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I know we have the better MPG thread, its mostly tune up and driving tips. So with our high fuel prices and now we have what are considered low MPG vehicles, lets see some advice about which gas octane rating we are using for best performance and why.

For me I use 89, my BKO has a high lift cam with short duration, advanced timing, hot spark system, 5spd. I also live in eastern PA with mile long mountains.
using 87 I get about 16mpg and the engine runs poor. 89 gets me 18mpg and the engine idles beautiful, exhaust has a crisp thunderous sound, and acc. is great and smooth. now 93 is just a waste I get 14mpg good idle and crap for performance.
 

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I Paid for this sh!t
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i dont need any octane, i use NO.2 Diesel Fuel. Preferably OFF Road, but Onroad is ok too, i Use additive to boost my cetane and lubricity...
End hijack

But in my bronco when it was still 351, it was 87 octane all the way
14* timing, headers, straight pipe no muffler, smog delete, egr delete, and custom tune, netted me 23mpg at 80-85mph over 800 miles, on average i ran about 18/19
 

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most people report no difference with MPG's. you're finding a way to justify your added expense. 85 mountain blend, or 87 if I'm flatlanding it. Runs perfect and does about as good as it can on gas. anything more is a waste unless you have a high performance motor built to run on higher octane.
 

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Your Compression Ratio dictates the Octane Rating. The Octane Rating tells you how much the fuel can be compressed before it spontaneously ignites, otherwise known as Detonation.

A high performance engine with a 11:1 high compression ratio requires slower burning compression resistant fuel of higher octane. A stock engine with a 8:1 lower compression ratio can efficiently use a faster burning less compression resistant lower octane fuel which saves money.

In other words, 87 Octane gasoline is gasoline that contains 87-percent octane and 13-percent heptane (or some other combination of fuels has the same performance of the 87/13 combination of octane/heptane). It spontaneously ignites at a given compression level, and can only be used in engines that do not exceed that compression ratio.

Knocking or pinging generally requires adjustment of the ignition timing and/or the use of a higher octane fuel. The ignition timing due to the speed of which the gasoline burns and the octane rating due to it's compression resiliency.

As a side note, some time ago refineries found that they could add tetraethyl lead (TEL) to cheaper grades of gasoline to enhance it's octane rating. Hence, "ethyl" or "leaded" gas. After lead gasoline was generally banned due to environmental hazards, refineries were forced to use higher grades of gasoline at more expense. 100 octane leaded Aviation AvGas is still available for aircraft.

Stock compression for a 302 is 9:1. Stock compression for a 351W is even less at 8.8:1.

BTW, a non-working or removed EGR can also cause Detonation as well. A working EGR reinserts small amounts of exhaust into the intake manifold that, although hot, still has a cooling effect on combustion temperatures by diluting the air/fuel mixture slightly. When the cooling effect is lost, it creates higher combustion temperatures under load and an increased chance of detonation. Believe it or not.
 

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What about the elevation factor? When I had my 95 Vette I could run 87 octane in Colorado(where I lived at the time)at about 6000 ft without any problems, when I took trips to CA and put 87 in it it would knock and ping like a mother.
I wouldn't think elevation would have any effect on BKO engines, as far as different octane levels go anyway.
 

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What about the elevation factor? When I had my 95 Vette I could run 87 octane in Colorado(where I lived at the time)at about 6000 ft without any problems, when I took trips to CA and put 87 in it it would knock and ping like a mother.
I wouldn't think elevation would have any effect on BKO engines, as far as different octane levels go anyway.
Really no affect on my bronco 5.8. I've never touched the timing, 85 up here, 87 down at sea level. Only because 85 is the lesser blend here and 87 is usually the lesser at sea level. never knocks.
 

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What about the elevation factor? When I had my 95 Vette I could run 87 octane in Colorado(where I lived at the time)at about 6000 ft without any problems, when I took trips to CA and put 87 in it it would knock and ping like a mother.
I wouldn't think elevation would have any effect on BKO engines, as far as different octane levels go anyway.
Good question!

Your Air/Fuel Ratio was changed by the elevation causing you to run lean. Rich fuel mixtures resist detonation while lean ones do not. Although EFI uses oxygen and barometric pressure sensors to compensate for changes in air density, a vehicle calibrated for high altitude driving will typically run lean if driven at a lower elevation.

Hence the EPA required "High Altitude Principle Use" option on the Ford Bronco. This was required PCM programming for Broncos sold in EPA designated high altitude counties and fringe areas to prevent pollution and lean conditions when changing elevation.


 

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Good question!

Your Air/Fuel Ratio was changed by the elevation causing you to run rich. Rich fuel mixtures resist detonation while lean ones do not. Although EFI uses oxygen and barometric pressure sensors to compensate for changes in air density, a vehicle calibrated for high altitude driving will typically run rich if driven at a lower elevation.

