87, 89, or 91???

remember back in the days i read a article from C&D,
it says something like if the engine design specifically for 87 octane...filling other grade of gas will just decrease the performance....


p.s. sorry for my broken english, since its not my first language :oops:

 

The Scion xB uses Unleaded Gasoline, Octane rating 87 (Research number Number 91) or higher as it says on the Scion Owners Manual. I use 87 (regular unleaded) on the xB. Works fine.

 

so the manual doesnt specifically recommend which grade?

 

it says 87 or higher, that's it. and the ECU is programmed to work well with 87 , so if you put higher octane, it probably won't make any difference with a stock scion engine.

 

thats what i wanted to kno....cool...thanks eric :D

 

The gas prices here in sandiego are 87 octane $1.67 for 91 octane $1.87.

I love this car. Great mileage

 

i use pemex gas and my xb runs great lol

 

I've used 93 octane the last two tanks I put in and there is a noticable difference. About 40-50 miles more per tank: about 4 more MPG. That is over 87 Octane which I used for the first few tanks.

I haven't dont the math to find out if it's cost efficient, but it's useful to get those extra miles per tank on a long trip.

-Gage

 

I think that difference is just in your mind--maybe you have driven differently in the last two tanks?

Honestly, I don't think the different octance ratings will increase mileage on any particular car.

The car uses and will run best at 87 octane...any higher grade you go, you'd just be wasting money.

 

Well, perhaps so, perhaps not.

Modern cars are designed to adjust themselves for various grades of fuel. Some cars specify 92 octane fuel, but will run on 87 with a reduction in efficiency.

It is possible that the Scion will run better on higher octanes, but you would have to run some comparisons to make certain. You would have to run a set route, maintain set speeds under similar conditions to get good data. Just calculating mileages from one fueling to another isn't accurate enough unless you are a very consistant driver (as in a long commute or somesuch).

George

 

AGREE!!!
if the car designs for 87 then go with 87, which i think what xB suppose to run...(it's cost-efficient car remember?)
people from my accord club (av6) did the comparasion between different grade of octane...dyno tests turn out 87 gave more horsepower and torque at the wheel than 89 and 91..

 

I've had SEVERAL cars, and I have noticed this on all my cars.
With the Scion tank being so small, I'd prob run Super most of the time.
$15.00 fill up, better than $42 on an Avalanche!

 

There are numerous articles in magazines, etc that show/inform us that the difference is pretty much none--just use what your engine needs. There was even an article in Super Street about it!

Of course, people 'think' they get better results from paying more at the pump..afterall the guys at the gas station aren't going to tell you that all you need is 87...hell, they would love to sell JUST 91 if they could. If you guys are putting Premium gas in the ECHO engine...what would you put in something "high performing"?! It's pretty much self explanatory in the owners manual..."87 or higher". Well, they can't say below 87--because that doesn't exist, and they can't say JUST 87 because higher grades will work just as well. Believe me, there is a reason why a Integra GSR/Type R lists "only Premium" in it's owners manual as opposed to an Integra LS which lists "87 and up".

 

The amount of octane in gasoline has nothing to do with how "explosive" it is, all octane ratings provide the same amount of oomph. The octane actually delays the speed of combustion... so the more octane in the gas the longer it takes to completely burn.

Engines are designed to work on a specific octane rating... the ignition timing is set for it. If you use a high octane on a car designed for a low octane you will decrease the performance because the burn won't happen until the piston as past the regular point of ignition. Bam -- loss of power and efficiency.

If the manual says 87, stick with 87.

I stay away from ARCO though, my car actually runs worse on it for some reason.

Darren

 

There is a germ of truth in what you are saying, but some of the gaps need to be filled to understand the issue completely.

Octane is a hydrocarbon compound with 8 carbon atoms, hence the "Oct" prefix.
Heptane is a hydrocarbon with 7 carbon atoms, hence the "Hept" prefix.

(for petroleum engineers, yes there are more technical names for these, but let's keep it simple!)

You mix these two compounds to get standard fuels of various octane ratings. 50/50 heptane/octane gives 50 octane, 20/80 gives 80 octane, and pure octane is 100 octane.

These chemicals are rather expensive and you wouldn't want to bear the cost of running them in your car.

