I run strictly 93 and run 80mph 75% of the time. I still avg 32 miles to the gallon. Just my .02

 

ok, lower octane fuels ignite at lower temps....
compression causes heat...

(can you see it yet???)

if you run low octane fuel in a high compression motor you get knock. why, because the heat from compression prematurly ignites the fuel...

this is why we have a knock sensor on our cars....
the ECU will adjust timing to prevent knock....
so, you do not need to run high octane fuels.
if it makes you feel better, go ahead...

 

correct, the ECU controls timing

 

hmmmm.....your logic is dead on but did you read what you typed? If the engine pulls back timing then there is less power. So if you don't care about power run lower octane if you do run the higher.

 

This type of octane discussion always makes my head hurt every time it comes up on a forum. Modern cars are tuned for a certain octane. Going over that octane does nothing. Going under that will either cause the knock sensor to kick in and the ECU will retard the ignition, killing performance in the process. Unless of course you don't have a knock sensor and then you just fry your pistons.

Scions are all tuned for 87 octane to my knowledge. Runing 91 or 93 will yield zero improvements.

If you want a more technical explanation this is a good write up:
http://www.bajajusa.com/Who%20Needs%...ane%20Fuel.htm

 

The scion engines despite their higher compression are setup to run 87octane. The base map(fuel/ignition curves) in the ROM or EEPROM is setup at 87 octane not 91or93. So it wouldnt pull any more timing then is already not there... running higher octane will increase the "margin for error" on hot days but not anything you'll feel in an NA motor that small

Peace

 

I love the points stated in the Shell website. You will NOT get more performance out of this higher grade fuel. If you want to talk about the energy that the fuel contains, the higher the octane the less energy the fuel contains. Higher octane means that it is a more stable fuel. Think about it as a bomb. Which material contains more energy a pound of black powder or a pound of Uranium 235? The only thing that makes higher octane high performance is the fact that it resists detonation when exposed to high heat high compression conditions.

 

I hear ya there... It always amazes me that people know more than all the petroleum chemists and engineers just based on a couple tanks of gas, a guesstimation on the ___-dyno and some "precise" math that always manages to support their point or the reliable family experience anecdote...

Unknown voodoo magic rumors will trump science any day...

 

I'm not big on retarded horses.

 

wow.....south illinois.......where i am and where u wanna buy gas....

87---$1.62 gal

 

if vvt-i deals with ignition then why is it VARIABLE VaLvE TIMING???? at high rpm's...vvt-i slows the intake VALVES and exhaust VALVES to let in more air/fuel and put out more exhaust.......

 

i think the best quality gases go amaco, sunoco, then probably hess and mobile then downhill from there. my dad works for a pipeline company basically amaco uses no dyes or additives to distinguish from other gases and keep their gas separate from other companies while sunoco is second best and so on. a lot of cheaper gas stations take there gas from a collective tank basically as long as they get the octane they are asking for they are happy but overall unless u have a performance engine or the manufacturer recommends it a higher octane just means more money. if your stock scion does seem to perform better on higher octane gas u may want to look into a tuneup

 

Speaking from personal experience.... Before getting the tC, I was driving a 94 ford probe SE. Well, definitely not a high performance engine. However, there was quite a difference if I pumped 87 and 93. With 93, I always have a smooth and more powerful launch, while 87 would hesitate especially during launch and highway acceleration suck too!

Now that I own my tC and live in CA, I was wondering my choice of fuel. I always use 91 Oct, but one day I decided to try 87 Oct instead. The first thing that I notice was that my TRD exhaust tip was full of black nasty carbon build up after about 25 miles of driving, right after I went off the the gas station. However, with 91 Oct, I don't really have that kind of nasty build up so quickly. Yes, with 91 Oct I still have carbon build up but that is not obvious until the 2nd pump (about 600 miles). I think some of our scionlife bro here are right, higher oct fuel is a cleaner feul. It's gonna be good to our fuel injection system and valves. Power wise, I do not really notice a difference but I am not an aggresive driver, anyway.

Just my $0.02

 

As many people have already stated, the only thing a higher octane is good for is resisting predetonation.

As long as ignition occurs when your engine wants it to (as in when the spark plug fires), 87 octane will produce the same amount of power as 89, 93, 94 or even 120 octane. If you have a stock tC (consider yourself stock if all you've changed on your engine is your intake and/or exhaust, or anything short of putting on a turbo/supercharger or otherwise changing your compression ratio considerably), I promise you that ignition will occur only when the spark plug fires with 87 octane. Higher octane gasoline will not make your car any more powerful. Save your money and spend it on something that will actually improve your car's performance.

