Higher Octane Gas does....
03-12-2003, 09:38 PM
#1
Old School
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iTrader: (6)
Join Date: Jan 2001
Location: Union City
Posts: 14,983
Car Info: '99 RBP GM6
Higher Octane Gas does....
what to an RS?
I have a 1999 2.5 RS
Perrin Filter
Stromung Cat back
Ground wire Mod
I've ran 87 octane forever, and started using 89 for safety reasons, as i run the car hard, and wouldn't want it to ping, so a little extra protection there. First tank, car ran sluggish. 2nd tank, car ran ok. this is my third tank, and the car's revs have smoothed out a little, and the car pulls cleaner now.But the jumpy torque is gone.
Am I just imagining this? I was under the impression that the ECU wouldn't advance timing for higher octane gas. Is something else going on here?
The few times i've put in 91 for kicks, the car had become sluggish.
-Gagan
I have a 1999 2.5 RS
Perrin Filter
Stromung Cat back
Ground wire Mod
I've ran 87 octane forever, and started using 89 for safety reasons, as i run the car hard, and wouldn't want it to ping, so a little extra protection there. First tank, car ran sluggish. 2nd tank, car ran ok. this is my third tank, and the car's revs have smoothed out a little, and the car pulls cleaner now.But the jumpy torque is gone.
Am I just imagining this? I was under the impression that the ECU wouldn't advance timing for higher octane gas. Is something else going on here?
The few times i've put in 91 for kicks, the car had become sluggish.
-Gagan
03-12-2003, 10:55 PM
#2
Registered User
Join Date: Nov 2002
Location: Aiea, HI
Posts: 713
Car Info: 02 RS
for me i tired plus for a few fillups and then i tried premium for a few fill ups and all i noticed for milage and performance was nothing. just alittle less money in my pockets.
but that is only my opinion. i have an pdm intake, K&N filter, and a lightened pulley.
but that is only my opinion. i have an pdm intake, K&N filter, and a lightened pulley.
03-13-2003, 08:37 AM
#6
Old School
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Join Date: Jan 2001
Location: Union City
Posts: 14,983
Car Info: '99 RBP GM6
Originally posted by Scubaru
I too noticed sluggishness when I changed grades or fuel brands, it'll take about 2~3 tanks for your ECU to readjust to the new fuel-hence sluggy....
I too noticed sluggishness when I changed grades or fuel brands, it'll take about 2~3 tanks for your ECU to readjust to the new fuel-hence sluggy....
cool. I'm at that point. what did the ECU do?
-Gagan
03-13-2003, 09:43 AM
#7
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Posts: n/a
Well having a dyno at my disposal leads to testing some of the curiosities that have come to my mind such as different grades of gas.
On Texas gas and stock ECU I made the most power on 87 octane gas. On Texas gas with a Unichip and advanced timing I still surprisingly made more power on 87 than 89 or 91. Other factors were not allowing me to add more timing to take advantage of the higher grades of gas.
Now switch to Utah. With the same programming I had to run 91 octane with the ECU upgrade (didn’t get re-tuned once I moved) or I would get hesitations and an occasional detonation. I then removed the Unichip and ran stock ECU for header testing. Now I can run 87 with no problem. I guess the gas in Utah is pretty crummy or the re-tune on the Unichip was that important. I just never got the time.
On Texas gas and stock ECU I made the most power on 87 octane gas. On Texas gas with a Unichip and advanced timing I still surprisingly made more power on 87 than 89 or 91. Other factors were not allowing me to add more timing to take advantage of the higher grades of gas.
Now switch to Utah. With the same programming I had to run 91 octane with the ECU upgrade (didn’t get re-tuned once I moved) or I would get hesitations and an occasional detonation. I then removed the Unichip and ran stock ECU for header testing. Now I can run 87 with no problem. I guess the gas in Utah is pretty crummy or the re-tune on the Unichip was that important. I just never got the time.
