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Guest Message by DevFuse

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Don't waste your money with Premium gas!


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45 replies to this topic

#41 OFFLINE   fbov

fbov

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Posted 21 October 2013 - 03:35 PM

First off, Gary, I had a '73 Celica, and your reports of varying mileage with different gas brands would explain a recent trip we took... and it adds another control/noise factor!

 

The one other point is to remember we have Atkinson cycle engines, 12.3:1 compression assumes a 2L intake. at 1.8L, it's more like 11:1 compression, but with a 10% longer power stroke. Conversely, a hybrid engine runs at higher avg. load, so one would expect an adaptive engine to eventually use the added octane productively. It's something to test...

 

HAve fun,

Frank









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#42 OFFLINE   Tree63

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Posted 26 October 2013 - 12:13 PM

In my part of Canada, ethanol is added to Regular (up to 10% in 87 octane) but not to Premium (91).  I don't know if the octane level is maintained with the ethanol added, or if  it is 87 before adding the ethanol and it slips a bit.

 

With my last car (2007 Nissan Sentra), I tried Premium for 6 months and basically saw a 10% FE improvement with a 12-14% price premium.

 

Based on reading earlier postings on the Forum, I decided to try Premium for July-Dec, and am basically seeing the same results (a little behind with Fuelly entries).  (My 600+ tank reported in Forumm was on Regular.)  I'm up to 33000km/20000 miles so well past any break-in considerations.

 

Another factor:  Had the PCM update done about a week ago so too early to add that into the picture, but seemed a bit better on highway trip to the cottage, even with colder weather (mid 30's F) - 5.8 vs 6.2 l/100km at about 110km/hr.

 

Regardless the ride in C-Max is great.

 

ps - tried a tank of "super premium" (octane 94) from a national brand and FE dropped!!  Maybe ECU reprogramming couldn't handle it.


Edited by Tree63, 26 October 2013 - 12:15 PM.


#43 OFFLINE   ptjones

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Posted 26 October 2013 - 02:48 PM

IMO from the Testing I've done Premium does improve MPG's around one or so, but not worth the money.(20-30 cents/gal). Pure gas(90 octane) improves about 2MPG still not worth it.(70-80 cents/gal.)

Paul



#44 OFFLINE   Tdefny

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Posted 26 October 2013 - 04:31 PM

I don't buy into the whole idea of higher octane gas paying off in MPG. Octane rating measures the ability of a fuel to resist detonation (early ignition). Ethanol increases octane rating but decreases mileage, as it is less volatile than gasoline.

A higher compression engine needs the detonation resistance but can get better performance from the higher compression. It needs to detune itself slightly or risk damage if a lower grade of fuel is used. Our Atkinson-Miller cycle engine is more of a high expansion engine. It doesn't use the high compression to get more fuel into a tighter space like a performance engine. Rather, it uses a normal charge and retains it slightly longer to get a little more thermal efficiency.

The energy from fuel comes from breaking carbon bonds and turning them into CO2. Ethanol has fewer carbon bonds and thus less energy. I believe that Ethanol is all they have used to raise octane rating since MTBE was banned, but I am not sure of that.

#45 OFFLINE   ptjones

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Posted 26 October 2013 - 05:03 PM

I don't buy into the whole idea of higher octane gas paying off in MPG. Octane rating measures the ability of a fuel to resist detonation (early ignition). Ethanol increases octane rating but decreases mileage, as it is less volatile than gasoline.

A higher compression engine needs the detonation resistance but can get better performance from the higher compression. It needs to detune itself slightly or risk damage if a lower grade of fuel is used. Our Atkinson-Miller cycle engine is more of a high expansion engine. It doesn't use the high compression to get more fuel into a tighter space like a performance engine. Rather, it uses a normal charge and retains it slightly longer to get a little more thermal efficiency.

The energy from fuel comes from breaking carbon bonds and turning them into CO2. Ethanol has fewer carbon bonds and thus less energy. I believe that Ethanol is all they have used to raise octane rating since MTBE was banned, but I am not sure of that.

They use lead in AVGAS and EPA continues to threaten to ban it,but with no viable replacement  they can't.(it's not a big problem % of volume is small) I'm only using my experience, but for what ever reason all FORD cars That I have owned have gotten better MPG's with Premium over Regular. And it's still not worth the additional cost unless you have need to go farther. Pure gas is the best, but very expensive here.

Paul



#46 OFFLINE   marshtex2

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Posted 28 October 2013 - 12:46 AM

I spent 30 years in fuel research at big ol' Texaco, Product Research, and we looked long and hard into everything about the various grades of fuel.

 

The higher grades of gaso had more aromatics than Regular making them more dense, more mass per unit volume.  The carburetor cars showed better mpg with the higher grades because the carburetor system sucked the gaso over a hump to get it into the metering port.  About the same mass of the more dense fuel was sucked over and that meant less volume.  Hence fewer gallons to go the mile, throttle position staying constant.  That led to all kinds of myths about better mpg with Premium gaso and was great as a selling point for the more profitable product to buyers who didn't need the increased octane rating.  Back with leaded gaso, the lead increased the fuel density, and more lead was in the premium gaso to get the higher octane rating, hence contributing to the better mpg impression.  The volatility of the fuel influenced startablilty and drivability at lower temperatures.  The more volatile components are less dense and would tend to take away from an mpg rating.

 

With the expanded use of fuel injection, which meters the fuel by volume in a sealed system, fuel volatility was less to no influence and the direct effect on mpg went away.  However, the same volume of the more dense fuel means more mass of fuel into each combustion event, hence more power.  A driver looking for fuel economy and pussy footing the throttle pedal can get the desired performance/power with slightly less throttle thereby bringing a little better mpg. 

 

A second however is that most drivers' rampage on the throttle overrides these effects and any improved mpg won't be seen.  It takes very carefully controlled conditions to document these differences.

 

This consideration carries on to ethanol or any oxygenate.  They are less dense than the gasoline hydrocarbon and additionally bring in less energy for their combustion event.  Thus they are detrimental to fuel economy on a per gallon basis at equivalent power settings.

 

Marshall


Edited by marshtex2, 28 October 2013 - 12:57 AM.

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