I only use Shell. When I tried 93, I used several tankfulls in a row so I knew it was pure 93. Had no difference in performance.

 

So you drove the majority of the time such that the ECU would have been intervening on 87 octane but was not on 93 octane. Like continuous heavy throttle in mountains or at high Interstate speeds. No difference in power or mileage. So fact trumps theory.

 

For myself, the diff was noticable (by the box not forcing itself into 3rd to maintain 35MPH on the long uphill on the arterial closest to the apartment, as it did consistantly with 87) on the first fillup with 91 octane (that was an 8.2 gallon fillup).

After the second fill with 91 I reset the ECU to make sure it would choose curves based only on the current fuel quality.

In the five most recent tanks on 91 octane, that hill (and a few others) that forced an automatic downshift with 87 octane have consistantly NOT forced the transmission to downshift.

Conclusion: Since the ECU retards the timing the most during low RPM/high load conditions, therefore reducing the inherent ping from running 87 octane with a 10.5 compression ratio, and since 91 octane is capable of running without pinging at more advanced timing, the ECU is not retarding the timing as much in low RPM/high load conditions, producing more power.

This is adequately supported by the automatic transmission remaining in 4th gear (locked) at a constant 35MPH up hill rather than consistantly shifting down to 3rd gear (locked) because of inadequate power production from the engine at low RPM/high load.

What makes this a much less subjective test than the usual 'butt dyno' is that the electronic brains are determining all changable parameters except for throttle position required to maintain 35MPH on the hill.

This was thoroughly discussed in the thread I linked to above.

This is the second time I've gone from 87 to 91 octane fuel, and the same effect was readily observable both times - and the last time, when I went back to 87 for verification, the vehicle again was forced to shift to a lower gear on that hill.

This is exactly the sort of result that should be expected from a high compression engine (yes, 10.5:1 IS high compression) with an ECU designed to control valve and ignition timing to allow running on 87 octane fuel.

This is one reason the ECU has multiple control tables (advance/retard/overlap) with multiple curves to use - some fuels do not require as much manipulation of timing as others to prevent ping, and can put out more power at relatively low RPM/high load conditions.

All that being said, the difference in MPG, if there is one, is totally buried in the expected measurement errors/driving differences of everyday use.

Tomas

 

i run a bottle of lucas oil fuel injector cleaner once a month, it cant hurt, but i dont think it does anything noticable, but if you run a good quality gas you should be ok.

also all this talk of cheap gas, think about it; what is the actual difference between 2.99 and 3.20 per gallon, not a huge amount, IMO buy the better gas.

also those chemical flushes that someone was talking about, i did that with my chevy and noticed a huge difference, i flushed the tranny and the motor. and that was like at 50k

 

Hmmm very interesting topic. I am currently trying out 91 octane gas.

I live in a private valley with many hills to climb to get to my own home.

Now I used to accelerate using 3rd gear. 4th was a no go as i would lose power going up the hill.

But after switching to 91 and resetting the ECU after the 3rd tank full. Mind that i filled up when the gas light was on. I can easily hold 4th gear at 30mph and it will accelerate (slowly) ... Now it seems that Tomas is right in saying that the ECU is not retarding the timing.

The car doesn't accelerate any differently on flat surfaces but when i'm cruising , shifting at 3k and trying to get the most MPG... i think it makes a difference. But to each their own.

 

Close, but the ECU is probably still retarding the timing, just not as much, when running 91 or 93 octane fuel.

10.5:1 used to require 100 octane or better when properly tuned, but that was in the days of mechanical advance distributors, etc.

Now that ECUs can 'listen' to the engine and keep it out of trouble by retarding the timing, we can get by on lower octane fuels, and not even notice except at the performance extremes.

*PING!* Oh! Just remembered something!

Everyone remember the reduction in advertised horsepower and torque for our engine last year? Remember why the numbers changed but the actual engine output in everyday use did not (zero changes to the engine)?

Don't remember why?

I seem to recall part of the reason was a change in the testing procedures that required manufacturers to use their recommended octane istead of higher octane fuels during the test.

Now I'm going to have to find the press releases for that change, and the explanations given. :D

Tomas

 

Yup. I remembered correctly. The '05s were tested using premium fuel and the '06 and newer using the 'recommended' fuel, thus the reduction in advertised torque and horsepower. :D

 

I didn't think of that. Now that I have been running 93 for several tanks, I need to let the engine optimize its advance curves.
https://www.scionlife.com/forums/viewtopic.php?t=33062

That's what I think, too.

 

Bingo, bingo!

 

Bingo, bingo! It's the same reason the manual recommends 5k oil changes and never changing the transmission oil.

 

Increased octane has absolutely zero affect on performance and cleanliness of the engine. Unless you are running a higher compression it will not help MPG or anything. The higher octane is to just deter premature detonation.

