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850 Higher Octane = Worse MPG?? WTF???

volvoluvin

WWD for a while
Joined
Dec 17, 2003
Location
Poco Crib
Posted this on VS as well, but I'm seeing more and more 850 people on here...which I like, so I'll post here as well:

I've been playing around with my fill ups...Most of the time I run Chevron 92 octane, but for a dyno run a month back I went with Chevron 94, (Canuckistan goodness), and I noticed that my MPG was lower by 3-4mpg...bah I said, probably due to the dyno run and me putting my foot into it more often. But I couldn't remove the nagging feeling of how strange it seemed...so over the last month, I've gone between 92 and 94 twice...and it's conclusive...I'm getting worse gas mileage with 94...

Tank of 92 - 24mpg
Tank of 94 - 20mpg
Tank of 92 - 23.5mpg
Tank of 94 - 19.5mpg

I drive the same routes everyday, and I made sure to have the tranny set to sport for the whole test as well...

Anyone feel like weighing in on this?
 
Do you drive harder when you have the good stuff in there?

Like I said, that's what I thought about the very first time when I did the dyno run etc...

But for the test, I made sure to drive..."Like I always do"...this is a mix of punch it/slow/normal...so I would say no...
 
I have read that higher octane fuels contain less energy.

With the addition of ethanol, which has a LOT less energy, you will notice a significant dropoff.

You should run it for more than one tank and allow the ECU to experiment with the ignition timing. When it finds the sweet spot for premium fuels, you should notice an increase.
 
In my Bosch Automotive handbook. It lists premium fuel as having a slight amount more energy than regular fuel. In our area we have 10% ethanol in all the gas so it's a wash as to what the ethanol affect is.

Quote from my owners manual on page 71, 1993 240. "Volvo engines are designed for optimum performance on unleaded premium gasoline with an octane rating, AKI, of 91, or above. AKI, (anti knock index), is an average of Research Octane Number, RON and the Motor Octane Number, MON, (RON+MON/2) The minimum octane requirement is AKI 87 (RON 91).

In my 3rd edition Bosch Automotive Handbook. Specific calorific value. Table on page 232.
Regular gasoline has 42.7 MJ/kg
Premium gasoline has 43.5 MJ/kg

Not that much more but there is more power in premium gas. So go argue with the Bosch engineers if you want to keep believing there is more power in lower octane gas. ;-)

I don't know why the op car gets worse mileage but that should not be the case. It should be about the same since the octane is still within the optimal requirements. At least for my 240 this has proved to be the case. If I go lower octane than optimal I get worse mileage and worse performance.
 
In my Bosch Automotive handbook. It lists premium fuel as having a slight amount more energy than regular fuel. In our area we have 10% ethanol in all the gas so it's a wash as to what the ethanol affect is.

Quote from my owners manual on page 71, 1993 240. "Volvo engines are designed for optimum performance on unleaded premium gasoline with an octane rating, AKI, of 91, or above. AKI, (anti knock index), is an average of Research Octane Number, RON and the Motor Octane Number, MON, (RON+MON/2) The minimum octane requirement is AKI 87 (RON 91).

In my 3rd edition Bosch Automotive Handbook. Specific calorific value. Table on page 232.
Regular gasoline has 42.7 MJ/kg
Premium gasoline has 43.5 MJ/kg

Not that much more but there is more power in premium gas. So go argue with the Bosch engineers if you want to keep believing there is more power in lower octane gas. ;-)

I don't know why the op car gets worse mileage but that should not be the case. It should be about the same since the octane is still within the optimal requirements. At least for my 240 this has proved to be the case. If I go lower octane than optimal I get worse mileage and worse performance.

I never said it was fact, I said that is what I had read.

However, I have done many searches for information on the caloric content on different brands, octane, and blends of fuels, yet there is zero information out there.

I need to get this book you have.

Fuel stations should be forced to list the energy content in their fuels because I would certainly base my usage on the amount of energy I am paying for.
 
