Highway milage with 87 octane vs. 91 octane fuel [Archive] - GrandAmGT.com Forum

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john_ertw
06-28-2004, 12:03 PM
I've read the posts that say there is no benefit to using high octane fuel if it's not called for, but that has not always been my experience.

I'm wondering if anyone has any experimental data that says a grand am with the 3.4L engine gets better milage or the same milage with high octane fuel. I know that on my parents minivan, it gets better highway milage with super fuel and it is actually cheaper to use super than regular because of the increased range.

mshu7
06-28-2004, 01:30 PM
Please, don't start this topic AGAIN! This has been beaten to death. 87 octane is the recommended level in the manual.

If you've searched through every single thread on this website and you can't find the answer then you probably won't find it by starting a new thread. Just live with the gas mileage that you get with 87.

Hexx
06-28-2004, 01:35 PM
Search search search...don't gimme any "I searched but found nothing." Just put in "gas mileage."

If you run lower (83 is it?) you will be fine. I ran this while the gas prices went up. I am now back to running mid grade. Running higher octane is pointless unless you have the mods to utilize it (which most everyone's car here doesn't need).

Running 91 on a stock GA is like running 108 (at most raceways) in our car. IT DOES NOTHING. Burns cleaner that is for sure, and I hear it is good if you are running some type of nitro/alkohol injection.

IBTL :boogie:

Kdawg207
06-28-2004, 01:38 PM
:banghead

dcb2001gt
07-11-2004, 10:23 AM
I usually run 50 octane not 83. Do they even make that?????????? :vomit:

Irate
07-11-2004, 10:46 AM
running anything over 87 w/ a stock computer is useless. The computer is not programmed to recognize octane past 87.

john_ertw
07-11-2004, 07:55 PM
I wasn't going to bring this topic up again due to everyone's attitude to my initial post, but for those who care, I have used super gas for the past 2 and a half weeks and have noticed better milage than with regular gas on the highway. I don't think I've run enough tanks to have an accurate report yet, but I noticed that my milage is better by about 2L/100km with the super gas. Now keep in mind that this is doing 95% highway miles. I ran one tank of 94 octane (with 10% ethenol) and one tank with 91 octane (no ethenol). The non-ethenol tank did a bit better than the ethenol enhanced tank. Keep in mind I don't think two tanks is enough to compare. I'll report back when I feel that my findings are conclusive.

Craig99SE2
07-11-2004, 08:37 PM
FYI - With Ethanol gas like Sunoco, the Real Octane index is 2 less than the RM/2 on average than pure petro gas. So your Sunoco 94 is equivalent to 92 petro.

As for the rest of it ... it has been beaten to death. It's prolly a fluke as the PCM is adjusting fuel trim. Once the PCM settles (~200 miles), it will probably go back to normal.

rocketfast123
07-12-2004, 09:30 AM
83 the lowest i seen is 87 :wtf

Irate
07-12-2004, 10:15 AM
87 is the standard in the country. I don't think they'll allow lower unless you go to a specialty place.

There's really nothing to debate here. If you think you got better mileage w/ higher octane, then it was a fluke. You may have been driving more conservatively, maybe less head wind. There are too many variables, and too much evidence supporting no benefit from higher octane on an 87-programmed computer.

Feel free to spend more if you want. If you think your car does better w/ 93, then all the more power to you. :thumbs:

Slim
07-12-2004, 10:33 AM
Just thought I'd throw in my $0.02. Even if your car is getting better gas mileage, it's not better enough to justify the price. Sunoco 94 is about 12 - 15 cents more per litre than regular 87. Our tanks our 53 litres, so figure 48 for your average fill from empty. Figuring 15 cents/ litre, is your car getting $7.20 more mileage out of the tank of 94? Probably not, so stick to 87.

Actually, I'll do the math for you. :)

You said it's about 2L/100k better. Average GA owner gets about 450kms per tank. So that means, on average, you're getting 9 litres more mileage out of a tank than the average. That works out to (figure $0.75 per litre) $6.75. Based on that, it's costing you $0.45 to fill up with premium.

Hexx
07-12-2004, 11:19 AM
87, 89, & 92 are the octanes here....my bad. Dont know why I was thinking 83.

Anyways...I will let you guys know....that on a FULL tank I got 360miles....that was on 89. I drove from Maine to Mass (outside of boston) and back home again (visited my grandfather).

I will fill up with 92 this weekend and see what I get (even though I have my CAI to install now so that will make a difference...)....I'm going about the same distance this weekend (NH at my bros place).

