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Old 10-26-2008, 10:11 PM   #1
dg4rez
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reg or mid

there is a gas station that I always filled up at here in vegas, that if you paid in cash they will give you midgrade for the same price as regular.

will midgrade hurt my yaris? help my mpg? not worth it? thoughts? midgets?
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Old 10-27-2008, 12:36 AM   #2
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won't hurt it at all... There is some speculation that if you reset the VVTI settings and consistently run 89octane that you might get slightly better gas milage.... but thats only the case if your engine has automatically retarded the timings due to engine knocking caused by 87octane gas.

I wouldn't worry about it too much, but would take them up for that offer as long as I had cash on me.
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Old 10-27-2008, 01:07 AM   #3
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Quote:
Originally Posted by talnlnky View Post
won't hurt it at all... There is some speculation that if you reset the VVTI settings and consistently run 89octane that you might get slightly better gas milage.... but thats only the case if your engine has automatically retarded the timings due to engine knocking caused by 87octane gas.

I wouldn't worry about it too much, but would take them up for that offer as long as I had cash on me.
what you mean reset the vvti settings?
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Old 10-27-2008, 11:49 PM   #4
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Quote:
Originally Posted by dg4rez View Post
what you mean reset the vvti settings?
i dunno how to do it, but the computer that controls the VVT has some sort of intelligence (the i in VVTi) that tries to optimized the performance of your engine based on the way you normally drive.

So... something to do with the valve timings. Anyways, if the engine starts to knock.... the engine adjusts to not be as agressive... and thus loses a tiny bit of power to make up for the knocking.


i'm not an expert on this, nor would I ever claim to be... I just remember reading about this before the site got hacked.


hopefully somebody will chime in.
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Old 10-27-2008, 11:57 PM   #5
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Just do as the manual says, 87 octane... Midgrade or regular depends on where you live. Just look at the octane...
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Old 10-28-2008, 08:06 AM   #6
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Higher octane gas than the manual lists will lower your FE if your driving for FE and will usually cost you more money.
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Old 10-28-2008, 11:26 AM   #7
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Higher octane fuel is useless in our engines. It may burn a little cleaner, but it won't improve FE nor overall performance. Higher compression engines can take advantage of the higher octane fuel, but not our car. Pay with credit card, and get the points!
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Old 10-28-2008, 05:49 PM   #8
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I have always used the lower grade with no problems. Do a test and see which works best for you.
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Old 10-28-2008, 05:53 PM   #9
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Quote:
Originally Posted by natethegreat38 View Post
Higher octane fuel is useless in our engines. It may burn a little cleaner, but it won't improve FE nor overall performance. Higher compression engines can take advantage of the higher octane fuel, but not our car. Pay with credit card, and get the points!
He speaks the truth.
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Old 10-28-2008, 06:18 PM   #10
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2007 Yaris Manual
Quote:
OCTANE RATING
Select Octane Rating 87 (Research Octane
Number 91) or higher.
Use of unleaded gasoline with an octane
rating or research octane number lower
than stated above will cause persistent
heavy knocking. If it is severe, this will
lead to engine damage.
If your engine knocks...
If you detect heavy knocking even when
using the recommended fuel, or if you
hear steady knocking while holding a
steady speed on level roads, consult your
Toyota dealer.
However, occasionally, you may notice
light knocking for a short time while accelerating
or driving up hills. This is normal
and there is no need for concern.
GASOLINES CONTAINING DETERGENT
ADDITIVES
Toyota recommends the use of gasoline
that contain detergent additives to
avoid build−up of engine deposits.
However, all gasoline sold in the U.S.
contains detergent additives to keep clean
and/or clean intake systems
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Old 11-19-2008, 12:46 PM   #11
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I used to use 87, and it was fine. While looking to achieve better FE, I switched to 89, and my MPG went from 38 up to 46, with a one time stint of 51. The motor seems to run quieter on the highway and idle smoother, too. For the extra 4c per gallon, I think it's worth it.
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Old 11-19-2008, 12:51 PM   #12
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Old 11-19-2008, 01:47 PM   #13
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Interesting thread. One thing I've always noticed when going down to Central America -- I have family down there -- is that people tend to always buy at least midgrade gasoline, regardless of what they're driving (lots of yarises down there, too). I'm not totally sure why this is (cultural difference? difference in gas quality?) but if you buy regular people will look at you like you're crazy. Or, maybe they thought I was crazy for other reasons...
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Old 11-19-2008, 09:42 PM   #14
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I use Shell V-Power, and am getting 37-40mpg, driving pretty hard.

The manual is quite interesting. It notes that detonation (though light) may occur under hard acceleration or climbing hills using the recommended 87 octane. This will retard the ignition timing, and cost power. It is not stated in the manual what the ambient air temp was when the testing was conducted, but I'd assume it wasn't on a freeway onramp on a SoCal summer day. That said, I feel our car's 10.5:1 compression is too high to get the most power from out little 1NZ-FE on 87 octane fuel. As the manual infers, under certain conditions, the engine is dealing with detonation using the MINIMUM octane fuel. Just because you don't hear knocking doesn’t mean it's not happening. All the manual says is that the car's ECU can handle the light detonation that may accompany the use of 87-octane fuel to the point that it won't damage the engine.

