Originally Posted by gslippy

Too bad you and some others see fit to resort to insults in a forum where we are just trying to be helpful to one another.

You'll note that I never said that you'd realize any great gains from running higher octane fuel. You'll also note that I never said you NEED anything better than 87 octane. However, you WILL realize more power from an engine fitted with a knock sensor AND running higher octane fuel than one without those things.

The shop manual states that "During Fail-Safe mode, the ignition timing is retarded to maximum retardation". Perhaps you've never set the ignition timing on an engine, or understand how to actually improve power in an engine, but the purpose of the knock sensor is to maximize power in the engine with the fuel it is given, without permitting it to knock. Knock is extremely destructive to an engine.

Toyota didn't fit these engines with knock sensors just for fun. It's there so that you can get every bit of power the engine has to offer without destroying itself. Many manufacturers list their horsepower based upon using premium fuel. Such engines have knock sensors. Toyota has chosen to rate this engine at 108 HP on 87 octane. This engine with a faulty knock sensor will still develop 108 HP on 87 octane, and nothing more with 93 octane. But this engine should develop more power (how much, I don't know, but maybe 5 HP), if running on higher octane gas with a functioning knock sensor. If Toyota just wanted this engine to never knock, they could have retarded the basic timing curve to a very conservative setting, but instead they wanted it to develop some usable power for this application without the need for premium fuel all the time.

Of course this isn't a big-block with 11:1 compression. I'm just explaining the fundamentals of engine performance as it relates to fuel octane and knock sensors. Whether you want to spend the extra 20 cents on premium gas for a few extra HP is up to you. Such fuel may also get you better fuel economy because the power output is up for a given fuel delivery rate. Again, the tradeoff is up to you.

As I said in my prior post, I'd be surprised if any 1.5L has knocked on any octane fuel, because of the knock sensor. The only time you prevent knocking with higher octane gas is on a vehicle NOT fitted with a knock sensor, and whose ignition timing is overly advanced for 87 octane. So if you prefer to limit the engine to 108 HP on 87 octane and save your money, that's your choice.

As McBain said above, the knock sensor lets the engine run at peak efficiency just under the knock threshold. Peak efficiency means peak HP for the given load, because you're wasting less energy and gaining maximum power, which is the definition of efficiency.

Have any of you run this engine on a dynamometer to prove that high octane fuel is worthless in this engine?

Originally Posted by jethro b

Spend all you want on gas. I don't really care Just stop telling other people that there is a benefit to burning premium when there really isn't. Remember if people hear enough BULL$HIT they start to believe it. I can't help that 20 percent of the people in the poll are flushing money down the drain and making the oil companies richer. Some have more money than they know what to do with.

Originally Posted by Chikubi

I would suggest before calling BULL$HIT on people to do a little research so you know what you're talking about -- to quote Shell Canada's website (http://www.shell.ca/code/motoring/tips/gasoline.html):

"Engines in vehicles built for sale in North America are designed to a specified octane requirement to make sure they don't knock or ping (engine knocking reduces the amount of power it can deliver to turn the wheels). Once that octane level has been met, in normal instances your car will not experience more power or better mileage if you use a higher octane fuel.

In other words, if your Canadian vehicle owner's manual specifies an octane rating of 87, running on gasoline with an octane rating of 89 or 91 or more will normally not make a difference.

However, there are some exceptions to this, and it must be noted that if the owner’s manual specifies using gasoline with an octane rating of 89 or 91, then that’s what you should use because that’s what the engine is designed and tuned for.

One - and a very important - exception is that when a vehicle gets older, the normal build-up of fuel- and lubricant-related deposits in the engine can increase the fuel octane number a car requires to prevent engine knock. For this reason, if a car more than a couple of years old experiences engine knocking, the problem may be solved simply by moving to the gasoline with the next-higher anti-knock index.

You will also benefit from a higher octane rating if:

the engine is knocking on the gasoline you are using, or

you have knock sensor ignition that can take advantage of higher octane values at times of peak demand, or

high summer temperatures, mountain driving, pulling heavy loads (including loaded roof racks) has temporarily increased your engine’s anti-knock index requirements.

While fuel with a higher octane rating cannot of itself deliver more power, in the above circumstances it can give an engine a greater ability to resist knocking, thereby helping it to deliver the full measure of power it is designed and tuned to provide.

In these cases, where drivers require their vehicles to continue providing peak performance despite challenging driving conditions, for improved responsiveness we recommend using a mid-grade fuel like Shell Silver (octane rating 89) or a premium fuel like Shell Optimax Gold (octane rating 91) gasolines.

One other exception is found in high-performance vehicles. The use of more complex computer algorithms in their engine control systems to control spark timing using one or more knock sensors, enables better performance on higher-octane fuel. Owner’s Manuals for most of these vehicles will specify use of 91 octane fuel."

So while you're right that the octane rating in and of itself in normal circumstances won't provide an improvement when using higher octane gas in a vehicle, there are a number of exceptions where there is an improvement (gslippy's knock sensor equipped engines example being one). Laugh all you want, but you're wrong, and I can tell you flat out that here in PA where we got long, steep ___ hills, there most definitely is a noticeable difference between 87 and 93 oct when climbing them. You can argue all you want, but you're not gonna one-up a company that makes gasoline.