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Discussion Starter #1
was filling up the 16.3 gallon tank on my current car with 93 octane this evening... 300 miles for 16 gallons = less than 20 mpg... plus Super is always at least 20 cents more...

got me thinking... what is Toyota's "recommended" fuel for the Prius?? I saw that the new engine will be 13:1 static compression ratio and depending on valve timing this is extremely high.

My 325 calls for 91 plus and is only 10.5:1...
A friends S2000 calls for 91 and is 11:1...

(for everyone's info, there is absolutely no more energy per volume of gas for a higher octane, this "rating" is a ratio or percentage of 8 carbon gas to non-8 carbon gases (heptane and lower) - more power CAN BE EXTRACTED from a higher octane because it is MORE STABLE)
 

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The manual says 85. The tank size is 11.6 gal (typical fill up will be 10.5 gal). Range (with that 10.5 gal) is 470 at the average 45 MPG I get. You will find that many people at this site get better fuel economy than I do. In any case, assuming you filled both cars with 10.5 gal, you would go 273.13 miles further and pocket $2.10 with the current generation prius. The 2004 prius will get 55 MPG average.

> I saw that the new engine will be 13:1 static compression ratio.

I hope they don't change it on us.

Aron
 

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re: octane required

Toyota recommends 87 octane, and no more. There are entries on this board that advise against any higher octane.
 

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87 octane!

from pages 144-145 of my old 2001 manual:

"OCTANE RATING
Select unleaded gasoline with an Octane Rating of 87 (Research Octane Number
91) or higher."

Quality gasoline, gasoline with detergent additives, and low sulfur gasoline
are all preferred.

MMT (Methylcyclopentadienyl Manganese Tricarbonyl) additives is not
recommended.

"OXYGENATES IN GASOLINE
Toyota allows the use of oxygenate blended gasoline where the oxygenate content
is up to 10% ethanol or 15% MTBE. If you use gasohol in your Toyota, be sure
that it has an octane rating no lower than 87.
Toyota does not recomment the use of gasoline containing methanol."

Also note not to spill gasohol when refueling, as it'll eat the paint.

Just to note, there have been several
reports of "Check Engine" lights attributed
to using gasoline with an octane higher than
87 (most common reports with 93).

Basically, the Prius
is designed for 87, and many people report lowered MPG (higher octane has less
energy (BTUs) than lower octane) when driving with "Premium" gas. You'd be
wasting money and MPG if you use something higher than the "Regular" 87 octane.

(However, if you're living in, say, the Rockies (like Denver or another HIGH
altitude place), you can get away with 85 octane...)

I will note that the FTC has this
report about the common misconceptions
about high-octane ("premium") fuel use
in cars that don't require the high
octane fuel:
http://www.ftc.gov/bcp/conline/pubs/autos/octane.htm

some more info is also here:
http://www.ftc.gov/bcp/conline/pubs/alerts/fuelalrt.htm
 

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Re: I saw that the new engine will be 13:1 static compression ratio and depending on valve timing this is extremely high.

Hmm, are they still reporting that wrong? The expansion ratio is 13:1, the effective compression ratio is never anywhere near that high. The compression ratio is less than 9:1, sometimes much less. That's the atkinson cycle engine for you. It's why you get such high efficiency from an engine that can run on 87 octane.
 

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Discussion Starter #6
is it really wrong??

Static compression has a definitive way of being calculate...

initial cylinder volume / final cylinder volume = ratio

I totally understand the volumetric inefficiency and valve timing will ultimately control the true compression ratio.
 

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Ok, by that definition, "static compression" has absolutely nothing to do with octane requirements. So why say its "extremely high"?
 
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