When I bought my 854t, all it had ever seen was 87 (poor car). I have put nothing less than 91 in, I usually put 94 in. At first I noticed a drop in fuel economy, but within the month, it was right back and surpassing where the 87 octane was in the L/100km. Give your car some time to adjust ignition timing.

How's the fuel filter/plugs doing?


Mike
 
The Btu and Octane content are important measurements. Found this link as it might help:
http://www.medfordfuel.com/octane.htm

The four most important properties of racing gasoline...
Listed below are the four basic qualities of fuels. As in everything there are trade-offs. You can't make a racing fuel that has the best of everything, but you can produce one that will give your engine the most power. This is why VP produces different fuel for different applications. The key to getting the best racing gasoline is not neccesarily buying the fuel with the highest octane but getting the one that is best suited to your engine. Octane is the rating of fuel's ability to resist detonation and/or preignition.

OCTANE is rated in Research Octane Numbers (RON), Motor Octane Numbers (MON), and Pump Octane Numbers (R+M/2). Pump Octane numbers are what you see on the yellow decal on the pumps at the gas stations and represents an average of the two. VP uses MON because this test method is more relevant to racing. Most other companies advertise RON because it is higher and easier to come by. Don't by fooled by high RON numbers or an average. MON's are the most important for a racing application. However, the ability of the fuel to resist preignition is more than just a function of octane.

BURNING SPEED is the speed at which a fuel releases its energy. In a high speed internal combustion engine there is very little time (real time - not crank rotation) for the fuel to release its energy. Peak cylinder pressure should occur around 20 degrees ATDC. If the fuel is still burning after this, it is not contributing to peak cylinder pressure, which is what the rear wheels see.

ENERGY VALUE is an expression of the potential energy in the fuel. The energy value is measured in BTU's per pound, not per gallon. This difference is important as the air fuel ratio is in weight not volume. Remember, this is potential energy value of the fuel, and this difference will show up at any compression ratio or engine speed.

COOLING EFFECT of the fuel is related to the heat of vaporization. The higher thhe heat of vaporization the better its effect on cooling the intake mixture. This is of some benefit in a 4-stroke engine, but can be a big gain in 2-stroke engines.
 
Phil, as mentioned above...

try 94 with at least 2-3 tanks without switching back. Let the ECU adjust and see if it improves.

If so, win. If not, oh well, stick with 92. Have it tuned to 92 to be on the safe side anyway.

FYI we don't have that ethanol blended **** here, unless you gas up at husky/mohawk

edit: on my HI-PO n/a setup I'd get better results using 89 octane.
 
The Btu and Octane content are important measurements. Found this link as it might help:
http://www.medfordfuel.com/octane.htm

The four most important properties of racing gasoline...
Listed below are the four basic qualities of fuels. As in everything there are trade-offs. You can't make a racing fuel that has the best of everything, but you can produce one that will give your engine the most power. This is why VP produces different fuel for different applications. The key to getting the best racing gasoline is not neccesarily buying the fuel with the highest octane but getting the one that is best suited to your engine. Octane is the rating of fuel's ability to resist detonation and/or preignition.

OCTANE is rated in Research Octane Numbers (RON), Motor Octane Numbers (MON), and Pump Octane Numbers (R+M/2). Pump Octane numbers are what you see on the yellow decal on the pumps at the gas stations and represents an average of the two. VP uses MON because this test method is more relevant to racing. Most other companies advertise RON because it is higher and easier to come by. Don't by fooled by high RON numbers or an average. MON's are the most important for a racing application. However, the ability of the fuel to resist preignition is more than just a function of octane.

BURNING SPEED is the speed at which a fuel releases its energy. In a high speed internal combustion engine there is very little time (real time - not crank rotation) for the fuel to release its energy. Peak cylinder pressure should occur around 20 degrees ATDC. If the fuel is still burning after this, it is not contributing to peak cylinder pressure, which is what the rear wheels see.

ENERGY VALUE is an expression of the potential energy in the fuel. The energy value is measured in BTU's per pound, not per gallon. This difference is important as the air fuel ratio is in weight not volume. Remember, this is potential energy value of the fuel, and this difference will show up at any compression ratio or engine speed.

