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Old 06-26-2006, 11:55 AM   #29
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Fuel saving myths abound...but somewhere in the back of my collective consiousness I recall that premium (ie. higher octane) fuels burn longer than their regular counterparts.
This longer burn results in more BTU's and more complete combustion. The end result could be a modest fuel economy boost but the more important factor is reduced emission of unburned fuel.
I'm just glad Airstream One lives on regular fuel. The cost of premium would have me in the poor house.
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Old 06-26-2006, 12:26 PM   #30
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In general I usually go with the vehicle manufacturers recommended fuel.....BUT....I also may downgrade if the engine does not knock or ping under load with a lower grade gasoline.

If you go to the auto forums you will get 180 degree answers from the pros. So who knows for sure, I think it is a matter of individual circumstances including engine type, terrain, driving style, etc.
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Old 06-26-2006, 01:30 PM   #31
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Using todays prices, if using non-ethanol (premium) gas resulted in a 12% increase in milage the price per mile is a wash, a 20% improvement (which is often claimed) would save $1.94 per 100 miles, or about 2 cents per mile improvement. Doesnt sound like much at first glance, however, given a 4,000 mile trip this is just over $75. Even a 15% (likely as I read) increase in milage would give you about a penny an mile boost. So I guess the smart money is on watching the split between regular and premium gas.
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Old 06-26-2006, 01:53 PM   #32
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Lots of information here, but it seems to be scattered in such a way as to be confusing.

"Compression ratio" is the ratio of the compressed gasses at top dead center of the piston travel expressed as the ratio between the compressed gasses and normal atmospheric pressure. Theoretically, it is possible to get more performance out of an engine with higher compression, which is why most Porsche, Audi, Mercedes, BMW, Corvette, and other high performance cars specify higher octane fuel. At higher altitudes (Denver), normal air density is lower to start with and so the compression ends up lower as well, allowing the use of lower octane than would be necessary at sea level - but also producing lower power.

Octane is a rating system which describes a fuelís propensity to ignite under pressure. The higher the number, the higher the compression ratio can be before spontaneous ignition. The BTU content of 87 octane is the same as 92 octane, but as noted above, it is possible to get more power out of the higher octane gas by compressing it more before ignition. On the other hand, unless you have an engine with enough compression to take advantage of it, higher octane will do no good at all.

As noted in other posts, fuel with 10% ethanol will have a lower btu than straight gasoline, so premium gasoline without ethanol will likely produce better milage than ethanol/gasoline blends, not because of the octane, but simply because more btu's are available.

The compression ratio of an engine does not necessarily stay constant over time. In the old days engines routinely accumulated enough combustion by-products in the cylinder head to significantly increase the compression ratio. So it was common for 50's and 60's cars to need premium gas after 60,000 miles or so, unless the heads were "decarbonized". With the cleaner burning fuels of today this happens much more slowly, if at all.

"Pinging", or "knock" is the spontaneous ignition of the fuel/air mixture prior to the firing of the spark plug. This means that the affected piston is forced to further compress expanding gases. Since the piston cannot actually move backwards against the other cylinders in the engine the pressure forces inside that cylinder become many times higher than the design parameters. A blown head gasket, broken wrist pin, broken piston, cracked head, cracked cylinder liner, broken block, deformed rod bearings, or broken rod are all possible. Severe knock will wreck an engine in minutes, but the light, occasional "pinging" most of us are familiar with will merely reduce the engine life from, say, 300,000 miles to only 175,000 miles.

A hot engine will knock more readily than a cooler one. This is why it sometimes occurs while towing, but not in ordinary driving.

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Old 06-26-2006, 02:35 PM   #33
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Quote:
Originally Posted by j54mark
Lots of information here, but it seems to be scattered in such a way as to be confusing.
Mark
To recap. The question was if there was an advantage to using premium gas.

As I follow the main points....

The issues are two:
1) Higher octane does not help, unless your vehicle is designed for it, in which case you need to be using it anyway.
2) One important difference between the fuel grades is that non-premium gas often has 10% ethanol which does reduce performance. The sub issue is how much performance you loose and how wide the gap in prices between regular and premium is in order to justify the added price for improved performance.

Does this sum up things to this point?
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Old 06-26-2006, 02:41 PM   #34
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Boy what a complicated mess. It was news to me that Premium might not contain Ethanol. Time to start looking more closely at the lables on the pump. I know some say something about "may" contain up to 10% ethanol and others say something like "oxygenated gasoline" (bubbly )

I knew it was a mess with different States and different regions in parts of States requiring certain blends depending on time of year. I didn't know about some of the problems associated with Ethanol besides lack of performance and the unintended environmental damage done by some of the other laws. Interesting read:

http://www.sfgate.com/cgi-bin/articl...AG04H9IQG1.DTL

It's so hard to separate the politics from the science:

8/15/2003 Gov. Gray Davis is renewing his push to eliminate ethanol as a federally mandated clean-air additive to California gasoline. But the embattled governor's prospects of persuading the Bush administration to reverse itself - a move that would disappoint the president's Midwestern supporters who have their eyes on a new market for their corn product - may be no better than of surviving the Oct. 7 recall election.


Could it be we're replacing "Big Oil" with "Big Corn"


I still haven't been able to find out if the drop in milage compensates for the "cleaner" emissions. In Washington it's all based on % of gas in the exhaust but if you're burning more fuel per mile then the total volume (and mass) of you're exhaust is greater.