03-14-2003, 08:30 PM
#9
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iTrader: (12)
Join Date: Nov 2002
Location: Reno, NV
Posts: 18,369
Car Info: 1993/2000/2001 GF4 mostly red
I switched to 91 the day I performed my Snorkelectomy, which was in December. I noticed a couple things. First, EJ25s have MASSIVE intake noise when you uncork them! Second, the car had a deeper exhaust note at idle and part throttle on the 91. Third, I am getting 1.5-2 mpg more by using 91. That means it's paying for itself, plus I get better knock protection.
I am hypothosizing that by switching grades and opening up the intake, I forced the car to run leaner without retarding timing, which seems to have had a slight effect on power and throttle response. I still shudder when I look up after adding 13 gallons, but I remind myself that I got 30-40 miles farther by paying an extra $3, plus the side benefits. I know it might be purely the placebo effect, but I feel like the switch is worth it.
Second, the car had a deeper exhaust note at idle and part throttle on the 91. Third, I am getting 1.5-2 mpg more by using 91. That means it's paying for itself, plus I get better knock protection.I am hypothosizing that by switching grades and opening up the intake, I forced the car to run leaner without retarding timing, which seems to have had a slight effect on power and throttle response. I still shudder when I look up after adding 13 gallons, but I remind myself that I got 30-40 miles farther by paying an extra $3, plus the side benefits. I know it might be purely the placebo effect, but I feel like the switch is worth it.
03-17-2003, 11:09 AM
#10
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Posts: n/a
Originally posted by scoobiejosh
Well having a dyno at my disposal leads to testing some of the curiosities that have come to my mind such as different grades of gas.
On Texas gas and stock ECU I made the most power on 87 octane gas. On Texas gas with a Unichip and advanced timing I still surprisingly made more power on 87 than 89 or 91. Other factors were not allowing me to add more timing to take advantage of the higher grades of gas.
Now switch to Utah. With the same programming I had to run 91 octane with the ECU upgrade (didn’t get re-tuned once I moved) or I would get hesitations and an occasional detonation. I then removed the Unichip and ran stock ECU for header testing. Now I can run 87 with no problem. I guess the gas in Utah is pretty crummy or the re-tune on the Unichip was that important. I just never got the time.
Well having a dyno at my disposal leads to testing some of the curiosities that have come to my mind such as different grades of gas.
On Texas gas and stock ECU I made the most power on 87 octane gas. On Texas gas with a Unichip and advanced timing I still surprisingly made more power on 87 than 89 or 91. Other factors were not allowing me to add more timing to take advantage of the higher grades of gas.
Now switch to Utah. With the same programming I had to run 91 octane with the ECU upgrade (didn’t get re-tuned once I moved) or I would get hesitations and an occasional detonation. I then removed the Unichip and ran stock ECU for header testing. Now I can run 87 with no problem. I guess the gas in Utah is pretty crummy or the re-tune on the Unichip was that important. I just never got the time.
God Bless the EPA. I have a buddy here in Delaware that recently moved back from San An and has a procharger on his Trans Am. He said the other day "the only thing going in my car is sunoco 94." He said that the **** we get here is exactly that. Probably cause the EPA makes us run this "oxygas" to help keep the emitions down, yeah, right.
03-18-2003, 05:07 PM
#11
Registered User
Join Date: Nov 2002
Posts: 56
Gains
There was a guy on the 'other' subaru board that wanted to know the same thing that some of you guys want to know. He tested 89 and 93 octane gas to see if any changes in the way the engine operates took place. He looked for changes on his PocketLogger.
What he had found out was that timing was more advanced with the higher octane gas than with the lower octane gas. As far as I can remember, no hp/torque gains or gas mileage was tested.
At any rate, he did find out that the Subaru ECU does make adjustments with a different grade of gas. If you have a factory service manual, you'll notice that on most Subarus (as far back as 1989) the ECU will adjust timing constantly to get the most advanced timing it can up to a point. I just don't know what the timing limit is.
