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Old 04-20-2011, 08:48 AM   #1
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Default 87 vs 91 octane

Any time there's an increase in gas prices you'll often see news stories posing the question: "Is premium fuel worth the premium price?" After the "expert" gives his two cents, the reporter will often conclude thus: "There you have it-if your vehicle runs fine on regular, stop throwing your money away on premium!" The average consumer can easily be lulled to the conclusion that there are no benefits whatsoever from running gasoline that costs a premium price of 20 cents more per gallon. The logic experts use to justify their claims is straightforward: If you run 87 octane and your car doesn't knock or ping, you'll see no difference if you use 89 or 91 octane. There are also claims that if your vehicle is only designed to run on 87 octane, you could possibly encounter problems from using higher octane.
To test the "premium gasoline is a waste of money" theory, we borrowed an unmodified Jetta 2.5L designed to run on 87 octane. In order to get a more accurate read on performance and pick up on any drivability differences, we decided to do more than just dyno tests. We performed the various tests using four tanks of gasoline. Under real-world driving conditions, the tank was run from full to empty first on 87, then on 91, and then back to 87. With the last remnants of 87 the car was dynoed until completely empty, then refilled with 91 and dynoed again.


Vehicle Data
Engine: 2.5-liter I5, dohc, 20-valve
Transmission: Six-speed automatic
Mileage: 4,520
Current modifications: None Dyno Type:
Six-speed automatic
Baseline : 87 octane
Performance
Temperature: 66 F
Humidity:15% Peak Power: 133 hp @ 5976 rpm
Peak Torque: 134 lb-ft @ 3444 rpm

Test Notes
All testing was performed on the same day. All horsepower and torque numbers are quoted at the wheels. Keep in mind that the properly calibrated "Mustang" dyno produces more accurate real world numbers. While these numbers might seem low when compared to figures gathered from a Dynojet, what is important is the differences between each dyno run. When we strapped the Jetta to the dyno the needle of the fuel gauge was right at the red marks and we dynode until the fuel light appeared. All five of the Jetta's 87 octane runs were virtually identical with no major variations and at no time did the vehicle experience any knocking or pinging.


Graph 1: Baseline 87 Octane...

read full caption



Graph 1: Baseline 87 Octane vs. 91 Octane

Test 1
Performance
Peak power: 138 hp @ 5908 rpm
Peak torque: 146 lb-ft @ 4060 rpm
Peak power gain: 7 hp @ 5790 rpm
Peak torque gain: 13 lb-ft @ 4150 rpm
Temperature: 67 F
Humidity: 13%
Pros
Increase of 1-2 mpg
Increased throttle response and smoother power transitions
Reduce risk of knocking or pinging
Reduce risk of horsepower loss from heat soak

Cons
$0.20 per gallon price premium

Test Notes
We took the Jetta to a gas station about a mile away from the dyno facility and filled it up with 13.74 gallons of 91 octane gasoline. We then drove the vehicle for 25 miles to give the vehicle a chance to adapt to the octane increase and make sure there was no 87 octane left in the lines.
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Old 04-20-2011, 08:50 AM   #2
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Conclusion
Does higher octane fuel makeadifference on all vehicles? It did in this case. Because of VW's advanced electronics and highly adaptive engine management, the Jetta 2.5L has an elastic response to a changes in octane levels. Once we put in the 87 octane, we could feel the drop in performance-less responsive, less peppy, and overall just different. The engine instantly detected the reduced octane levels and adapted for standard performance. This analysis was based on more than 1,200 miles of driving over a week.
Switching between the two octanes allowed us to use the dyno to detect and confirm or refute any driving subtleties we noticed during the week. Even though the Jetta's gas tank flap advises 87 octane, the dyno graphs clearly show that running premium gasoline does have performance benefits including, a slight increase in fueleconomy. In the end, you get what you pay for. If you want standard performance use standard gasoline. But if you want premium performance, pay for premium gas.

COSTS SUMMARY
91 OCTANE FUEL: .20/GALLON AVERAGE PREMIUM $.20

Last edited by Deathscythe40; 04-20-2011 at 08:52 AM. Reason: error
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Old 04-20-2011, 03:26 PM   #3
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thumbs up! I think the 91 octane is definetly worth the premium, but that could just be me
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Old 04-20-2011, 04:20 PM   #4
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I'm sure someone will disagree with this statement, but I put in 91 on my TC and I think it makes a lot of difference, feels better, feel as if it has more power, and the engine idles a bit softer...