That said, I know that driving style and ambient conditions affect the chances of detonation, and I know that many people are getting killer fuel economy running regular fuel. All I contend is that in my car with my driving style in my local, 91 octane actually gives me an additional 2-3 mpg, and provides an extra buffer against detonation. This makes a tank of premium the same price or cheaper (per tank) than regular...plus the car gets a higher dose of detergents! SCORE!!


Note: The lowest ignition advance I have ever seen (via scangauge) is 17 degrees BTDC (hot afternoon on the 210 East just west of Verdugo road...you guys in cali know the hill). Normally the lowest advance I've seen is 24-27 degrees BTDC. These are at highway speeds, and leaving lights...at a stop the ignition gets retarded to just a few degrees +/- of TDC....I'd assume to lessen load on the engine and increase idle fuel economy. Cruising I normally see 37+ degrees of ignition advance.



Anyone with a scangauge car to share some data?

Last edited by jkuchta; 11-20-2008 at 12:13 PM.
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Old 11-20-2008, 11:54 AM   #15
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Quote:
Originally Posted by VTE-070 View Post
I used to use 87, and it was fine. While looking to achieve better FE, I switched to 89, and my MPG went from 38 up to 46, with a one time stint of 51. The motor seems to run quieter on the highway and idle smoother, too. For the extra 4c per gallon, I think it's worth it.

Sorry, but I have to pull out the BS Smiley:

A 21% gain in MPG just by switching to the mid grade gas is just not going to happen. I would guess that you were driving more conservatively with the slightly more expensive tank of gas which yielded higher MPG. Besides that is only one trip (??) or is it an average??

Sorry dude, I don't buy it seeing as we have hypermilers on here that are barely achieving 46 MPG with mods and hypermiling tactics...
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Old 11-20-2008, 01:42 PM   #16
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i concur!
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Old 11-21-2008, 03:49 AM   #17
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Octane is the relative measure of a fuel to "knock" or ignite on its own rather than by spark. The rating is derived from a "research motor" that compares the rate knock with respect to octane (100) and hexane (0). I don't know if it's still being done that way or not - maybe there is a model that can be used on computers - but this was the traditional method.

The term "knock" is from the pinging sound that the process generates in a motor, similar to metal striking on metal. One the ways to troubleshoot an engine with a knock sensor is to strike the side of the motor block with a metal tool. The spark timing should adjust accordingly.

Another name for knock is "spark knock" but it is known as "pre-detonation" too.

Pre-detonation is, as far as I can recall, is an effect when the fuel is combusted "prematurely", usually by some condition inside of the cylinder like a "hot spot", burr or carbon deposits. Sometimes a mixture which is too lean will cause "isolated" areas in the combustion chamber that are more vulnerable to predetonation.

There is "detonation" which is more destructive than knock. The fuel flame front exceeds the speed of sound. Damage can occur to the head of the piston and other components. The fuel air mixture should "deflagrate" or burn at a speed lower than sound. Fast but not at an explosive rate. In case anyone cares "hemis" (engines with hemispherical chambers, something that was usually done by Chrysler) are exquisitely sensitive to detonation, especially with lean mixtures. Hemis were not all that they were cracked up to be.

Timing changes are retardation of spark to prevent "knock". The spark comes sooner to ignite fuel charges before the knock can do it. You loose power this way and generate more heat in the motor. Sometimes you get a "vicious cycle" where the retardation can cause more heat, leading to more knock, leading to more retardation. However the ECU will change the fuel mixture, which ought to help.

In the bad old days before we had ECUs (before 1980) you could have some real messes with motors that were supposed to run lean to pollute less but could not adjust mixtures on the fly. Especially us knuckleheads who didn't know how to find vacuum leaks. The "lean lope" was the first warning sign, then we'd discover knock.

I don't know if VVT has anything to do with solving knock. Who can say? I would not be surprised if there were some "operating regimes" that could use a change in valve timing to improve performance or eliminate knock. I have a lot of confidence in Toyota's engineers - they keep hitting them out of the park.



I don't see much of an advantage of driving a Yaris with mid and premium grades of gasoline UNLESS you intend to run it "hard". In which case the resistance to predetonation might help you avoid the power loss due to retarded timing.

Me, I don't bother using mid level or premium grades unless I know I'm gonna be hammering it and it's hot outside. In other parts of the year it's just a waste of money to me.

Gene
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Old 11-22-2008, 11:24 AM   #18
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After reading several conflicting threads, I did a 3 tank test this fall.
I have a 6 mile commute each way, with lot's of hills and frequent starts and stops.

On 87 octane with Ethanol, my last three tanks were:
40.44 mpg
38.72 mpg
39.17 mpg

On 89 octane with Ethanol my 3 test tanks were:
37.41 mpg
36.76 mpg
36.65 mpg

The next three 87 tanks came back up slightly, all above 38 mpg.
For my commute, I got better mileage using 87 octane. Also, I noticed longer crank times, with 89 on colder mornings, and higher GPH numbers at idle across the board.
No earth shattering conclusions here, but it does confirm Bailout's claim that if you drive for FE your mileage will go down with higher octane.
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