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Old 06-26-2006, 03:21 PM   #35
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Quote:
Originally Posted by j54mark
Octane is a rating system which describes a fuelís propensity to ignite under pressure. The higher the number, the higher the compression ratio can be before spontaneous ignition. The BTU content of 87 octane is the same as 92 octane, but as noted above, it is possible to get more power out of the higher octane gas by compressing it more before ignition. On the other hand, unless you have an engine with enough compression to take advantage of it, higher octane will do no good at all.
but the aftermarket chip reprogrammers claim to boost performance...some, only with the use of premium. another one claims "some" gains w/ regular, but more w/ premium. what's up w/ that?
Quote:
Originally Posted by j54mark
As noted in other posts, fuel with 10% ethanol will have a lower btu than straight gasoline, so premium gasoline without ethanol will likely produce better milage than ethanol/gasoline blends, not because of the octane, but simply because more btu's are available.
I've been watching since they made the 10% ethanol change here. On my first tank in the truck, I recorded among the highest mpg I've ever clocked. Haven't had the chance to re-check, because I don't have the truck most of the time (the mrs. uses it as her daily-driver...I take the car on the 32 mile commute to save gas). The car does not seem to have been negatively impacted, either, coming in at 26mpg last check. no particular effort to drive conservatively on my part, either. In the past, I've clocked a maximum of 27, but only when really trying (i.e. keeping it below 65mph).
Quote:
Originally Posted by j54mark
The compression ratio of an engine does not necessarily stay constant over time. In the old days engines routinely accumulated enough combustion by-products in the cylinder head to significantly increase the compression ratio. So it was common for 50's and 60's cars to need premium gas after 60,000 miles or so, unless the heads were "decarbonized". With the cleaner burning fuels of today this happens much more slowly, if at all.
well...the last Taurus I had started pinging at 60-70k miles. "mid-grade" would stop it. The present Taurus is also starting to ping slightly under acceleration (80k). I really don't want to upgrade the gas at these prices, though. wish there were something else I could do....
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Old 06-26-2006, 04:28 PM   #36
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Be aware that a 'new' ethanol blend often is only replacing an old MTBE ether oxygenator cocktail, when I lived in Washington DC area they changed to oxygenator blends to reduce summer smog and our vehicles would promptly loose 8-12% milage on the switch over... So what was being sold before ethanol that gave such lousy milage? No matter what, ethanol won't provide same energy as petroleum and has to use more for same output...

I am tempted to add 2 or 3% diesel to each tank just to try compensating for the ethanol here in Minnesota. Back east the no-name gas station with best price always has product that smells like diesel, comes from a tank farm in the Port of Baltimore and maybe a by-product of cleaning tankers or piplelines but gives good mileage when I am there.

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Old 06-26-2006, 05:03 PM   #37
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but the aftermarket chip reprogrammers claim to boost performance...some, only with the use of premium. another one claims "some" gains w/ regular, but more w/ premium. what's up w/ that?
It would seem that some of the chip makers boost performance by the time-honored method of advancing the timing. And it can work. Ford sales would drop like a stone if all of a sudden you had to use premium in their family cars, so they calibrate them to run smoothly on regular.

There are a lot of factors involved. Car sized automatic transmissions and radiators can only handle so much heat, so some engines are deliberately de-tuned accordingly. Yes, your Chevy Duramax CAN make 500 hp.; but your radiator can't cool it - there is a reason why the grilles in medium duty trucks are so large.

There are pollution issues as well, which is why people frequently (but not always) must replace their hot rod chip with the factory one to pass an emissions test.

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Old 06-26-2006, 05:10 PM   #38
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Some of the replacement chips only trick the throttle position sensor into believing it is open wider than it really is. Result: the fuel injectors shoot more fuel into the cylinder, voila.....more horsepower. Downside...gas mileage takes a hit. I'm saying "SOME" not "all". You can save the price of the chip by pushing your gas pedal down farther! Some miracle cures aren't!
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Old 06-26-2006, 06:27 PM   #39
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Diesel in with your gas to improve performance? I've never heard that trick before. If it works I'd still be very leary of what it would do to platinum plugs, catalytic converters, fuel injectors, etc. Don't diesels all run fairly extensive fuel filtering systems? I know someone that got diesel in his MG gas tank once and it was an expesive repair. I don't think it'll mix completely with the gas but rather sink to the bottom risking an expensive repair.

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Old 06-27-2006, 12:07 AM   #40
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Diesel is a NO-NO with gas motors!!!

Also heard of EXTENSIVE and EXPENSIVE repairs associated with diesel into a gas motor. ANY. Period.

There are MORE THAN ENOUGH other additives you can buy/ add or otherwise aquire that will boost octane, and prevent knock.

Of course, if you add up the 'per tank' cost of the additives, higher octane gas still is cheaper.... Just using MY calculator though..... Your math may vary.

Use the proper (manufacturor indicated) octene gas and all will be well, you will likely get the indicated mileage (or close depending on your right foot), and you will get loads of miles out of the vehicle....

The vehicles built these days are WAY better than those built years ago.

That is NOT to say that the oldies aren't goodies, but then they have learned a thing or a zillion in the interem....

Get the gas rated for your TV and you'll be "a happy camper".....

What more can we ask for???

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