Hence the EPA required "High Altitude Principle Use" option on the Ford Bronco. This was required PCM programming for Broncos sold in EPA designated counties and fringe areas to prevent pollution when changing elevation.


believe that went away with the newer broncos. disconnect battery, let computer "relearn" once at location and there should be no problem with lean/rich. Not that I actually do that to avoid detonation.
 

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Your Air/Fuel Ratio was changed by the elevation causing you to run lean. Rich fuel mixtures resist detonation while lean ones do not. Although EFI uses oxygen and barometric pressure sensors to compensate for changes in air density, a vehicle calibrated for high altitude driving will typically run lean if driven at a lower elevation.

Hence the EPA required "High Altitude Principle Use" option on the Ford Bronco. This was required PCM programming for Broncos sold in EPA designated high altitude counties and fringe areas to prevent pollution and lean conditions when changing elevation.
I changed my post as I meant to say lean, not rich. :doh0715:
 

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just run the lowest octane you can without knocking. if you have no knock with 87, putting 93 in it is just wasting money.
 

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Your octane requirements are dictated by cylinder pressure, which is determined by your static compression ratio, timing, and camshaft duration. Running a higher octane than is required to keep your engine from detonating is a waste of money. If it doesn't ping on 87 then run 87. Even with 14* of base timing and a stock cam it is hard to get a 5.8 to ping with stock heads because the static compression ratio is so low.
 

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you guys and you fancy 87 octane, i run that good stuff, 85 octane haha
 

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the elevation change is due to the oxygen content of the air... when you go up in elevation the oxygen level decreases requiring less fuel... when you add oxygen fuel burns faster requiring a richer mixture... its rather quite simple really... if youve ever messed around with the jetting of carburetors be it on race cars, bikes, or four wheelers which i have on all... hehehe
 

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yo
Tips to Avoid Lean Conditions TSB 91-8-13; "...Rough idle, hesitation, poor throttle response, induction backfire and stalls during cold start/warm up may be caused by the poor volatility of some high octane premium grade unleaded fuels (91 octane or higher (R+M)/2). When compared to regular grade unleaded fuel (87 octane (R+M)/2), high octane premium grade unleaded fuel may cause long crank time.
ACTION: Use a regular grade unleaded fuel in all vehicles, except where a premium unleaded fuel is recommended in the Owner Guide. If lean air-fuel type symptoms are experienced, determine the grade and brand of fuel used and offer the following service tips. Advise those using a higher octane grade fuel to switch to a regular grade unleaded fuel. For those using a regular grade fuel, advise them to try another brand. Do not advise using a higher octane unleaded fuel than is recommended for that specific engine. Ford engines are designed to perform best using a high quality regular grade unleaded fuel. Only advise using a higher octane unleaded fuel to avoid potentially damaging spark knock or ping, but do so only after mechanical fixes are ineffective. NOTE: ALL UNLEADED GASOLINES USED SHOULD CONTAIN DETERGENT ADDITIVES THAT ARE ADVERTISED AS HAVING "KEEP CLEAN" OR "CLEAN UP" PERFORMANCE FOR BOTH INTAKEVALVES AND FUEL INJECTORS..."
Source: by Ford


Octane Recommendations in a 96. Your vehicle is designed to use regular unleaded fuel with an octane rating of 87. In most cases, it is not necessary to use a fuel with an octane rating higher than 87. At service stations, the octane rating is displayed on a label on the pumps. In some parts of the country, “regular” grade fuels are sold with octane ratings of 86 or even less, especially in high altitude areas. We recommend that you do not use these fuels. Always use a fuel with an octane rating of 87, even if it is sold as a “midgrade” or “premium.” Do not be concerned if your vehicle sometimes knocks lightly when you drive up a hill or when you accelerate. However, if a fuel with the recommended octane rating knocks heavily under all driving conditions or knocks lightly driving at cruising speed on level roads, see your dealer or a qualified service technician. Persistent, heavy knocking can damage the engine..." read more
Source: by Ford via Hiller Ford via miesk5 at FSB

Fuel Volatility TSB 98-26-2 for 87-96
Some vehicles using winter blend fuels may exhibit a stall on start up and a no restart, hard start condition or a no start condition in unseasonably hot weather (greater than 27°C/80°F). These concerns may be related to fuel volatility from winter blend fuels during winter-spring and autumn-winter transitions and may result in a fuel pump vapor lock condition. This condition may appear to be a fuel pump failure but may be caused by winter blend fuel.
ACTION Refer to the following text for further information.
NOTE: FUEL TANK ADDITIVES WILL NOT RESOLVE THESE CONCERNS BECAUSE VAPOR FORMS FROM CAVITATION WITHIN THE FUEL PUMP. FILLING THE TANK TO FULL MAY BE EFFECTIVE. ADVISE CUSTOMER TO USE THE RECOMMENDED OCTANE GRADE PER OWNER MANUAL AND NOT A HIGHER GRADE.