Do a google search and you will find about 200,000 articles supporting this:

Are you tempted to buy a high-octane gasoline for your car because you want to improve its performance? If so, take note: the recommended gasoline for most cars is regular octane. In fact, in most cases, using a higher octane gasoline than your owner’s manual recommends offers absolutely no benefit. It won’t make your car perform better, go faster, get better mileage or run cleaner. Your best bet: listen to your owner’s manual.

http://autorepair.about.com/od/gener.../aa060504a.htm
More info this time from the federal trade commision:

http://www.ftc.gov/bcp/conline/pubs/autos/octane.htm

The Low-Down on High Octane Gasoline
Are you tempted to buy a high octane gasoline for your car because you want to improve its performance? If so, take note: the recommended gasoline for most cars is regular octane. In fact, in most cases, using a higher octane gasoline than your owner's manual recommends offers absolutely no benefit. It won't make your car perform better, go faster, get better mileage or run cleaner. Your best bet: listen to your owner's manual.

The only time you might need to switch to a higher octane level is if your car engine knocks when you use the recommended fuel. This happens to a small percentage of cars.

Unless your engine is knocking, buying higher octane gasoline is a waste of money, too. Premium gas costs 15 to 20 cents per gallon more than regular. That can add up to $100 or more a year in extra costs. Studies indicate that altogether, drivers may be spending hundreds of millions of dollars each year for higher octane gas than they need.

What are octane ratings?
Octane ratings measure a gasoline's ability to resist engine knock, a rattling or pinging sound that results from premature ignition of the compressed fuel-air mixture in one or more cylinders. Most gas stations offer three octane grades: regular (usually 87 octane), mid-grade (usually 89 octane) and premium (usually 92 or 93). The ratings must be posted on bright yellow stickers on each gasoline pump.

What's the right octane level for your car?
Check your owner's manual to determine the right octane level for your car. Regular octane is recommended for most cars. However, some cars with high compression engines, like sports cars and certain luxury cars, need mid-grade or premium gasoline to prevent knock.

How can you tell if you're using the right octane level? Listen to your car's engine. If it doesn't knock when you use the recommended octane, you're using the right grade of gasoline.

Will higher octane gasoline clean your engine better?
As a rule, high octane gasoline does not outperform regular octane in preventing engine deposits from forming, in removing them, or in cleaning your car's engine. In fact, the U.S. Environmental Protection Agency requires that all octane grades of all brands of gasoline contain engine cleaning detergent additives to protect against the build-up of harmful levels of engine deposits during the expected life of your car.

Should you ever switch to a higher octane gasoline?
A few car engines may knock or ping - even if you use the recommended octane. If this happens, try switching to the next highest octane grade. In many cases, switching to the mid-grade or premium-grade gasoline will eliminate the knock. If the knocking or pinging continues after one or two fill-ups, you may need a tune-up or some other repair. After that work is done, go back to the lowest octane grade at which your engine runs without knocking.

Is knocking harmful?
Occasional light knocking or pinging won't harm your engine, and doesn't indicate a need for higher octane. But don't ignore severe knocking. A heavy or persistent knock can lead to engine damage.

Is all "premium" or "regular" gasoline the same?
The octane rating of gasoline marked "premium" or "regular" is not consistent across the country. One state may require a minimum octane rating of 92 for all premium gasoline, while another may allow 90 octane to be called premium. To make sure you know what you're buying, check the octane rating on the yellow sticker on the gas pump instead of relying on the name "premium" or "regular."

 

OK, now that we have waded through THAT out-of-date steaming pile of, uh, rubbish, here's a bit of data about OUR SPECIFIC VEHICLES that makes that information incorrect.

(1) Our engines should not ping on 87 octane fuel because the ECU and it's knock-sensor just won't let it. The ECU will progressively retard (de-tune) the engine until it detects no incipient pinging/knocking, and even increase the intake/exhaust valve overlap to effectively reduce the compression ratio if retarding the timing to the limit won't do the job.

(2) While increasing the octane rating of the fuel in a STATICLY TUNED ENGINE will not increase it's power output, doing the same in a DYNAMICLY TUNED ENGINE can keep the ECU from REDUCING engine power output under high load to prevent pinging/knocking.

(3) This one I want to address in some detail:

Toyota, along with three other vehicle manufacturers have stated, repeatedly and in writing, that the current EPA required levels of detergents in gasolines is insufficient, and even offered up validated test results SHOWING the results supporting this.

That is why Toyota, along with three other manufacturers, came up with the "Top Tier" validation system for gasolines, and require third-party testing of gasolines to qualify for Top Tier status.

Toyota recommends that all of their vehicles in the US use only Top Tier gasolines.

While ALL grades of gasoline sold in the US supposedly meet the minimum EPA detergent requirements, Toyota's testing has shown that the quantity and quality of those detergents is NOT enough to prevent damaging deposits. Some fuel providers DO put more detergents in their higher grade fuels than in their lower grades. This means that the more expensive, higher grade, higher octane fuels from non-top-tier providers MAY have more adequate detergent levels than the minimum EPA requirements, but there is no guarantee.

If Top Tier gasolines are available in your area USE THEM. It is a false economy to save a few cents on the gasoline if the gasoline will eventually cause damage.

