Other Talk "Otterville" plus Religion/Politics

Let's talk about octane

Old 07-03-06, 03:11 PM
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Let's talk about octane

The owner's manual for my car says to use gas with an octane rating of at least 87. Do I get any benefit whatsoever from using a higher octane? I'm happy to pay the extra $2 per fill-up for the 93 if it means I'll have better performance/mileage/engine life/whatever, but I don't want to spend the money if there's no benefit.
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Old 07-03-06, 03:18 PM
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Originally Posted by JasonF
The owner's manual for my car says to use gas with an octane rating of at least 87. Do I get any benefit whatsoever from using a higher octane? I'm happy to pay the extra $2 per fill-up for the 93 if it means I'll have better performance/mileage/engine life/whatever, but I don't want to spend the money if there's no benefit.
No, higher octane only means it is harder to ignite, specifically auto-ignition from the compression stroke. Higher compression engines need higher octan to avoid knocking. If you don't need it (engine isn't knocking), don't pay for it.

Some claim the "premium" (higher octane) gasolines also contain more detergents, help clean your engine, etc. That is highly debatable at best.
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Old 07-03-06, 03:19 PM
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Thanks, OldDude.
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Old 07-03-06, 03:24 PM
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No arguements with what old dude said - solid advice

but Paging matta to the octane thread
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Old 07-03-06, 03:39 PM
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More expensive = better for your car!
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Old 07-03-06, 03:47 PM
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Ford salesman recommended me not to go higher than 87, it will cause some sensor act up.
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Old 07-03-06, 03:57 PM
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Originally Posted by OldDude
No, higher octane only means it is harder to ignite, specifically auto-ignition from the compression stroke. Higher compression engines need higher octan to avoid knocking. If you don't need it (engine isn't knocking), don't pay for it.

Some claim the "premium" (higher octane) gasolines also contain more detergents, help clean your engine, etc. That is highly debatable at best.

'Zackly!
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Old 07-04-06, 01:28 AM
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Originally Posted by 4KRG
No arguements with what old dude said - solid advice

but Paging matta to the octane thread
old jokes will never die. never. die.
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Old 07-04-06, 02:59 AM
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I finally found out what OldDude was saying recently. It pains me to think how much I could have saved over the past 10 years or so buying the lower octane.
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Old 07-05-06, 10:00 AM
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My problem is my car should be using 91, and never lower than 89. I buy 93 sometimes, sometimes 89. Sunoco has 91 but they are few and far between around here.
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Old 07-05-06, 11:23 AM
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I don't buy it when manufacturers say "your care needs at least X Octane". Does it run noticeably different with the lower octane? If not, then use it.
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Old 07-05-06, 11:24 AM
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Octane threads are a modern day "Mattsignal".
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Old 07-05-06, 06:43 PM
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Originally Posted by LurkerDan
I don't buy it when manufacturers say "your care needs at least X Octane". Does it run noticeably different with the lower octane? If not, then use it.
you should run the octane the manuf. recommends. most modern engines have knock sensors that will pull the timing, but if your car is designed for 91, and you use 87, then you're gonna get a lot more timing pull, which leads to a shorter engine life.

back to the OP's question, you might have some marginal gains running higher octane due to less timing retard, but this depends on how the system was designed. with a higher octane, you can advance your timing, but this is only recommended if you know what you're doing, and it may void portions of your warranty.
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Old 07-05-06, 06:44 PM
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Originally Posted by OldDude
No, higher octane only means it is harder to ignite, specifically auto-ignition from the compression stroke. Higher compression engines need higher octan to avoid knocking. If you don't need it (engine isn't knocking), don't pay for it.
my next car will have a 10.3:1 CR /w a turbo. gotta use 91 for it
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Old 07-05-06, 07:42 PM
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Originally Posted by 4KRG
No arguements with what old dude said - solid advice

but Paging matta to the octane thread
I thought this as well.
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Old 07-05-06, 07:45 PM
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What's a matta?
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Old 07-05-06, 08:26 PM
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we lost matta, thats whats a matta
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Old 07-05-06, 11:03 PM
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Originally Posted by The Bus
My problem is my car should be using 91, and never lower than 89. I buy 93 sometimes, sometimes 89. Sunoco has 91 but they are few and far between around here.
Can't you just fill your tank with half 89, half 93?
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Old 07-06-06, 12:01 AM
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Originally Posted by Shazam
Can't you just fill your tank with half 89, half 93?

i don't think octane is linear.
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Old 07-06-06, 12:08 AM
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Originally Posted by D.Pham00
i don't think octane is linear.
I'm certainly no expert, but somebody thinks it is...

For a gasoline to function properly in an engine, it should not begin to burn before it is ignited by the spark plug. If it does, it makes the noise we think of as engine "knock." The octane-number scale rates the anti-knock characteristics of a gasoline. This linear scale is based on heptane, given an octane number of 0, and on 2,2,4-trimethylpentane (an octane constitutional isomer), given an octane number of 100. The higher the octane number, the better the anti-knock characteristics. If you had a barrel of heptane and a barrel of 2,2,4-trimethylpentane, how would you blend these compounds to come up with a 90 octane mixture?

Solution
Since, by definition, heptane is zero octane and 2,2,4-trimethylpentane is 100 octane, a mixture of 10% heptane and 90% 2,2,4-trimethylpentane would produce a 90 octane mixture.

http://college.hmco.com/chemistry/ge...tions/ch24.pdf
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Old 07-06-06, 06:47 AM
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Originally Posted by D.Pham00
i don't think octane is linear.
Maybe not exactly to half a dozen decimal places, but it is pretty linear. This is the basis of Sunoco's selector pumps which get several (7-8??) blends out of two ground tanks.
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Old 07-06-06, 06:34 PM
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Originally Posted by OldDude
Maybe not exactly to half a dozen decimal places, but it is pretty linear. This is the basis of Sunoco's selector pumps which get several (7-8??) blends out of two ground tanks.
huh. good to know. i didn't think it was, but then again, i never really bothered to look it up. now, if only there was a place where you can buy high octane unleaded (the highest that's easily acquirable around here is 100/101)
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Old 08-01-06, 09:53 PM
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Originally Posted by 4KRG
we lost matta, thats whats a matta
Nah, I still lurk every once and awhile. Just really busy these days.

And I'm leaving this octane thing alone -- getting RandyC to believe me is the whole reason I'm going back for my Ph.D. Why can't I ever please you daddy? :matta:
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Old 08-02-06, 12:46 PM
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20/20 says no.

http://abcnews.go.com/2020/story?id=2188905&page=2

Ways to Save

This is not to say there's nothing you can do to save on gas. Some NASCAR fans told us they use upper-grade gas because they say it gives them a little bit better mileage, more power and a cleaner engine.

But that's a myth, one of many debunked in "20/20's" new book, "Myths, Lies and Downright Stupidity."

Lots of people are fooled. Just this week, cops arrested eight men for allegedly passing off regular gas as premium at New York gas stations. They were caught only because investigators wiretapped the suspects the customers never noticed enough to complain.

Some older cars need higher octane. And cars with high-compression, high-revving engines need higher octane gas to run smoothly. But most don't.

Check your owner's manual 90 percent of today's new cars have low-compression engines. They don't need high-octane gas, and you're wasting your money if you buy it.
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Old 08-02-06, 12:59 PM
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Originally Posted by The Bus
My problem is my car should be using 91, and never lower than 89. I buy 93 sometimes, sometimes 89. Sunoco has 91 but they are few and far between around here.
Where do you get 93?
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