Fuels are tested in a test engine. The test engine is actually run by an electric motor for consistant speed. The neat thing about the test engine is that the head can be screwed down to vary the compression ratio. The engine is run on the fuel to be evaluated and the head is screwed down until the engine starts to pre-ignite or "ping". The setting is noted, and then the test is repeated with various mixtures of heptane/octane ("standard fuels") until the same point of pre-ignition is reached. The percentage of octane in the standard fuel that produces the same pinging behavior is the octane rating of the fuel.

What is pre-ignition? Simply having the fuel ignite all by itself without the intervention of the spark plug. You don't want this to happen, as the fuel burns all at once, causing very high pressures in the combustion chamber which can break things. The higher the octane rating, the more resistant it is to pre-ignition, and that is really the only difference that octane makes. High-octane fuel has a slightly smaller flame propogation speed than low-octane fuel, but not enough to make any difference in a real-world engine.

Toyota specifies that they have designed the Scion engine to run on 87 octane fuel. If that is truly the case, you will not get any advantage in running 91 octane fuel.

Nevertheless, some claim that they have better performance or mileage with 91 octane. How can that be? Well, one way this could happen is if they had a tankful of "bad" 87 octane that was actually lower in octane. The engine's computer would adjust the engine to run on the lower octane fuel, resulting in lower mileage and performance, but not doing anything permanently bad. When the person fueled up with 91 octane, the computer simply readjusted to the normal 87 octane specs and produced better performance and mileage.

Another scenario is that Toyota pushed the envelope a bit with the engine computer, which means that the engine actually does benefit from higher octane fuel. There's nothing magical about the number 87 and they might well have designed it for 87.5 or 88.

How do we tell for sure? All we need to do is to get a Scion, put fuel of a known, measured 87 octane in it, and run a set schedule on a test track. fuel the same car up with 91 octane and run exactly the same schedule on the same track. The results will be quite clear.

Another way to do it is for someone to keep long-term records of a vehicle in regular commuter service. The quirks in the data will tend to average out, so comparisons can then be made between the fuels.

For those who feel that one brand of gasoline is better than others, be aware that all the refiners freely trade gasoline back and forth with each other to meet the needs of their retailers. That "high quality" Union 76 fuel you are putting in your tank may well have come from an Arco refinery! :)

George

 

Excellent explanation on it. So when was our assignment due on this again?

I say just keep track of your gas mileage with real calculations (not rounded calculations off the top of you head) and see for yourself but if the factory says 87 then why fight it.

 

I agree, and I'm pumping 87.

I do keep a logbook in which I record maintainance and fuel use. A sudden decrease in mileage is often a precursor of more serious problems. I've only run two tankfuls through the car, with mileages of 28 (city, with my wife driving) and 26.5 (city, with mostly me driving). Not bad for a new car that advertises 30.

George

 

It's definitely not in my mind, it was right there on the odometer.
As for difference in driving, I cany drive differently if I tried. And I HAVE tried. I gotta get from point A to point B as fast as possible, apparently as my foot wont let me drive any other way.

The ONLY possible reason other than grade of gas is engine breakin. I might be getting better milage as the engine breaks in. Or it may be the gas. Who knows.

And as for the "use the gas the car is made for" and "the manual says 87" - the manual says "AT LEAST 87" which means that is the LOW end of gas to use, not the TOP END. That says to me that if you are cheap, use 87 but nothing less, but the car can benefit from more.

-Gage


-Gage

 

It is true that you get better gas mileage with time and miles. The dealer told me that i should be able to hit the advertised 30/34 MPG after 4000 miles or so on my Scion.

I shall wait and see. I've been averaging about 28MPG on full tank freeway/city combined. In addition, i've been using Shell gas 87 Octane. Shell is promoting some new stuff in their gas that promotes better gas MPG.

I have 980 miles on my baby, and i shall see how things turn out near 4000 miles.

 

Its true about getting better gas mileage as you get more miles on. Right now I'm at 5500 miles total and when I filled up my tank before my most current one I got an AMAZING 33.37 MPG! I thought that was a fluke but I just filled up today and I got 33.83 MPG! I thought I drove it a bit harder and used the A/C more so I didn't think I could've topped my previous MPG but I did....in fact, I've even been doing more city driving since I have to drive about 5-6 miles to get to the freeway from my place instead of the 2 miles it took me at my previous place.