why 91 octane in the prius?

There was some confusion with my wife, RE octane. She initially thought 91 octane was required. She was reading "Research Octane Number 91"

From the 08 Manual Page 472 (Excerpt)

"Premium unleaded with an Octane Rating 87 (Research Octane Number 91) or higher is required for optimum engine performance.

If your engine knocks:

Consult your Toyota dealer

You may occasionally notice light knocking for a short time while accelerating or driving uphill.
This is normal and there is no need for concern."

We are using 87 octane, and as long as the engine does not knock (or ping), there should be no problems.

 

yes, if that is what they say use, then they have adjusted the maps in the ecu (timing etc,) to work with that gas.

 

i know someone from hong kong who says its common there for people to idle their cars for 10 minutes to "warm it up" before leaving their 75-degree indoor parking garage.
I told him his people were brainwashed by the oil companies to waste more oil and make the oil companies richer. in fact idling is very damaging to engines cause it doesn't put a load on the engine which is what it is designed for, even in the coldest of winters you are supposed to get in the car, start it up and go immediately.
that isn't to say that engine block heaters aren't a good idea and very helpful, just don't let it run the whole night, let a timer turn it on 3 hours before you plan on leaving for work.
and never ever put a remote starter on any car, you'll ruin the engine.

 

I don't quite know if I agree with this. Most manufactures are starting to install remote start as a standard item. They are timed to run for 10 minutes and then shut off.

Using a remote starter to warm your engine up will never ruin a gasoline engine. If this was the case, major auto manufactures like GM, Ford and others would be setting themselves up for MASSIVE recall issues etc...

 

funny thing is i now for a fact that when you drive a older car you need to run the engine hot before realy putting down the trottle!
because you can and will damage the engine!
and i now that for a fact because i have seen it happen!

 

This is the most accurate answer out of the bunch... the rest... Well, I would think you guys can become witchdoctors anytime now...

There is only 1 clarification needed: Your gasoline is not made up of 87% Iso-Octane and 13% Heptane... It is a blend of various hydrocarbons which have the equivalent knock property of the Iso-Octane / Heptane mixture using an ASTM test proceedure (which has absolutely nothing to do with the Prius engine - It is just a laboratory proceedure.)

I would recommend 2 good web sites to help clarify what is going on with your gasoline and your engine.

First: Chevron's official web site talking about Octane and Knocking.

Chevron Products: Mr. Gasoline Search Results

Second: A very nice article that explains in more technical terms the various attributes of a fuel and how they relate to engine performance.

Octane determination in Piston Engines

If the above is way more information then you wanted, then let's just say that your Prius runs absolutely fine with the lowest grade of gasoline available in the USA or Canada.... and anything else is just a waste of money.

 

lol, you are right of course, but i figured i would break it down simple instead of getting to much into the breakdown of hydocarbons and alternitives to the two i listed .

im off to read the links you gave!

 

They are putting them in as 'convenience features' not because they are needed. As Click and Clack have said for years, the engine will warm up faster if you DRIVE it.

I would prefer they be illegal (and I had one on my '95 Honda Odyssey). Sure, it is nice that you don't have to bundle up to start it then go back inside for a few minutes on those really cold days (i.e. -20F) that you need to let the (non Prius) vehicle warm up before it is drivable. BUT it is TOO easy. At temps when the car will start and run fine immediately, hey why not start it early anyway so you will have full heat when you get in? Just a minute or two, or 5 or 10 when you don't get out as fast as you thought you would. I know people that use their remote starters when the car has been run for 30 minutes, then stopped for an hour and it is 40F. These same people will stand in a ski lift line for 30 minutes, then sit on a chair lift for 10 minutes at 0F plus wind. But they 'need' instant heat in their car in their regular daily routine.

BTW, in Burlington, VT, it is illegal to idle for more than 5 minutes (not that anyone cares).