If Top Tier gasolines are NOT available in your area, you might want to consider a higher octane fuel as your choice, NOT because of the higher octane, but because of the likelyhood of having more and better additives may save your engine from problems.

There are so many other errors, omissions, and just plain quarter century out-of-date items in that quoted FTC tract, that it is mostly more wrong than right for OUR cars.

I'll trust the manufacturer that can engineer and tweak a tiny, high compression engine to run on 87 octane fuel without damage one whole heck of a lot more that some overly generalized, out of date, self-serving, misleading, drivel from an anonymous pack of federal bureaucrats.

Tomas

 

The effect of compression ratio as a determining factor as to what fuel an engine with electronic closed loop management requires is completely outdated. I have an 06 Yamaha FZ6 that has 12.4 :1 compression ratio and a 14,000 RPM redline. It cruises at about 8,500 RPM and on most Sunday mornings, it cruises at about 11,500 RPM. (for a few hundred miles) The manual calls for 87 octane. I run 87 octane. No problems. The Xb gets 87 octane too. I use Chevron. I don't need much performance out of the Xb as I fulfill that need otherwise. But as far as this discussion goes, If you truly understand the Xbs fuel management and engine control systems, the use of higher octane fuel will allow more ignition timing, and as we all know, this has the potential to make more power. How much more??? Good question, I don't know. I don't really notice it because I'm not really looking for it. Some may. The real question is: Does the cost difference justify the mileage???? Maybe Tomas will let us know. If you just drive your car normally and are a cheap bastage like me, 87 is perfect. If you want to use higher octane-fine, no problem. Kinda like mayo or mustard- either one will really do. One thing to note is that in colder weather high-octane fuels are harder to get lit so starting may take a few more spins. Now fuel quality on the other hand, is a much more worthy topic! Top-Tier fuels are the way to go!!!! Fuel deposits on the back of intake valves start out as gums and resins and over time harden and burn further and become carbon. Carbon is an excellent absorber of hydrocarbons ( thats why a charcoal cannister is used to store fuel tank vapors). If the back side of the intake valves are coated with a substance that is absorbing the other substance you are trying to get past them, drivability problems are headed your way. Early high-milage Tercel engines suffered from this problem to the point where they would refuse to start. The cost to repair was usually more than the car was worth, relagating them to the Bic Lighter of cars status. Moral of this story: Use whatever the hell HIGH QUALITY fuel you like. (and listen to Tomas!)

 

To answer Scott's question, just compare the higher 2005 horsepower and torque figures to the lower 2006 figures.

 

Looks like the easiest way to pick up 5 HP is to use premium gas:

2005 xB on premium gas
108 hp @ 6000 rpm
105 ft-lb @ 4200 rpm
http://www.automotive.com/2005/12/sc...ons/index.html

2006 xB on regular gas
103 hp @ 6000 rpm
101 ft-lb @ 4200 rpm
http://www.automotive.com/2006/12/sc...ons/index.html

 

I do believe there were other factors to consider with the new testing standards.

 

As for cost difference, I just filled up my tank with 91 octane and it was a whopping $1.80 more compared to 87 octane for 9 gallons. I think that's worth it for more detergents and more horsepower.

 

Why do you say "believe"? Could a change from premium to regular not account for 5 hp?
What other factors would it take, in addition to changing the gas, to account for 5 hp?

 

If I remember correctly, the HP testing included all items "as installed" such as drive belts and alternator drag and such. I'm too tired to look it up but you could easily search for the new testing parameters.

 

According to the information released, the engines were not changed from stock for the 2005 and earlier testing, and the only differences were the use of premium fuel and the more advanced timing that allowed. For 2006 and later, factory recommended lubricants, 87 octane fuel, and the timing required by that fuel, were the only difference from earlier tests... Scions WERE "SAE Net" and became "SAE Certified."

(The only question still left is if they advanced the timing more than the stock ECU curves allowed prior to 2006 - Toyota hasn't said one way or the other on that.)

This is the third time in MY memory that the SAE parameters have been changed as to what can be advertised.

I remember SAE Gross HP - that was a bare naked engine with no fuel pump, oil pump, water pump, generator, air filter, muffler, or any other 'power drains' being attached to the engine. All those extra goodies were separated from the engine.

That eventually was changed to SAE Net HP, where the manufacturers were required to hook up all those 'extras' that were normally installed on the engine, so that the engine was run self-supported instead of requiring external pumps and such.

Now they've tightened it down again, requiring not only those 'extras' be attached and powered by the engine, just as they would be in a customer's car, but requiring that they be tested with the manufacturer's recommended fuel, oil, and coolant, and that no special tuning be allowed. The engines are supposed to be "as delivered to the customer in the vehicle" from the factory. That's SAE Certified HP - the rating we see now.

I'm certain there are a lot of other holes plugged each time the 'rules' change, but that's the biggies for the last three that *I* recall. (I do vaguely recall SAE Estimated HP being used, where the maximum theoretical power that could be extracted from an engine of that displacement was used for advertising, but that was before I really started to pay attention.)

I still prefer the power rating Rolls Royce used on its cars for years and years: "Adequate." :D

Tom