- #212 of 281
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Re: in cars designed for 91 max, does 92,93,94 help anything? [shipo]
by Mr_Shiftright HOST
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May 09, 2006 (9:10 am)
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Replying to: shipo (May 09, 2006 8:50 am)
Yeah, true, but with the engine loafing at 2,000 rpm the spark isn't going to need to advance...there's really no demand on the engine whatsoever. It is hardly working. It should run great on really cruddy gas under those conditions seems to me. I can't see why the knock sensor would even be operating.
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- #213 of 281
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Re: in cars designed for 91 max, does 92,93,94 help anything? [Mr_Shiftright]
by shipo
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May 09, 2006 (9:16 am)
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Replying to: Mr_Shiftright (May 09, 2006 9:10 am)
"Need" isn't the issue, fuel economy is. Think about it, even my 1966 Plymouth Valiant with the 225 Slant Six was equipped with a vacuum spark advance for steady speed low power cruising. That system used zero detonation detection and as such had to be extremely conservative. With the advent of all of our modern engine controls there is absolutely no reason that the ignition timing cannot be advanced to the point of detonation (and then backed off a hair) even under the lowest power driving environments.
The simple truth is that the further the ignition timing is advanced (shy of detonation), the better the fuel economy an engine will return. Why? The primary reason is thermal efficiency, retard the timing, the peak combustion temperature (and peak cylinder pressure) drops, advance the timing and the peak combustion temperature (and pressure) rises. The more heat extracted from the fuel, the more work the engine is capable of performing for any given amount of fuel.
Best Regards,
Shipo
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- #214 of 281
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Re: in cars designed for 91 max, does 92,93,94 help anything? [elias]
by wai
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May 09, 2006 (9:35 am)
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Replying to: elias (May 09, 2006 6:08 am)
I have experimented my Jetta VR6 with 91 octane the previous month due to high gas price instead of 93 octane which I used from the new car till now (18,000 miles). I actually get better performance with 91 octane, quiet engine, nice pick up at freeway or during aggressive accelaration and mileage is more or less the same.
The result might be different if this is a Winter season.
My Jetta required min. 91 Octane. But its more time consuming in pumping the gas as most gas stations don't have 91 octane gas, I have to mix it up myself. I suggest you to use 91 octane to save some money.
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- #215 of 281
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Re: Quality and brand names? [another_bill]
by rbirns1
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May 09, 2006 (9:48 am)
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Replying to: another_bill (Apr 19, 2006 3:16 pm)
Hess makes very good quality gasoline. I've been using Hess for many years in several different cars with no problems or disappointment at all. They are consistently cheaper than the other major brands because they own all the stations directly. They also have a well earned reputation for the cleanest stations anywhere. Leon Hess was legendary for that. He owned the New York Jets and moved them out of Shea Stadium because the bathrooms weren't up to his standards. It's true.
Anyway, go ahead and fill up at Hess. The only difference you'll notice is the extra weight in your wallet.
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- #216 of 281
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Re: in cars designed for 91 max, does 92,93,94 help anything? [wai]
by shipo
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May 09, 2006 (10:22 am)
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Replying to: wai (May 09, 2006 9:35 am)
What is true for one engine isn't necessarily true for another. While your VR6 may not be able to take advantage of the extra detonation resistance of the 93 (in the form of an advanced spark), other engines are designed and built to do just that. As such it is wise to evaluate what is the best fuel grade on a case by case basis.
Best Regards,
Shipo
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- #217 of 281
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Re: in cars designed for 91 max, does 92,93,94 help anything? [Mr_Shiftrigh [elias]
by wai
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May 09, 2006 (11:13 am)
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Replying to: elias (May 09, 2006 8:41 am)
What is the fuel door or manual stipulated Octane required?
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- #218 of 281
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Re: in cars designed for 91 max, does 92,93,94 help anything? [wai]
by elias
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May 09, 2006 (12:08 pm)
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Replying to: wai (May 09, 2006 11:13 am)
owners manual of my 05 goat recommends 91+ octane...
i'll try to remember to read the exact text and will post more later if that's not accurate.
i know the inside of fuel door just says "premium fuel recommended".
does the owners manual of *any* USA car recommend gasoline octane *larger* than 91? !?
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- #219 of 281
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Re: in cars designed for 91 max, does 92,93,94 help anything? [shipo]
by Mr_Shiftright HOST
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May 09, 2006 (12:18 pm)
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Replying to: shipo (May 09, 2006 9:16 am)
It's my present understanding that using 91 octane in a car designed expressly for 87 octane is pretty much a waste of money, unless you want to factor in perhaps a slight benefit from additives. This is what the engineers seem to tell the consumer.
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- #220 of 281
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Re: in cars designed for 91 max, does 92,93,94 help anything? [Mr_Shiftrigh
by elias
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May 09, 2006 (12:23 pm)
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Replying to: Mr_Shiftright (May 09, 2006 12:18 pm)
Mr. Shiftright, i recall that a few years ago some law/policy/thingy passed requiring the oil companies to put the same additives/cleaners in all their grades of gasoline. so i think that possible advantage re additives/cleaners is no longer present.
i agree that there is zero benefit to using anything more than 87 octane in a car designed for 87.
the whole discussion is less important now that the percentage difference between low-octane gas and higher-octane gas is so much less than it was when gasoline was $1/gallon. there was a 20% difference back then between regular & premium. now there's a 6% difference.
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- #221 of 281
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Re: in cars designed for 91 max, does 92,93,94 help anything? [Mr_Shiftrigh [elias]
by Mr_Shiftright HOST
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May 09, 2006 (12:26 pm)
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Replying to: elias (May 09, 2006 12:23 pm)
that's a good point, never thought of that.
I guess what I was driving at is the common misconception that premium fuel is some kind of "doggie treat" for your car 
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