all this hubub about octane.....all that itll do performace wise is allow the knock sensor to retard more, thereby giving you maybe one extra horse

brent

 

wow im in cali and i can get 87 for 195 so thats not too bad i can live with that alot better than 230 like it was a while back

 

It was found out that the Scion xA/xB produce 108HP/105 Ft. Lbs to the flywheel using 91 Octane. meaning with lower than 91 octane you get less power.

 

dont know about that but i suppose i'll take yer word on it
the owners manual does reccomend 87 tho. if it worked better with higher octane it'd reccomend higher octane. if u need higher octane buy the boosters they works better and are cheaper than higher oct gas

 

Power or no power, as long as combustion is stable and there is no knock or ping. . . that's THE most important thing about the fuel.

 

Trust me, it will go back up. . . I guarantee it!

 

 

1.59 for 87 here in MD, oh by the way, 93 burns easier, means, it last less, and it wont make a big difference, dont waste your money.

 

here in san diego, gas prices are horrible...but i still go with the highest octane

 

So what is the HP produced with lower octane number?

Well ... With higher compression engine, I can see why we need to use higher octane fuel. But with Scion ... ? Why?

According to a journal (which made perfect sense to me. .. but I bet there are many who would disagree ... and I don't even remember what/where the journal was from ... so don't flame me.... ) , that I read a while back, it takes less heat/pressure to have combustion with lower octane numbered fuel. (My understanding is, that with higher octane, you can apply more pressure, without worrying about knocking...) ... Therefore, with low compression engine, such as our Scion's (haven't checked the exact number ... but I'm pretty sure it's not high ...) we can get the optimum ignition with lower octane fuel, such as 87 ... anything lower, we might get knocking, so ...

Of course, with higher octane, we probably get little bit cleaner fuel ... but I don't think it really matter .... anyways. .... just my 50c...

 

Our compression is 10.5:1 not exactly "low" most people I know seem to think thats pretty high.

 

Where is that documented?

 

from my understanding, high octane does not increase performance, but prevents predetonation, which occurs in highly tuned engines. However, the idea is that if you use higher octanes, your engine can safely advance the timing (increases power) as the computer senses that the fuel is stable enough at that timing to not predetonate (knock). Running lower octanes (although safe, and perfectly fine) will force your computer to run of the safest timing, which will have the slowest performance. But, I personally feel that the difference is VERY minimal with this engine. Running a larger engine that USES MORE FUEL would have a more significant impact. Everything is in % gains, and the price does not justify the gain. Saving the money for restriction removing enhancements makes more sense to me, as they will generally increase mileage as well.

In older cars without knock sensors, going above specifications often led to reduced performance. Yet people always follow the marketing rule, more $ = better product.

If you throw in race gas, you might feel a difference.

 

That's exactly it. Higher performance engines do not use higher octane because it has more "power", they use it because they can run a higher compression ratio and different ignition curves, which then makes more power.

 

I think your better off trying different gas stations with 87 octane. I live in NY and was strictly using Hess but then I started to get this hesitation problem when switching gears. I was thinking maybe the throttle linkage cable was getting stuck or maybe my floor mat was getting stuck under my accelerator pedal. I checked those things out and found nothing wrong with them. I figure I should try using a different gas station. Always heard good things about Mobil gas so I figured I'd try it. After 1-2 tank fulls the hesitation is gone and the cars feels like it accelerates smoother and shifts are a lot smoother, I have a 5 speed. I would try that before paying the price for premium. Could be just the gas. Made my wife stop going to Hess also.

 

10.5:1, in my opinion is kinda up there. Scions are equiped with VVT-i which advances and retards the timing/ignition +/- 60 degrees. So technically using higher octane lets you use VVT-i more than when you use lower octane, Because 91 octane is a cleaner and slower burning fuel that 87 octane (I learned that in school, and I've read that in various other atricles). So if you have a higer compression engine you should use a high octane. I consider anything higher than 10.0:1 high compression(you may disagree, but thats my definition) I can't remember where I read that the Scions were tested on 91 octane but I"ll search for it and post it when I do.

 

VVT-i has nothing to do with ignition timing, it only changes the phasing of the intake camshaft. It only responds to engine speed and load. It won't affect the engine's ability to take different octanes.

 

just so people know 10.5:1 is high. most older v8's are close to 8.0:1 or so and high comp race motors are near like 11-12 . rotories are higher than that and diesels are insanely higher. but yes.

 

I think Toyota just likes working with high compression ratios. The compresion ratio in the Matrix XRS is 11.5:1

 

Thank you, jeeze people and their hype... Good call dude.
Although race gas is typically leaded and will destroy your O2 sensor.

jodanscion you are right on the money and thank you for being an educated salesperson! If I know a lot more than the salesperson I dont buy from them, because they are lazy...

I think it might be because it makes more power

Peace