Funny thing is that the above, per experience is true based on my 2 Nissan Sentras SE-R. I have a regular auto SE-R and a SE-R Spec V.

Both use premium gas per the recomendations in the owners manual, and trust me, if you put anything less than that, the car feel as if its going to die and blow up; it shakes, it sounds awful, it has no power. To agree further more, the SE-R 2.5 motor is the same as the altima, but you can put 87 in an altima but not in the SE-R, as stated above the computer system plays a big part to adapt to decrease/increase performace in relation to the garbage we throw in the gas tank...I'm no expert but from experience, I agree with the above statement. I'll rather pay 20 cents more a gallon and feel confortable and to get 87 and have my cars feel like crap.

Thanks for the write up!
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Old 04-20-2011, 04:28 PM   #5
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Just go by what the manual says.
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Old 04-20-2011, 04:43 PM   #6
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Quote:
Originally Posted by Cisco_TeamShogun View Post
I'm sure someone will disagree with this statement, but I put in 91 on my TC and I think it makes a lot of difference, feels better, feel as if it has more power, and the engine idles a bit softer...

Funny thing is that the above, per experience is true based on my 2 Nissan Sentras SE-R. I have a regular auto SE-R and a SE-R Spec V.

Both use premium gas per the recomendations in the owners manual, and trust me, if you put anything less than that, the car feel as if its going to die and blow up; it shakes, it sounds awful, it has no power. To agree further more, the SE-R 2.5 motor is the same as the altima, but you can put 87 in an altima but not in the SE-R, as stated above the computer system plays a big part to adapt to decrease/increase performace in relation to the garbage we throw in the gas tank...I'm no expert but from experience, I agree with the above statement. I'll rather pay 20 cents more a gallon and feel confortable and to get 87 and have my cars feel like crap.

Thanks for the write up!
i feel the same way,,even though people tell me using premium on my scion is a waste,i still use it,cause car feels more alive i dont have to clean the injectors as often,overall feels alot more responsive,unlike 87 where it wasnr as good
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Old 04-20-2011, 05:36 PM   #7
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Edit: nvm. Click on the graph to see results.
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Old 04-20-2011, 08:24 PM   #8
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This data is irrelevant to the tC. You can't extrapolate results from one car and apply them to all cars, including the tC.

Also 87 octane is no more or less "dirty" than 91/93 octane. Saying you "don't have to clean the injectors as often" is complete nonsense.

Lastly, if you look at the power curves, you can see that for the VW 2.5L, all the gains were at the high-end of the rev-range, and actually included a loss of low-end torque. I don't know about you guys, but I'm not constantly flogging my engine, and even if the tC could gain power overall (which has yet to be proven), if the result of premium fuel were in any way similar to that of the VW there would be no gains when putting around town. The horsepower curves didn't diverge until ~3650 RPM and torque wasn't consistently greater until 3500 RPM in the picture above.
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Old 04-21-2011, 07:20 PM   #9
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Quote:
Originally Posted by VVTinme View Post
This data is irrelevant to the tC. You can't extrapolate results from one car and apply them to all cars, including the tC.

Also 87 octane is no more or less "dirty" than 91/93 octane. Saying you "don't have to clean the injectors as often" is complete nonsense.



Lastly, if you look at the power curves, you can see that for the VW 2.5L, all the gains were at the high-end of the rev-range, and actually included a loss of low-end torque. I don't know about you guys, but I'm not constantly flogging my engine, and even if the tC could gain power overall (which has yet to be proven), if the result of premium fuel were in any way similar to that of the VW there would be no gains when putting around town. The horsepower curves didn't diverge until ~3650 RPM and torque wasn't consistently greater until 3500 RPM in the picture above.
as they say....use premium to achieve the maximum performance of the vehicle,rather its true or not..i know for a fact i dont have to clean my injectors as often as i did with regular maybe mine are shot..overall by me premium is 50 cents more..why not use it..the car reacts to it alot better then regular..but yea all cars are different....i just responded to the other person that mention using premium in his scion
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Old 04-21-2011, 10:35 PM   #10
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Quote:
Originally Posted by VVTinme View Post
This data is irrelevant to the tC. You can't extrapolate results from one car and apply them to all cars, including the tC.

Also 87 octane is no more or less "dirty" than 91/93 octane. Saying you "don't have to clean the injectors as often" is complete nonsense.

