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Old 07-28-2008, 10:50 AM   #1 (permalink)
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87 octane vs 89 octane

To be honest, I'm not a gear head, I'm a computer nerd. From what I'm told this is pretty straight forward, I just want to make sure thats the case.

I recently (a day after I joined the forum) filled up all but about 3 L of my tank with 89 octane. I've been told that depending on the car, it can make a big or small difference. so far, Ive gone through roughly 34L of my tank and I am at 400 KM, making it 8.4 L/100KM (27 MPG) which is WAY better than my previous 13 L/100KM (18 MPG). So far it looks to be worth it.

Would you guys say that generally 89 octane gives substantially better results? Is it worth the money filling up on it every time? Or do most of you guys use 87?


Note: this gas is also rated to be up to 10% ethanol.

yeah i know its a noobie question but hey, you gota start somewhere.

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Old 07-28-2008, 11:37 AM   #2 (permalink)
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I would say to stick with what your car was built for, as timing and all that is optimized for a certain octane.
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Old 07-28-2008, 11:56 AM   #3 (permalink)
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Quote:
Originally Posted by SVOboy View Post
I would say to stick with what your car was built for, as timing and all that is optimized for a certain octane.
Can it have adverse affects if you use it consistently? I did notice that in drive I go faster with no throttle...
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Old 07-28-2008, 12:02 PM   #4 (permalink)
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I don't think it would have adverse effects, but most people who use a different octance will report lower FE...then again, every car is different.
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Old 07-28-2008, 12:23 PM   #5 (permalink)
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Quote:
Originally Posted by SVOboy View Post
I don't think it would have adverse effects, but most people who use a different octance will report lower FE...then again, every car is different.
Lower FE than 87? Or lower FE per cost?

Looking at Wikipedia for Fuel injection etc, it looks to be fairly safe since the engine would compensate (according to Fuel Injection). As for belts and such (of which I don't know much about), I don't imagine anything really would change, its all very static.

I seem to be getting some great numbers from this gas though, and the performance is clearly different (albeit still crappy ).
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Old 07-28-2008, 12:23 PM   #6 (permalink)
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I've always used the lowest octane that my car used w/o knocking. In some cars that meant regular driving through Indiana and premium in Vest Virginia. I never noticed a chang in mpg that couldn't be attributed to terrain and/or traffic. But if it is getting you better FE I say use it until the tank before your e-check if you have one.
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Old 07-28-2008, 12:37 PM   #7 (permalink)
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Quote:
Originally Posted by kill-9 View Post
I recently (a day after I joined the forum) filled up all but about 3 L of my tank with 89 octane. I've been told that depending on the car, it can make a big or small difference. so far, Ive gone through roughly 34L of my tank and I am at 400 KM, making it 8.4 L/100KM (27 MPG) which is WAY better than my previous 13 L/100KM (18 MPG). So far it looks to be worth it.
Don't make conclusion by filing one tank only. You get better FE, not ONLY because of switching octane. Maybe you drive on different routes, at different speed, in different mood or that pump fills your tank more than the others(so you can go further). Try at least 3 tanks. If you get 50%+ FE consistently, then keep using 89. Maybe you should try 91 later for even better FE. But, for my car, getting 40mpg with 87 makes me happy already. I don't expect it will get 60mpg by switching to 89 or 91.
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Old 07-28-2008, 02:08 PM   #8 (permalink)
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Quote:
I've always used the lowest octane that my car used w/o knocking. In some cars that meant regular driving through Indiana and premium in Vest Virginia. I never noticed a chang in mpg that couldn't be attributed to terrain and/or traffic. But if it is getting you better FE I say use it until the tank before your e-check if you have one.
I agree that it could be attributed to terrain but my route doesn't really change.
Quote:
Originally Posted by xbUser View Post
Don't make conclusion by filing one tank only. You get better FE, not ONLY because of switching octane. Maybe you drive on different routes, at different speed, in different mood or that pump fills your tank more than the others(so you can go further). Try at least 3 tanks. If you get 50%+ FE consistently, then keep using 89. Maybe you should try 91 later for even better FE. But, for my car, getting 40mpg with 87 makes me happy already. I don't expect it will get 60mpg by switching to 89 or 91.
Yeah I will definatly be continuing the experiment. The plan was 2 thanks 89, 2 thanks 87. But I've measured my milage before and really only get around 10-12 L / 100 KM regularly. This is why its odd to have such a dip in consuption, and the only change really seems to be the octane.

I will test it however .

Quote:
Originally Posted by BlackDeuceCoupe View Post
Heh!

And yet another opinion (this time my own)...

I run a high-compression, high-performance, 8200 RPM red line engine in my hypermiler. The manufacturer clearly states that this engine REQUIRES premium unleaded fuel, both in the owner's manual, and gas tank door on the donor car.

I run 87 octane...

Having said that, look at my mileage below - in the graphic!

I have run both premium and regular unleaded in this car - flea market gas and Top Tier...

Regular unleaded Top Tier gas (Shell, Chevron, Texaco etc) runs better in my ride than super unleaded non-Top Tier gas - undoubtedly because of the additives! You can do the same thing by dumping Chevron Techron (for instance) down your tank at every fill - but why bother? Gas prices are the same everywhere you go - in this market - so why spend extra on the additives, you know?

Anyway, my car starts better on regular unleaded (less cranking), runs better (more power) - but unfortunately gets identical mileage (shrug).

In my considered opinion, the only place you're going to notice a difference with higher octane gas is at startup and WFO (full-throttle)!

You're certainly NOT going to notice a difference in mileage - unless you got some underlying mechanical problem that makes your motor knock under low load and partial throttle.

In that case, fix the PROBLEM! Don't use a crutch...
But is it really a problem? A friend of mine had a 92 Acura, and it wanted 89. When he did run on 87, his efficiency went down (not noticable) but he said it was more worth it to go with 89. And again, a friend of mine with the exact same car who drives alot noticed this as well. They dont measure as closely as you guys of course.

I buy the cheapest gas around because I know as well as the next guy that its all the same dead dinosaurs, and I was even skeptical about this higher octane (I bought it cause it was on sale, it is every thursday night). I just find it odd that I show such a drastic increase with just 1 tank. I was even kinda heavy on the pedal since I had more accelerating than usual to do.

EDIT: And just an add, my engine does seem to kick a bit less than when I used 87 (and i've never used 89 before). The difference in performance as well was only in the lower end of the spectrum, I still need about 2.5k revs to keep it at 60 mph.
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Old 07-28-2008, 02:20 PM   #9 (permalink)
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The octane ratings on the pump are minimum ratings. It's possible that if they are mixed with 10% ethanol, the 87 and 89 are both about 91 anyway. The change in mpg is almost definitely due to something else.
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Old 07-28-2008, 02:26 PM   #10 (permalink)
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Quote:
Originally Posted by jesse.rizzo View Post
The octane ratings on the pump are minimum ratings. It's possible that if they are mixed with 10% ethanol, the 87 and 89 are both about 91 anyway. The change in mpg is almost definitely due to something else.
I guess we'll see once I fill up again.

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