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  #13  
Old 01-23-2011, 03:18 PM
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Re: Gasoline

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Originally Posted by NetJunkie View Post
Better mileage? Says who. I get better on 87 than I do on 89 in my 5.7 GC. Doesn't have anything to do with compression? Yeah, it does. Higher compression means lower octane gas will ignite sooner which is why you get detonation if your octane is too low on a high compression engine. A lower compression engine doesn't care. If you aren't getting detonation running 87 under heavy load when the engine is hot then there is no need to go 89 or higher. Same reason I used to run 104 octane in my Z06 Vette when we'd do dyno days in July. Running 93 I'd see the PCM pull timing at high RPMs because of detonation due to heat (and high compression).

Waste the money if you want to and if it makes you feel better, do it. But to say either the V6 or V8 will run "better" on 93 is not correct unless, again, the computer is pulling timing due to detonation.

No one is saying there will be damage or a significant downside to using 93 or higher...but in almost all cases you won't get a benefit either.

We are talking about gasoline octane not about particular engine specs; in general higher octane is better and no way harmful to any gasoline engine. It was time long ago when I ran my car on mix of 86 and diesel 50/50 and it runs too but doesn’t mean I would suggest this
Again to my point - if they said it is Ok to use 87 that doesn’t mean to me it was design strictly and only for 87. It is marketing step for US only since 90% of people prefer 87 as cheap alternative. In Europe they have different standard and octanes. Simply just use 93 and see if you will be getting any mpg advantage or not, I believe I will.

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Old 01-23-2011, 03:23 PM
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Re: Gasoline

I have tested 89 and 87 for MPG on the same exact highway trips that I do frequently. I get 1 more MPG on 87 than 89 on the same 150 mile round trip. I really doubt 93 is going to give me 10%+ more MPG than 87, which is what it would take to even out the cost.
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  #15  
Old 01-23-2011, 03:29 PM
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Re: Gasoline

If you've read How Car Engines Work, you know that almost all cars use four-stroke gasoline engines. One of the strokes is the compression stroke, where the engine compresses a cylinder-full of air and gas into a much smaller volume before igniting it with a spark plug. The amount of compression is called the compression ratio of the engine. A typical engine might have a compression ratio of 8-to-1.

The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.

The compression ratio of your engine determines the octane rating of the gas you must use in the car. One way to increase the horsepower of an engine of a given displacement is to increase its compression ratio. So a "high-performance engine" has a higher compression ratio and requires higher-octane fuel. The advantage of a high compression ratio is that it gives your engine a higher horsepower rating for a given engine weight -- that is what makes the engine "high performance." The disadvantage is that the gasoline for your engine costs more.

putting 87 octane in a hemi will decrease fuel milage as the fuel is igniting before what the engine is designed for. the ignition is supposed to puch the piston back down the cylinder and rotation the crack (from what i understand) if this ignition happens too soon you are wasting energy for those two strokes as the other two strokes are for exhaust. not to mention the damage to the piston (over time) as the ignition is trying to force the piston back down before the stroke has completed
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Old 01-23-2011, 09:12 PM
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Re: Gasoline

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Originally Posted by NetJunkie View Post
I have tested 89 and 87 for MPG on the same exact highway trips that I do frequently. I get 1 more MPG on 87 than 89 on the same 150 mile round trip. I really doubt 93 is going to give me 10%+ more MPG than 87, which is what it would take to even out the cost.
Agreed. As long as one doesn't experience detonation where the ECM pulls timing back, 87 has a higher BTU (energy) content than 93 and will yield better fuel economy. I'm sticking to 89 in my Hemi because it is only a few cents more per gallon...for peace of mind.
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  #17  
Old 01-23-2011, 11:56 PM
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Re: Gasoline

One of the best responses I ever heard to this debate came from an OEM engineer, who said that using higher octane fuel in an engine designed for lower octane is like wearing size 12 shoes when you are a size 10.
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Old 01-24-2011, 06:38 AM
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Re: Gasoline

  • Quote:
    Originally Posted by Geronimo View Post
    engine designed for lower octane

I doubt design like this exist, adjustments to accept 87 yes. Words from my book: "Accepting 87".
Wrong analogy as well, 93 is like wearing light and more advanced sneakers instead of heavy and loud boots (87) ... Both will walk with no harm!
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Old 01-24-2011, 07:47 AM
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Re: Gasoline

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Originally Posted by Breitling65 View Post
I doubt design like this exist, adjustments to accept 87 yes. Words from my book: "Accepting 87".
Wrong analogy as well, 93 is like wearing light and more advanced sneakers instead of heavy and loud boots (87) ... Both will walk with no harm!
Sorry, I can't stay out of this any longer considering your statement is patently wrong. While using the higher octane fuel will do no harm there are many reasons why you should not use it if the vehicle you are driving does not call for it.

