Premium gas Vs performance

I inadvertently put half a tank's worth of high octane gas in my Elantra recently. I normally use basic unleaded so I guess I wound up with an
octane somewhere in between. The odd thing was I seemed to notice the car having a bit more pickup afterward. I'm wondering if my mind is playing tricks to make me feel better (for having a duh moment) or if the higher octane might make a little difference...?
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Potentially, the engine computer may be able to advance the timing more with the premium, allowing for improved performance.
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I wondered about that. Does the computer adjust the timing in real time, and how does it determine what is optimal?
"hyundaitech" wrote in message
Potentially, the engine computer may be able to advance the timing more with the premium, allowing for improved performance.
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On Saturday, June 29, 2013 12:23:32 AM UTC-4, Victek wrote:

The computer is constantly adjusting ignition timing. It uses input from a piezoelectric sensor to determine when spark knock occurs, retarding timing when knocking occurs and advancing timing when it doesn't.
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"hyundaitech" wrote in message
On Saturday, June 29, 2013 12:23:32 AM UTC-4, Victek wrote:

I thought it might be something like that. Does using a higher octane translate into measurably better mileage or is it just about a little extra power? Thanks!
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On Sunday, June 30, 2013 3:00:32 PM UTC-4, Victek wrote:

ra

I'd suspect no measurable increase in fuel economy, but it's hard to say fo r sure without an analysis. And it's likely to vary from engine to engine. You could spend a few extra dollars for a few tanks to find out. I'd be interested in the results if you do it.
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I'm planning on checking it out. I'm going to use 89 octane for a while and I have a a couple of longer, highway drives coming up where I can more accurately track the mileage. It will be a bit but I'll post back.
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I see slightly better gas mileage when I do 1/2 87 & 1/2 89 octane and long 200+ mile trips with a loaded trunk.
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"hyundaitech" wrote in message
On Sunday, June 30, 2013 3:00:32 PM UTC-4, Victek wrote:

I did get around to making those longer highway drives and kept track of mileage to see if 89 octane would make any measurable difference. I can't say that it did, but I'm not sure it didn't either. What I did realize is there are too many variables, eg air conditioning On/Off, traffic slowdowns (shifting into lower gears) different load in the car than normal, etc, - impossible to conduct a controlled test. C'est la vie :-)
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On 9/16/2013 12:59 PM, Victek wrote:

I'm told that a tank or two a year of Shell Premium is good to keep the fuel injectors clean
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The newer Elantra can run slightly better with anything a tad better than 87 octane. So yes, a bit more punch but you're not exactly going to be qualifying for pole position. Unless an engine's compression ration is designed for 89 octane, you'll not be getting the full advantage from it. This is especially true for 93 octane. My buddy had a Ford...Contour SVT, I think, that had an engine tuned for and requiring 93 octane. I would imagine with today's gas prices, he's since dumped it for something using 87 octane. I blend of 87/89 would probably yield a nice balance. If I also remember correctly, the higher octanes also yield higher heat so you can expect the engine to run hotter than normal.
- Thee Chicago Wolf [MVP]
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Thanks for the reply and info.
"Thee Chicago Wolf [MVP]" wrote in message

The newer Elantra can run slightly better with anything a tad better than 87 octane. So yes, a bit more punch but you're not exactly going to be qualifying for pole position. Unless an engine's compression ration is designed for 89 octane, you'll not be getting the full advantage from it. This is especially true for 93 octane. My buddy had a Ford...Contour SVT, I think, that had an engine tuned for and requiring 93 octane. I would imagine with today's gas prices, he's since dumped it for something using 87 octane. I blend of 87/89 would probably yield a nice balance. If I also remember correctly, the higher octanes also yield higher heat so you can expect the engine to run hotter than normal.
- Thee Chicago Wolf [MVP]
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Well, I can say for certain that 89 gave me *much* better MPG than 87 did on a1400 mile trip I just came back from. I went down to St. Louis and filled up with 89 and was getting around 39MPG doing 70 on 55 South. After that, I went down to Memphis on 55 south and was doing 75 the whole way and was getting around 37.5MPG. On the way back I filled up with 87 and MPG went down at least 5%. So yes, it seems at least on highway driving MPG improves with 89. Mind you this was with 2 adults, one kid and two suitcases in the trunk. The trip back I think I only added around 10-12lbs in souvenirs tops.
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wrote:

Maybe.
On my 24 mile trip from home to work, I get 31 to32 mpg on the way home, but only 29 to 30 mpg on the way to work. I've checked this on two cars under the same conditions on the same day. There is an altitude difference between the two places.
If you want to try again, use the same points to be sure it is equal.
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Well, it's 300 miles to St. Louis from Chicago and 300 miles to Memphis from St. Louis. 80 degrees, give or take, for outdoor temp. I had the cruise control on the whole time and only stopped once in between either drive so altitude and all that aside, I think it had more to do with octane than altitude in my case. I did reset the MPG Average counter a few times on each trip to make sure it wasn't giving a false average. Just sayin'.
- Thee Chicago Wolf [MVP]
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wrote:

Chicago 583 feet Memphis 341 feet.
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http://www.ehow.com/about_6744997_effect-elevation-gas-mileage.html
- Thee Chicago Wolf [MVP]
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On Tuesday, July 30, 2013 9:13:00 AM UTC-4, Thee Chicago Wolf [MVP] wrote:

I think you're missing Ed's point. The link you provided refers to differe nces in fuel economy driving at one elevation vs. another. Ed is referring to the fact that you're driving uphill (overall) in one direction and down hill (again, overall) in the other.
This is a real phenomenon. Every time I check highway fuel economy in a ca r here, I drive several miles northbound on the expressway and then make th e identical trip southbound. Every time, the fuel economy is at least a co uple miles per gallon better on the southbound trip.
That being said, I'm tempted to believe that the effects of a .01% (yes, on e hundredth of a percent) overall grade are anything more than minimal and that the difference is more likely due to the octane difference or the spee d difference you cited.
The bigger question, of course, is whether the fuel economy difference woul d pay for itself. If we assume the entire 1.5 MPG differential is due to o ctane, over the 1400 mile trip, I calculate you would have saved about 1.5 gallons of gas, or about $7. If we take a price differential of $.20 per g allon between 87 and 89, you used a little more than 35 gallons, or a littl e more than $7. All in all, even assuming the best possible results out of this scenario, it looks like we still pretty much break even.
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hyundaitech wrote:

You will never convince people who believe in things like this. The variables incurred in normal driving will swamp out almost any difference you can imagine from gasoline octane or any of the gadgets that claim to increase mileage. Scientific test after scientific test show that such claims are bunk, but that won't affect the true believers.
The only way higher octane will affect gas mileage is if you are running in conditions where the engine is detonating or preigniting and the ECM has to retard the timing. If this is the case during steady state cruising on the interstate, then you have some serious engine problems that need more than higher octane gas to correct.
Matt
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The difference may not be great, but it seems to me there could be different optimal timing settings determined by the computer for different octanes. Whether or not it's the case for a particular engine I expect could only be determined under laboratory conditions to eliminate all the "real world" variables. In my own case I "think" I perceive a small improvement in "get up and go" when I use 89 Vs 87, but the mind is easily fooled. There's a real difference between octanes though, as opposed to flim flam devices that claim to improve mileage.
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