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Old 06-29-2001, 12:10 PM   #1
The Reverend
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Default gasoline type

I tried the search but 'gas' was too short of a word. So with that said, what is the best type of gasoline to use in 2.5. The manual says 87 but I was wondering if that was recommended by everyone here.
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Old 06-29-2001, 12:16 PM   #2
Longshot
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The manual is correct, 87 octane is all you should need for a 2.5RS, ppl will probbly argue that 92 octane is better so it must be better for the car, but it does little to boost performance unlike earlier model cars.

The best way to go is to get the swampgas 87 for daily use then fill it up with 91 and some octane booster on track days, make sure you reset the ECU if you decide to do that.

This is all just basedon my opinion and what I've read from this board and other websites. I'm sure someone else will argue how you should use 104 chevron or sumthin...

Korey
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Old 06-29-2001, 12:25 PM   #3
The Reverend
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Thanks for the info. That is pretty much what I was thinking but I wanted to hear someone echo it back.
Later,
The Rev
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Old 06-29-2001, 02:20 PM   #4
wcbjr
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I agree that a higher octane than 87 is preferred. But if I go, let's say, a month on 87 then switch to 93, I get a dramatic loss of power at first. Anybody explain this?
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Old 06-29-2001, 07:54 PM   #5
inpreza kid
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a higher octane rating would help only if you advance your timing somehow to take advantage of it. i personally put the 92 in my car. i guess its just personally preference.
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Old 06-29-2001, 08:04 PM   #6
Boom
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I have tried all the gas octanes, and to be totally honest the 91 is the best. I really do feel a difference in the car. I have ping with 87 through the first 1000 RPM's and I have ping with 89 if I start off from a stop without giving it enough gas. With the 91 I have never heard pinging. Just some FYI I have an intake, and exhaust on a 99 RS. Plus I autox as much as I can, so I try to keep the good stuff in there, just so I don't blow up the engine or anything. Just my opinions, it may not be the same for you. Try them all, you really have nothing to lose except a few bucks.
Steve
99 White RS
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Old 06-30-2001, 08:09 AM   #7
LUME
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I have never experienced any problems with 89. At low engine speed and high load, I have experienced ping with 87. Start as low as you can go and move up gradually. As soon as you hear ping under NORMAL driving conditions, you know you've got to bump it up a notch. If you tow a lot, then go with something above 90....

--RD
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Old 06-30-2001, 10:23 AM   #8
ylexot
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Use 87 unless you get pinging. Octane is a gasoline additive that makes gas less flamable. It also decreases the energy in the gas. In other words, <b>you get less power!</B>

Why use higher octanes? If the compression ratio is high enough or the car is run long and hard, there is a chance of premature detonation of the fuel (not good). Octane helps prevent that. So Imprea Kid is correct. If you advance the timing, there is a greater chance of premature detonation and a higher octane should be used.

Micah
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Old 06-30-2001, 02:57 PM   #9
IBO
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What if I have my throttble body bored, intake, and exhaust, would I need to switch to 89 or 92(I am currently using 87)??

Also, since higher octane gas give less power output, does that mean if I use somethin' like 89 or 92 will give me a smother ride??
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Old 06-30-2001, 03:35 PM   #10
e_a_olson
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I have no problems with Mobil regular (87) in my MY02 RS. Why bother paying for Super if it's not going to be a noticable difference?
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Old 06-30-2001, 04:09 PM   #11
Rubr_Duky
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Through my own in-precise research, and self funded experiments.....


My typical day of driving included over 100 miles of freeways both with and without traffic, and a little bit of mild street driving.

I filled up with 87 octane, and put 13.2 gallons in. I drove like a sane person for an entire tank. Resut: 243.4 miles.
Filled up with 87 again, and drove like a mad-man. Result: 203.8 miles.

I then switched to 89 octane, and performed the same rituals after having put 12.7 gallons of 89 in: Sane: 310 miles, Mad Man: 289 miles.

Filled up with 92 and ran out all of the low octane stuff. same thing: Sane: 401 Mad Man: 320.

You do the math, and with the price of gas now starting to come back down, have a little fun. I've also noticed that with the A/C on, I typically run through about 1/3 more gas, and a little less in bumper to bumper traffic.


RD

Optimum speed with A/C: 70
Optimum speed without A/C: 75.

I once got 420 miles on a tank with 92, and the cruise control set at 85.
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Old 07-01-2001, 03:23 PM   #12
imprezadan
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I only use 92 octane. It really only costs a little more per tank(you're not filling up a suburban) and I swear that it makes a big difference. The earlier Imprezas are so ping sensitive that it only makes sense to spend the extra $2.
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Old 07-02-2001, 01:35 AM   #13
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Quote:
Octane is a gasoline additive that makes gas less flamable. It also decreases the energy in the gas. In other words, you get less power!
I do not believe this is true. Octane is a molecule of 8 Carbons and 18 Hydrogens bonded together. If you have a higher amount of Octane then you'll have more Hydrogens to burn. So Hydrogen = More Power It may make it less flamable but it makes it more combustable.

If I am wrong please correct me,

Chris
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Old 07-02-2001, 08:02 AM   #14
ylexot
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MGXsport - Truthfully, I don't know since I'm not the chemist in the family However, going by that logic, water would be explosive (one oxygen, two hydrogens). The problem is that the energy required to rip the hydrogen from the oxygen (or carbon in the case of octane) is quite large.

IBO - good question about mods. Unfortunately, my answer is that I don't know. Since I'm getting an intake from Cobb, maybe they'll answer the question for me if I ask.
As for smoother ride, I wouldn't think different octanes would make a difference you could feel.

Rubr_Duky - your data is illogical. You need to say how many gallons were required to re-fill the tank after X miles. Saying how many gallons before driving proves nothing. Hypothetical example: I fill up with 15 gallons, drive 400 miles, then it takes 10 gallons to fill the tank. What's my MPG? 40 (400 miles/10 gallons). I'll have to try this experiment some time. I know that right now I get ~25 MPG (and I always drive like a madman )

Micah (why yes, I <B>am</B> a rocket scientist)
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