What grade of gas do you pump?

[priusenvy]

Originally posted by Gen2@Mar 22 2006, 04:12 PM
Although Toyota does state in their documentation that the compression ration is 13:1, the valves are held open well past the point where they would close on a normal Otto cycle engine so the net result is that you actually only get 8.0:1 compression ratio (which is also decumented by Toyota). The head design is the same as other Toyotas, its the VVTi engine control program that performs that little timing trick, which converts the engine from Otto cycle into an Atkinson cycle engine. The expansion ratio does stay at 13:1 which is where the efficiency comes in.

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I've seen the numbers 13.5:1 for expansion ratio, and 9.5:1 for effective compression ratio mentioned in several online sources. In fact, I've seen them enough times that I'm inclined to believe that they are the correct figures, not the 13:1 and 8:1 that you listed.

My Acura MDX was designed for premium fuel, but the ECU can retard the timing to prevent pinging when you put regular in it. I get about 10% better fuel economy on premium (due to the timing advance), so as long as premium is less than 10% more expensive than regular (as it is now), I put premium in it. Most cars that were designed for premium, but which can run on regular behave similarly to this.

[Andy Ling]

Hi Guys!

I use 87 only cos it's what the manual sez. Also, I bought the car coz it runs on 87 which is the cheapest.
This topic is crazy. We are mostly tight-wads, anyway. Why bother.
I will bet if there was 80 at a lower price, and the Prius manual says to use it,
y'all will use it!! Trust your Toyota maker!!

[Andy Ling]

Originally posted by coolfire74@Mar 18 2006, 02:53 AM
Always 87 octane from Shell, because 87 is the cheapest, and a shell gas station locates very close to my home. But I may consider the V-power from shell every 6 month, some people believe that V-power can help cleaning your engine. Is it true? I do not know, but worth trying every couple of months, I guess.

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That's hog wash!!
Keep your motor oil changed every three months. That's what keeps the motor clean!! Don't be ripped off!!

Andy

[finman]

"Humm.. I believe the prius has a high compression ratio... what is it?... 12:1 or so?
Yet I've heard it does not better.... of course the atkinson engine is a whole different animal. "

I want to say the Atkinson cycle has a high-expansion ratio, not high compression ratio. I'm actually not sure what that should mean but I'm sure someone here can comment...

[galaxee]

Originally posted by joeh4@Mar 24 2006, 04:02 AM
No, actually I'm along the Wisconsin/Illinois border.  There are about 6 gas stations within 1.5 miles of where I live.  All but 2 have 89 for regular and only Shell and Phillips 66 are "Top Tier" as recommended on www.toptiergas.com/retailers.html.  Mobil has 87 octane but from what I read a few years ago their regular is not the quality of Shell, Phillips 66 and others.  Their higher grades do have better detergents as I remember from about 5 years ago.  The "Top Tier" article doesn't list Mobil or any other around my area such as Chevron, Texaco, 76, etc..

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strange. are you on the WI or IL side of the border?

i'm actually from WI, and i've never seen 89 as regular. maybe it's an IL thing? or they've changed things since i've been home? (argh, i've been gone too long)

i know kwik trip a few years back decided to price regular and midgrade the same, when i lived in la crosse. maybe that had something to do with it? ah, now i'm just blathering.

i wouldn't worry too much, no need to go to extremes here. it's not like you're dropping 93 in there right?

if you do get one of those "engine failed to start" codes after long term use (can be caused by high octane), then i'd consider going a little farther to get 87.

[richard schumacher]

Originally posted by rposton@Mar 22 2006, 10:17 PM
I think aviation gas for piston airplanes is even higher octane than what is sold for cars.  If so, then they burn a, "...lower the energy in the fuel..." type of fuel?  I thought that they needed all the performance that they could get without adding the weight of a bigger engine.

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Just as you wrote, "performance" in an airplane means more power per engine mass. For a piston engine this requires the highest possible compression ratio, which requires fuel with (ta da!) a very high octane rating. The slightly lower energy density of that fuel is not very significant.

[tripp]

I'm now using 85 octane with no noticable penalty of any kind. I'm half way through my second tank. Woohoo, I can save an extra $1 at the pump.

Richard, that's interesting. I read somewhere that Snaab or Volvo was developing an engine to run on E85 that had very high compression ratios to compensate for the lower energy density of E85 vs Gasoline.

[windstrings]

<div class='quotetop'>QUOTE(tripp @ Apr 24 2006, 08:15 PM) [snapback]244669[/snapback]</div>

I'm now using 85 octane with no noticable penalty of any kind. I'm half way through my second tank. Woohoo, I can save an extra $1 at the pump.

Richard, that's interesting. I read somewhere that Snaab or Volvo was developing an engine to run on E85 that had very high compression ratios to compensate for the lower energy density of E85 vs Gasoline.
[/b]

Say tripp.. does that have even more ethanol than 87?... if so, are you getting worse mileage and so not really saving a buck?