--Mike

 

ok, i dont want to flame but vvt-i has absolutely nothing to do with octane and you are 100% wrong if you beleive that the vvt-i system will utilize the higer octane gas and somehow raise the compression or change the tining for better performance. howStuffWorks.com explains this very well...as my explination would probably confuse you:

"It turns out that there is significant relationship between the way the lobes are ground on the camshaft and the way the engine performs in different rpm (rotations per minute) ranges. To understand why this is the case, imagine that we are running an engine extremely slowly -- at just 10 or 20 rpm, so it takes the piston seconds to complete a cycle. It would be impossible to actually run a normal engine this slowly, but imagine that we could. We would want to grind the camshaft so that, just as the piston starts moving downward in the intake stroke, the intake valve would open. The intake valve would close right as the piston bottoms out. Then the exhaust valve would open right as the piston bottoms out at the end of the combustion stroke and would close as the piston completes the exhaust stroke. That would work great for the engine as long as it ran at this very slow speed.

When you increase the rpm, however, this configuration for the camshaft does not work well. If the engine is running at 4,000 rpm, the valves are opening and closing 2,000 times every minute, or thirty to fourty times every second. When the intake valve opens right at the top of the intake stroke, it turns out that the piston has a lot of trouble getting the air moving into the cylinder in the short time available (a fraction of a second). Therefore, at higher rpm ranges you want the intake valve to open prior to the intake stroke -- actually back in the exhaust stroke -- so that by the time the piston starts moving downward in the intake stroke, the valve is open and air moves freely into the cylinder during the entire intake stroke. This is something of a simplification, but you get the idea. For maximum engine performance at low engine speeds, the valves need to open and close differently than they do at higher engine speeds. If you put in a good low-speed camshaft, it hurts the engine's performance at high speeds, and if you put in a good high-speed camshaft it hurts the engine's performance at low speeds (and in extreme cases can make it very hard to start the engine!).

VTEC (which stands for Variable Valve Timing and Lift Electronic Control) is an electronic and mechanical system in some Honda engines that allows the engine to effectively have multiple camshafts. As the engine moves into different rpm ranges, the engine's computer can activate alternate lobes on the camshaft and change the cam's timing. In this way, the engine gets the best features of low-speed and high-speed camshafts in the same engine."

This is from a search on VTEC...which is the EXACT same thing as vvt-i. Also, The ONLY time higer octanegas will increase performance is if you have a predetonation or ignition problem. Say what you want...on a stock engine higher then needed octane is useless. "cleaner" gasses are the results of detergents, not octane. I just wanted to clear up the vvt-i thing because the octane battle will never end, so let people think what they want...ignorance is bliss

 

I thought tC engine is 9.6:1? If it is, then 87 should be fine. If it is over 10:1, then it'll Need 93.

"If your car requires high-octane gasoline and you habitually use regular gas because the engine exhibits no sign of knock, you’re outsmarting yourself. Most modern, computer-controlled engines include a knock sensor that detects knock and retards the ignition timing, causing the spark plugs to fire slightly later in the cycle. This typically prevents abnormal combustion and knock, which allows vehicles specified for premium fuel to run on lower-grade gasoline if it is all that’s available. While this removes the immediate hazard, it’s a bad idea to make a habit of running a vehicle on gasoline of lower-than-recommended octane. Retarding the spark causes a richer fuel/air mixture, which decreases fuel economy, increases emissions, causes the engine to run hotter, and reduces the longevity of both the engine itself and the catalytic converter. The money you save by pumping low-grade fuel into a car that demands higher octane is lost anyway, in decreased fuel economy and possibly gradual damage."

http://www.cars.com/carsapp/national...odaysgas1.tmpl

 

That's odd cuz the xB runs a 10.5 to 1 and recommends 87.

 

Run 2 tanks of regular through your car.
Go to local dragstrip and collect time slip.
Run 2 tanks of Sunoco 94 Ultra through car.
Return to local dragstrip.

Read disappointing time slip.

Go home with puzzled look on face.

Refill with regular.

 

Correct but it has to do with the timing of the "valve event", when it opens... the only way to have a valve open longer is to change the duration of the cam lobe it's actuated by... and I'm pretty sure vvt-i only works its mojo on the intake valves...

Peace

 

I am begging to differ on that one bro...
vvt-i cahnges the cam phasing or when the valve event opens based on a baseline setting. vvtl-i the difference being the L in there is the exact same thing as an iVTEC engine...

So VTEC= changes lift(amount valve opens into the cylinder, they also have a different phase and duration than the low rpm lobe but that cannot be changed its ground into the cam shaft)
vvt-i= changes cam phasing like an auto adjusting cam gear on the intake camshaft
vvtl-i= changes cam phasing on intake cam as well as changing valve lift and duration(how it does this is very similar to VTEC)
iVTEC= same thing as vvtl-i(some iVTECs only have VTEC on the intake camshaft, RSX-S and TSX are only USDM cars that have iVTEC with VTEC on both intake and exhaust camshafts. I dont know if any toyota engines have it on both though)

Peace