Lastly, if you look at the power curves, you can see that for the VW 2.5L, all the gains were at the high-end of the rev-range, and actually included a loss of low-end torque. I don't know about you guys, but I'm not constantly flogging my engine, and even if the tC could gain power overall (which has yet to be proven), if the result of premium fuel were in any way similar to that of the VW there would be no gains when putting around town. The horsepower curves didn't diverge until ~3650 RPM and torque wasn't consistently greater until 3500 RPM in the picture above.
Octane should make little difference to everyday driving, but if you want a bit more, I am a believer that higher octane helps. Combustion temps are different, for better or worse, which may explain why ppl feel that a change in octane helps. Again, depending on how you drive, periodic induction/injector cleaning is necessary, to alleviate carbon buildup. True the same detergents are in all grades, but exhaust temp is used for minute timing adjustments, and octane affects that. This is the power that some claim to feel, while others say nothing's changed.
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Old 04-24-2011, 12:51 PM   #11
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Quote:
Originally Posted by jnaval View Post
Just go by what the manual says.
You haven't read the manual, have you?

I have.

I could be mistaken, but I believe the manual said to use at least 87 octane. It did not say to ONLY use 87 octane.

I think 91 octane could be better at times, but I've never seen a noticeable difference. The gas mileage did not seem to increase a noticeable amount. However, the price after filling the tank was noticeable.

To conclude: It is not worth it to me to fill up with premium. Just don't get the cheap Arco stuff. Use Shell or Chevron/76.
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Old 04-24-2011, 09:59 PM   #12
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Quote:
Originally Posted by kvnhmmd View Post
You haven't read the manual, have you?

I have.

I could be mistaken, but I believe the manual said to use at least 87 octane. It did not say to ONLY use 87 octane.

I think 91 octane could be better at times, but I've never seen a noticeable difference. The gas mileage did not seem to increase a noticeable amount. However, the price after filling the tank was noticeable.

To conclude: It is not worth it to me to fill up with premium. Just don't get the cheap Arco stuff. Use Shell or Chevron/76.
I didn't say anything about using only 87 and I didn't condemn using other than 87. IIRC, the manual says something like 87 recommended, research 91. Besides, I have an xB2, our manuals probably differ. I posted what I posted just to state that instead of speculating all of these "performance benefits" to using higher octane, to just go by what the manual says.
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Old 04-25-2011, 12:33 AM   #13
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Originally Posted by jnaval View Post
I didn't say anything about using only 87 and I didn't condemn using other than 87. IIRC, the manual says something like 87 recommended, research 91. Besides, I have an xB2, our manuals probably differ. I posted what I posted just to state that instead of speculating all of these "performance benefits" to using higher octane, to just go by what the manual says.
I understood that you were suggesting to use 87. I also agree that 87 is more logical. You are correct, the 2011 tC owners manual also says "87 recommended, research 91" (at least it sounds very familiar, I don't feel like going out to the car and digging up the manual)

But that manual does not say to ONLY use 87, so I doubt there will be any problems with using higher octane. The only difference might be 1-2 more MPG or so, and a few horse power, which would only be noticeable on the Dyno, and your wallet. Pick which one is more important.

For daily driving - 87 octane
For the track - 91 or higher; if it really works.

I doubt the possibility of increased gas mileage is worth the extra .10-.20 cents more per gallon.

But it's your car, and the options are there, so pick what you want.
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Old 04-25-2011, 12:39 AM   #14
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Octane ratings are always specified as a minimum because all that octane means is resistance to detonation. Any car that takes 87 can run on 91/93. It is not indicative of any potential gains (or lack thereof) from a higher octane.
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Old 04-25-2011, 02:13 AM   #15
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Originally Posted by Deathscythe40 View Post
Conclusion
Does higher octane fuel makeadifference on all vehicles? It did in this case. Because of VW's advanced electronics and highly adaptive engine management, the Jetta 2.5L has an elastic response to a changes in octane levels. Once we put in the 87 octane, we could feel the drop in performance-less responsive, less peppy, and overall just different. The engine instantly detected the reduced octane levels and adapted for standard performance. This analysis was based on more than 1,200 miles of driving over a week.
Switching between the two octanes allowed us to use the dyno to detect and confirm or refute any driving subtleties we noticed during the week. Even though the Jetta's gas tank flap advises 87 octane, the dyno graphs clearly show that running premium gasoline does have performance benefits including, a slight increase in fueleconomy. In the end, you get what you pay for. If you want standard performance use standard gasoline. But if you want premium performance, pay for premium gas.