I personally tested different octane gas at the dragstrip with an ECU reset. What I found out is that with both of my cars (1989 2.7ltr Subaru XT6 and 1997 2.2ltr Impreza), they both performed slightly worse with higher octane gas. Torque on the low end 'seemed' to be improved and the car got noticably more responsive on the low end.....especially right off idle. Even with higher 100+ octane gas on an N/A engine the car seemed even MORE responsive but 1/4 mile times got even slower still. I was familiar with the reasoning behind this but I had to find out for myself. *What's important to know about this is that even though the car was slower, the 1/4 mile time could've still come out the same due to the responsiveness increase of your off-idle. You would have to take advantage of this though with good tires and good traction (60ft times)*. The differences of the 1/4 mile times was within 2/10ths of a second but it was consistent.
You are encouraged to test this out to find out how different octanes perform on your own car since everyone's car doesn't react to a change the same way. Take Care!
What he had found out was that timing was more advanced with the higher octane gas than with the lower octane gas. As far as I can remember, no hp/torque gains or gas mileage was tested.
At any rate, he did find out that the Subaru ECU does make adjustments with a different grade of gas. If you have a factory service manual, you'll notice that on most Subarus (as far back as 1989) the ECU will adjust timing constantly to get the most advanced timing it can up to a point. I just don't know what the timing limit is.
I personally tested different octane gas at the dragstrip with an ECU reset. What I found out is that with both of my cars (1989 2.7ltr Subaru XT6 and 1997 2.2ltr Impreza), they both performed slightly worse with higher octane gas. Torque on the low end 'seemed' to be improved and the car got noticably more responsive on the low end.....especially right off idle. Even with higher 100+ octane gas on an N/A engine the car seemed even MORE responsive but 1/4 mile times got even slower still. I was familiar with the reasoning behind this but I had to find out for myself. *What's important to know about this is that even though the car was slower, the 1/4 mile time could've still come out the same due to the responsiveness increase of your off-idle. You would have to take advantage of this though with good tires and good traction (60ft times)*. The differences of the 1/4 mile times was within 2/10ths of a second but it was consistent.
You are encouraged to test this out to find out how different octanes perform on your own car since everyone's car doesn't react to a change the same way. Take Care!
Last edited by Myxalplyx; 03-18-2003 at 05:11 PM.
03-21-2003, 09:58 AM
#12
Guest
Posts: n/a
Use 87 octane. Higher octane in a car that doesn't need it can actually hurt your performance. Why? Well, unless you've increased your compression ratio or flow exponentially, there's no benefit to running higher octane fuel. High octane is more resistant to detonation. Translation: It's harder to burn. That could make it more difficult for the flame front to begin and can even slow down the flame front. That would result in a loss of power and, if the entire charge is not burned before the exhaust valves open, can result in an increase in pollution in the exhaust charge. Use the octane that your car is rated for. If the manual says 87 octane, then that's what you should be putting in there. An extremely effective intake/header/exhaust package might warrant 89 octane. Add an aggressive cam profile with heavy tuning and you might have to bump it up to 91 octane.
03-21-2003, 08:07 PM
#13
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Posts: n/a
i own a '93 impreza L and almost always have ran 93 and occasioanlly 89. i have even put in 94 (with no noticable differences in power or economy). lately since the hight gas prices, i have used 87. i don't notice any power loss and it seems that my milage has actually increased a bit. though that could be due to more money in my pocket.
03-25-2003, 04:44 PM
#14
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Join Date: Feb 2003
Location: Glen Rock, PA
Posts: 527
Car Info: 95 Impreza coup, green, 5speed 1.8l awd
87 octane might perform better but here in PA 87 octane at some gas stations is or at least seems to be cut with water or something that makes my 95 1.8L run bad. The only way to combat this is to buy 94 octane or 91 octane depending or where I buy at. But in other parts of the country this may not be a problem.
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