COOLING EFFECT of the fuel is related to the heat of vaporization. The higher thhe heat of vaporization the better its effect on cooling the intake mixture. This is of some benefit in a 4-stroke engine, but can be a big gain in 2-stroke engines.

One thing that really suffered going from MTBE to Ethanol has been burn speed :(
 
the higher octane gas is more refined and contains more oxygen (hence higher octane) in the fuel which burns better, cleaner, and provides more energy per amount used. its simple science it would be impossible for the lower octane gas to perform better with hp or mpg's

id like to know the full effects of ethanol though
 
the higher octane gas is more refined and contains more oxygen (hence higher octane) in the fuel which burns better, cleaner, and provides more energy per amount used. its simple science it would be impossible for the lower octane gas to perform better with hp or mpg's

id like to know the full effects of ethanol though

Why does higher oxygen count towards higher octane (unless you are stating that because it is part of ethanol...the primary octane booster), a better burn (it doesn't), or more energy per amount used (its lower than old gas)? If the engine is not knock limited with 87 and the 87 has more BTU/gallon, it will most certainly get better mileage. Did you just make that stuff up?
 
As mentioned above. The B230F is optimized for higher octane than 87. So with 87 you are going to have knock instances especially under high load conditions. With retarded timing pulled by the knock sensor you are going to get worse mileage as well as less power. 87 is the minimum octane requirement. Not the optimal one.
 
Gasoline Gallon Equivalent (GGE) Table

Fuel Type
Unit of Measure
BTUs Per Unit
Gallon Equivalent

Gasoline, regular unleaded, (typical)
gallon
114,100
1.00 gallon

Gasoline, RFG, (10% MBTE)
gallon
112,000
1.02 gallons

Diesel, (typical)
gallon
129,800
0.88 gallons

Liquid natural gas (LNG), (typical)
gallon
75,000
1.52 gallons

Compressed natural gas (CNG), (typical)
cubic foot
900
126.67 cu. ft.

Liquefied petroleum gas (LPG or propane)
gallon
84,300
1.35 gallons

Methanol (M-100)
gallon
56,800
2.01 gallons

Methanol (M-85)
gallon
65,400
1.74 gallons

Ethanol (M-100)
gallon
76,100
1.50 gallons

Ethanol (E-85)
gallon
81,800
1.40 gallons

Bio Diesel (B-20)
gallon
129,500
0.88 gallons

Electricity
kilowatt hour
3,400
33.53 kwhrs



link:http://www.nafa.org/Template.cfm?Section=Energy_Equivalents
 
In my experience NA 240, 850 and 960 all get the same FE with 87 and 91 octane. I keep track of FE at every fill up. Anything more than 87 octane in NA volvo is a waste of money.

EDIT:
2002 s40 with 110k miles on the clock is averaging 30mpg over many fill ups on 87 octane. We use 91 octane on this car when air temp regularly gets over 90f
 
Last edited:
Higher Octane = Worse MPG

I was using 93 octane Shell gas in my 88 765 w/ B230FT. Over the winter I changed gas stations but still Shell, just not cut-rate Shell. Over the winter I used 93 octane and in the spring I changed to 93 mixed with 89 to get 91 octane. Now I am using 89 octane and have no problems with detonation. My MPG are also up 4 MPG since changing stations. My average MPG are now 22.4 MPG. I figure my MPG on how many miles in a month and how many gallons I used. I fill up on the first day of each month and I use the same gas pump every time time that I fill up. I keep records of odometer readings and $ amounts and gallons on every fill up.
 
the higher octane gas is more refined and contains more oxygen (hence higher octane) in the fuel which burns better, cleaner, and provides more energy per amount used. its simple science it would be impossible for the lower octane gas to perform better with hp or mpg's

id like to know the full effects of ethanol though

Just stop talking please, you're obviously either horrendously misinformed or just pulling things out of your ass.
 
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