes non-oxy fuel and you run oxygenated fuel, the engine actually delivers less fuel than the factory planned for and power output suffers. It's not that high octane contains more energy bacause of the octane number, it's that non-oxygenated fuel contains more energy and 93 octane is almost always non-oxy in MN.

Given that, a person in Minnesota buying non-oxygenated gas will see a mpg benefit over oxygenated gas, and a benefit at the dyno most likely. The extra cost for non-oxygenated fuel here means there is no monetary savings, but the mileage and power benefits are real.

Look, give it a try under conditions you consider valid. That's all you can do. You're not a fool, so you can come up with a valid test. It's called physics, the observation of the physical world.

I've done it and am convinced. You would be too if you just gave it a shot. I know higher octane isn't magic and doesn't contain more power just because it has higher number somewhere. I am unable to explain my results scientifically and unassailably, but that's because I observed them in a practical application with nothing to prove. I had as much motivation to see higher octane as a waste of money, but that wasn't what I found. I've stated before that I doubt it's a cost-effective way to spend your money, so it's not like I'm justifying the extra cost. It just happens that in my car higher octane results in real-world benefits.

Regarding higher octane burning slower, I refer to these pages (without endorsing them across-the-board - too much "garage science" and not enough "lab science"):

"The antiknock ability is related to the "autoignition temperature" of the hydrocarbons. Antiknock ability is _not_ substantially related to:

---The energy content of fuel, this should be obvious, as oxygenates have lower energy contents, but high octanes.

---The flame speed of the conventionally ignited mixture, this should be evident from the similarities of the two reference hydrocarbons. Although flame speed does play a minor part, there are many other factors that are far more important. (such as compression ratio, stoichiometry, combustion chamber shape, chemical structure of the fuel, presence of antiknock additives, number and position of spark plugs, turbulence etc.) Flame speed does not correlate with octane. "

from IMOC Articles - Octane ratings, fuels and water injection

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"A lot of people also confuse octane with flame-front propagation speed which is yet another independent factor. Take the old-days measurement of octane-ratings with iso-octane (2,2,4-trimethylpentane) with a octane-100 rating and n-heptane with a 0-octane rating. They both have the exact same flame-front speed, yet one of them has a fairly high anti-knock index. The other, n-heptane, has such low knock-resistance that you can just tap the beaker and the stuff would explode!"

from Octane Rating - Thor Racing (Japanese Performance Car Tuning)

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Flame speed - Wikipedia, the free encyclopedia

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Your questioning of what I've found makes me question it. Yet the more I test it and the more I research it, the more convinced I am that my findings are not BS or wishful thinking. Believe me, if I could find a way to convince myself that cheap gas was as "good" as high octane, I'd be down with it. But at the end of the day, it seems you get what you pay for whether that was the original idea or not.

i used to, then i ran out of money. 87 runs perfectly fine in my car, which is what is recommended

I run 93 octane in my car only because I'm still running my Steeda timing adjuster. The car had pinging at low rpm's with the 89, so ive been running 93 since the install. There is no advantage of going with 93 octane aside from spark timing changes, forced induction, etc.