Whatever works for you guys, do it...no need to argue.

atc3434
07-12-2004, 01:31 PM
Higher octane may not help mileage, but it sure as hell fights knock retard. And less KR equals more timing, which does infact equal more power. So if your car hits 0KR with 87, yup, its pointless... but if your normal like everybody else, you get some KR with 87, and maybe still a touch with 93. My two pennies. BTW Hexx, you'll see better mileage, because of the CAI, at least most people, including myself, have.

CoopGT
07-12-2004, 03:11 PM
Higher octane may not help mileage, but it sure as hell fights knock retard. And less KR equals more timing, which does infact equal more power. So if your car hits 0KR with 87, yup, its pointless... but if your normal like everybody else, you get some KR with 87, and maybe still a touch with 93. My two pennies. BTW Hexx, you'll see better mileage, because of the CAI, at least most people, including myself, have.

*iagree*

My Mileage went up nicely on long distance runs.

Craig99SE2
07-12-2004, 05:07 PM
Well yeah ... once you start modding it changes things ...

Greed4Speed
07-13-2004, 09:30 AM
We saw no increase with higher octane when my wife was putting 160 miles/day on her GA. No increase using synth oil either.

As for KR, if you're getting KR running 87 in the 3400 (which w/a low compression ratio is designed to run low octane) then you have some issues and running a higher octane is just masking them, or you're modded.

atc3434
07-13-2004, 01:22 PM
As for KR, if you're getting KR running 87 in the 3400 (which w/a low compression ratio is designed to run low octane) then you have some issues and running a higher octane is just masking them, or you're modded.

I think you'd be surprised to find that almost all GM V6's will experience some KR in stock trim with 87 grade gas. 3100's, 3400's, 3800's, all generations. You may never hear it spark knock, but autotap it, and I'll bet you'll find its pulling the timing some, especially when that motors good and hot. If your searching for maximum performance, especially in late night traffic light sprints, where the motor gets real warm, higher octane will help reduce KR, allowing more timing, and therefore better performance. As far as mileage goes, I don't think its worth the price.

john_ertw
07-13-2004, 07:20 PM
Just thought I'd throw in my $0.02. Even if your car is getting better gas mileage, it's not better enough to justify the price. Sunoco 94 is about 12 - 15 cents more per litre than regular 87. Our tanks our 53 litres, so figure 48 for your average fill from empty. Figuring 15 cents/ litre, is your car getting $7.20 more mileage out of the tank of 94? Probably not, so stick to 87.

Actually, I'll do the math for you. :)

You said it's about 2L/100k better. Average GA owner gets about 450kms per tank. So that means, on average, you're getting 9 litres more mileage out of a tank than the average. That works out to (figure $0.75 per litre) $6.75. Based on that, it's costing you $0.45 to fill up with premium.

Slim25, the difference is I've been getting about 600km on just less than 50L of super gas as opposed to the 450km you used in your math. That makes a difference and is why you say it's not worth it. Keep in mind I do 95% highway driving between 90 and 110km/hour and almost never go over 3000rpm (that's how I get the 600km/tank). Using your math, if you figure over 600km I save 12 litres (2L/100km - my number). Than take $0.75/L like you did and multiply it by 12L. That gives you $9. Which is more than the $7.20 you came up with.

I did the math too, but slightly different. Here's my calculations:

(x+y)/x = a/b
where x is the price of regular (cents/litre)
y is the difference between regular and super (in cents/litre)
b is your milage is km/L for regular gas
a is your milage in km/L for super gas.

a and b can be considered constants by doing a long enough run on each gas (I'd say at least a few thousand km's to get something that's acurate). y is usually constant (depending the gas station I've seen it vary by 10 cents/L upto 13cents/L). Solve for x. If the price of regular gas is less than what you got for x, then you're better off financially getting regular. If regular gas cost more than x, you are better off getting super gas.

Now let me put some numbers into this:

I'll use numbers that I have found from my experience over the past 2 months (these are actually conservative which make regular sound better than it is):
y=10 (from Canadian Tire which is what I use usually)
b=10 km/L (this is equivlant to 10L/100km)
a=11.5km/L (this is equivlant to 8.7L/100km)

Plug these in:

(x+10)/x = 11.5/10
(x+10)/x = 1.15
x+10 = 1.15x
10 = 0.15x
x = 66.7

This means gas has to be cheaper than 66.7cents/L for it to be better to use regular gas.

I don't want to argue with people. I just wanted to see if anyone else has had the same findings as I have. If you think you're better off on 87 octane, use it. If you think super gas is better, than go ahead.

On a side note, I think regular is the better deal if you do more city driving (stop and go).