1. Cost, you are simply throwing away money. If the engine is configured to run optimally with a lower octane fuel the higher octane WILL NOT allow the engine to perform better.

2. Reduced fuel economy, while usually not enough to me measurable, can occur due to the higher octane vs. heptane levels in 93 octane fuel. At it's basic level, not getting into the specific chemistry, the number you see on the pump is the ratio of Octane vs. Heptane. 87 means 87% Octane, 13% Heptane. Octane is a longer chain molecule and releases less energy when ignited than Heptane. 93 Octane gas actually generates slightly less energy when it burns thus reducing the HP output of your motor causing you to use more fuel to obtain the same performance. This may seem counter intuitive since "high performance" engines require higher octane fuels. It's not when you consider the higher compression ratios and resultant power output greatly outweighs the slight reduction in energy in the high octane fuels.

3. Reduction in performance (see item 2).

Using 93 octane fuel in an engine designed to run on 87 or 89 octane IS like putting a size 12 shoe on a size 10 foot!
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Old 01-24-2011, 08:40 AM
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Re: Gasoline

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Originally Posted by Breitling65 View Post
I doubt design like this exist, adjustments to accept 87 yes. Words from my book: "Accepting 87".
Wrong analogy as well, 93 is like wearing light and more advanced sneakers instead of heavy and loud boots (87) ... Both will walk with no harm!
Ohh well I tried
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Old 01-24-2011, 08:53 AM
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Re: Gasoline

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Originally Posted by Breitling65 View Post

I doubt design like this exist, adjustments to accept 87 yes. Words from my book: "Accepting 87".
Wrong analogy as well, 93 is like wearing light and more advanced sneakers instead of heavy and loud boots (87) ... Both will walk with no harm!
Stop listening to the marketing for BP and Exxon. They want you to buy 93 even if you don't need it. They make more money on it. Others have given you all the reasoning there is. Engines don't "tune down" to 87. If they don't need 93 they don't need 93.
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Old 01-24-2011, 09:34 AM
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Re: Gasoline

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Originally Posted by NetJunkie View Post
I have tested 89 and 87 for MPG on the same exact highway trips that I do frequently. I get 1 more MPG on 87 than 89 on the same 150 mile round trip. I really doubt 93 is going to give me 10%+ more MPG than 87, which is what it would take to even out the cost.
Around here, the often use ethanol in a 10% mixture to achieve the 89 octane rating. This will cause lower gas mileage. 89 is clearly tagged as contain as containing up to 10% ethenal when 87 is not. (not saying 87 doesn't have ethanol it, just not tagged) There are many gas stations that sell 89 at the same price as 87
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Old 01-24-2011, 09:35 AM
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Re: Gasoline

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Originally Posted by NetJunkie View Post
Stop listening to the marketing for BP and Exxon. They want you to buy 93 even if you don't need it. They make more money on it. Others have given you all the reasoning there is. Engines don't "tune down" to 87. If they don't need 93 they don't need 93.
If they sense detonation they do in essence tune down (pull timing)

Just sayin
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Old 01-24-2011, 09:46 AM
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Re: Gasoline

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Originally Posted by mrpositraction View Post
Around here, the often use ethanol in a 10% mixture to achieve the 89 octane rating. This will cause lower gas mileage. 89 is clearly tagged as contain as containing up to 10% ethenal when 87 is not. (not saying 87 doesn't have ethanol it, just not tagged) There are many gas stations that sell 89 at the same price as 87
For the past decade atleast, here in the Chicago area every grade of gasoline at every gas station all say contains 10% ethanol. The good thing is atleast in my cars fuel economy has been above average so im not going to complain and say I have been getting poor fuel economy and its all due to ethanol.
My current 2000 Lexus ES300 according to the sticker says 19/25. I average 24 around town and 31 highway. My 2006 Z06 Corvette says like 18/25 I average 20 around town and 30 highway. I cant complain too much about ethanol I guess :-) Soooo if gasoline did not contain ethanol would I potentially be getting 34mpg highway in my 505hp Z06? haha I dunno
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