COSTS SUMMARY
91 OCTANE FUEL: .20/GALLON AVERAGE PREMIUM $.20

Cool story bro, now do this for the tc2.
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Old 04-25-2011, 02:44 AM   #16
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I have a TC2 now but before all I had were Hondas wich have high compression
Hondas DOHC VTEC engines are all over 10 compression or even higher
and says 91 only or higher okey whats point the rule of thumb always has been if your compression is 10 and higher like the TC2 which uses the AR engine which is 10.4:1 use 91 now the car has 14.5 gallon fuel tank I live la so 91 about $4.50 and 87 about $4.30 87 is $62.35 and 91 is $65.25 to fill up the tank difference $2.9 you could come come up with excuses but cant afford $3 extra a tank a energy drinks cost the same old TC1 guys could argue this because of their compression 2az-fe 9.6:1 its up to you here some facts
The compression ratio of an internal-combustion engine or external combustion engine is a value that represents the ratio of the volume of its combustion chamber from its largest capacity to its smallest capacity. It is a fundamental specification for many common combustion engines.
In a piston engine it is the ratio between the volume of the cylinder and combustion chamber when the piston is at the bottom of its stroke, and the volume of the combustion chamber when the piston is at the top of its stroke.[1]
Picture a cylinder and its combustion chamber with the piston at the bottom of its stroke containing 1000 cc of air (900 cc in the cylinder plus 100 cc in the combustion chamber). When the piston has moved up to the top of its stroke inside the cylinder, and the remaining volume inside the head or combustion chamber has been reduced to 100 cc, then the compression ratio would be proportionally described as 1000:100, or with fractional reduction, a 10:1 compression ratio.
A high compression ratio is desirable because it allows an engine to extract more mechanical energy from a given mass of air-fuel mixture due to its higher thermal efficiency.[citation needed] High ratios place the available oxygen and fuel molecules into a reduced space along with the adiabatic heat of compression–causing better mixing and evaporation of the fuel droplets.[citation needed] Thus they allow increased power at the moment of ignition and the extraction of more useful work from that power by expanding the hot gas to a greater degree.[citation needed]
Higher compression ratios will however make gasoline engines subject to engine knocking if lower octane-rated fuel is used, also known as detonation. This can reduce efficiency or damage the engine if knock sensors are not present to retard the timing. However, knock sensors have been a requirement of the OBD-II specification used in 1996 model year vehicles and newer.

In other words use higher octane to reduce Knock and better A/F Ratios unless you want to be Cheap Cheap Cheap

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Old 04-25-2011, 06:12 AM   #17
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<snip>

In other words use higher octane to reduce Knock and better A/F Ratios unless you want to be Cheap Cheap Cheap
The tC doesn't knock on 87.

Octane has nothing to do with A/F ratios, either. Cars that can utilize higher-octane fuel (such as flex-fuel vehicles) will advance the ignition timing.
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Old 04-25-2011, 06:53 AM   #18
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The tC doesn't knock on 87.

Octane has nothing to do with A/F ratios, either. Cars that can utilize higher-octane fuel (such as flex-fuel vehicles) will advance the ignition timing.
I never said the engine knocks the owners manual says you can use 87 but it also states research was done on 91 now why they conduct their tests higher octane I tell you why go to the first thread Reduce risk of knocking or pinging key word reduce not eliminate

Detonation can be prevented by any or all of the following techniques: the use of a fuel with high octane rating, which increases the combustion temperature of the fuel and reduces the proclivity to detonate; enriching the fuel/air ratio, which adds extra fuel to the mixture and increases the cooling effect when the fuel vaporizes in the cylinder; reducing peak cylinder pressure by increasing the engine revolutions
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Old 04-25-2011, 06:56 AM   #19
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Originally Posted by Deathscythe40 View Post
I never said the engine knocks the owners manual says you can use 87 but it also states research was done on 91 now why they conduct their tests higher octane I tell you why go to the first thread Reduce risk of knocking or pinging key word reduce not eliminate

Detonation can be prevented by any or all of the following techniques: the use of a fuel with high octane rating, which increases the combustion temperature of the fuel and reduces the proclivity to detonate; enriching the fuel/air ratio, which adds extra fuel to the mixture and increases the cooling effect when the fuel vaporizes in the cylinder; reducing peak cylinder pressure by increasing the engine revolutions
There's no risk of detonation running 87.
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Old 04-25-2011, 01:54 PM   #20
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heres the deal...ive seen lots of threads aguring over regular vs premium,i say put in what you want,its your car and your $$$$$...end of story,rather you feel a difference or not....you know your car and what you experience...
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