 

I'm not sure on the octane thing. Isn't it true that the Continuously Variable Transmission on the Prius causes the engine to always open at full open throttle?
Continuously variable transmission - Wikipedia, the free encyclopedia
And that full open throttle is when higher octane gas helps out with efficiency?
Fuel economy-maximizing behaviors - Wikipedia, the free encyclopedia
Also, there's a study from Toyota (not Prius specific) that showed higher octane could lead to higher efficiency:
"This paper investigates the impact of high RON fuels on the thermal efficiency by using high compression ratio engine, turbocharged engine, and lean-boosted engine. Finally, it is shown that the high thermal efficiency can be approached with high RON gasoline and ethanol. "
The Impact of RON on SI Engine Thermal Efficiency
In any case I think it's not a bad idea to put in 91 every 5th tank or something, if only to get the additives that help clean your engine. I had a Toyota Sienna that had to have it's spark plugs replaced at 75k at a cost of like $900 (labor intensive) - wish I had kept those spark plugs cleaner!
It might be cheaper to actually just buy the additive and put it in yourself though...

 

Those engine properties (high compression ratio, blower, lean boost) are the ones that would make an engine capable of getting a significant benefit from higher octane fuel - but those are not properties of the Prius engine.

ISTR there was a Consumer Reports article about a dozen years ago about the octane question, where they did say that some refiners reserve their best detergent blends for their 'premium' offerings, but also that there were some that used the same additive blends across their range of octane numbers. The article had a list of the brands where you could buy the 87 fuel and still be getting the same additive package as in the premium. I remember at the time Phillips 66 was one of them, and I used those stations by preference for several years, until all of them in my neck of the woods were bought out by other brands.

Did you say $900 labor for spark plugs?

-Chap

 

> $900 for spark plugs?
It was exorbitant. That included parts and labor (oops, and a 'system flush' and tune up).
Apparently they are REALLY HARD TO GET TO - another shop (not the dealer) quoted me MORE.
Replace spark plugs on 2003 sienna - Tundra Solutions Forum
I also just had to replace the whole A/C system at a cost of over $1,300.
I know this is a bit off topic but what did I learn - get the 100k warranty! Even though Toyotas are supposed to be reliable... I've spent about $3k for repairs on that 2005 Sienna so far (and yes, I bought it brand spanking new).

 

It is not true that the CVT causes the engine to always open on full throttle. And it is not true that full throttle benefits from higher octane.

The engine in the Prius can operate at high rpm when the car is moving slowly, due to the unique drive train, which is not really a CVT at all, but rather a power split device. But it only does this when the computer wants a lot of power from the engine.

Octane is not a measure of the quality of gas. It is a measure of the ignition temperature. High compression engines create higher internal temperatures, and can cause the fuel mixture to ignite before the spark fires. This is bad. High-octane gas will not do this. But in a low-compression engine, high octane gas has absolutely no benefit whatsoever! It does have less energy and higher cost, so you pay more to go fewer miles.

Use only the recommended octane gas!

 

Well, to be fair, physicsdude really wasn't that far off.

Yes, the Prius powertrain uses a Power-Split Device. It is also a transmission that can couple engine power from anywhere on the speed-torque curve to the drive axles, not at a choice of fixed ratios but anywhere else on a speed-torque curve between upper and lower limits ... which is what makes it a CVT.

And that does allow the hybrid-vehicle ECU to use a control strategy where the throttle is usually open wider than you'd expect, and the engine's power output is modulated more by using an effective high or overdrive transmission ratio to hold the engine down to a desired spot on its rpm-power curve, instead of taking the efficiency hit of sucking air past a partly closed throttle. Because the ECUs have
simultaneous control over the throttle, effective CVT ratio, injection, ignition, and intake valve timing, they can work that strategy pretty well.

Of course it's still the case that the car's designed for 87 fuel and can use it without any preignition problems.

-Chap

 

While Premium does not have any more energy it doesn't have any less energy either, does it?