Explain to the customer that this concern may be due to a low tank level of winter blend fuel combined with unseasonably warm weather. Advise customer that filling the fuel tank to full may be effective in resolving this concern. Also, advise customer to use the recommended octane grade per their Owner Manual and not a higher grade.

Background
Gasolines are seasonally adjusted, meaning they have higher volatility (vaporize easier) in the winter and lower volatility in the summer. Government mandates to improve air quality have resulted in significant changes to gasolines, such as the mandatory use of oxygenates (ethanol, methyl tertiary butyl ether (MTBE), and others) in the winter or the reduction of Reid Vapor Pressure (RVP) in the summer. The addition of oxygenates (especially ethanol) increases volatility while the reduction of RVP reduces volatility.

Gasoline distribution practices often do not allow branded marketers to have much control over their gasoline's volatility other than RVP. Oxygenate (e.g., ethanol, MTBE) use is more dependent on local gasoline markets, rather than specific marketers practice. Therefore, it is difficult to recommend specific brands to avoid volatility related complaints.
Source: by Ford via miesk5
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Fuel Economy Service Tips TSB 90-6-15 in 4.9L, 5.0L & 5.8L for 85-90 Bronco, E &, F Series
Source: by Ford via Chilton
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Fuel Economy Tech Tips TSB 99-26-09 for 90-96 Bronco, 90-97 F Series, Aerostar, F 350; 90-92 Ranger & Econoline; 91-2000 Explorer; 95-2000 Windstar; 97-2000 Expedition & Many Others

Fuel Stabilizer TSB 92-11-10 for 88-92 Bronco, Aerostar, Explorer, F Series & Ranger
Source: by Ford
Publication Date: MAY 20, 1992
LIGHT TRUCK: 1988-90 BRONCO II
1988-92 AEROSTAR, BRONCO, ECONOLINE, F SUPER DUTY, F-150-350 SERIES, F-47, F-53, RANGER
1991-92 EXPLORER
ISSUE: During extended periods of vehicle storage (60 days or more), gasoline may deteriorate due to oxidation. This may damage rubber components and other polymers in the fuel system. It may also eventually clog small orifices in the fuel charging system.

ACTION: Add Ford Gas Stabilizer (E8AZ-19C544-A) or an equivalent commercially available fuel stabilizer such as "STA-BIL" to the vehicle's fuel tank whenever the actual or expected storage periods exceed 60 days. The instructions packaged with the product should be closely followed. The vehicle should be operated at an idle speed to circulate the additive throughout the fuel system.
PART NUMBER/ NAME
E8AZ-19C544-A Gas Stabilizer
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TSB 99-26-09 Fuel Economy Techtips
IF THE IMAGE IS TOO SMALL, click it.

ISSUE: Customers may perceive that vehicle fuel economy is lower than it should be, based upon Environmental Protection Agency (EPA) estimates. Fuel economy is most influenced by vehicle usage and duty cycle.

ACTION: Refer to the Figures of this TSB. Consult this TSB and share with customers to improve their understanding of fuel economy factors.

MPG TechTips - Economy/Mileage Improvement

See also:

TSB 96-10-07 California ReFormulated Gasoline (CaRFG)

ISSUE: California introduced CaRFG around March 1, 1996 and statewide it must be available at all service stations by June 1, 1996 to help reduce emissions and improve gasoline quality. It will replace the traditional gasoline sold in Northern California and improve the reformulated gasoline that has been sold in Southern California since January 1995. California Air Resources Board (CARB) projects smog forming emissions from motor vehicles to be reduced by about 15 percent.

ACTION: The following text is provided to give some answers to some commonly asked questions by our customers.

POSITION: Ford Motor Company recommends the use of CaRFG as a cost effective means of reducing emissions to provide cleaner air. We have participated in vehicle and laboratory testing of CaRFG to make sure it is acceptable for our customers' use. There are no unusual vehicle performance concerns expected based upon these studies. The use of CaRFG will not affect Ford's new vehicle and/or emissions warranty.

WHAT DOES CaRFG CONSIST OF?
CaFRG consists of the same basic components as other gasolines, but it reduces pollution because of its cleaner burning components. Features are:
> reduced aromatic hydrocarbons to form less smog emissions
> added oxygenates to reduce emissions
> decreases the amount of fuel evaporating from the vehicle
> lowered sulfur content to provide more efficient operation of the vehicle's catalytic converter
> reduced benzene by about one-half

IS CaRFG MORE HAZARDOUS THAN CONVENTIONAL GASOLINES?
CaRFG is a hazardous substance like convential gasoline. Precautions should continue to be taken to avoid exposure to vapors or liquid when it is pumped or handled. It should never be siphoned or swallowed.

HOW WILL CaRFG AFFECT VEHICLE PERFORMANCE?
Properly blended CaRFG should have no adverse effect on vehicle performance or the durability of engine and fuel system components. Its basic properties are not significantly different than other cleaner burning gasolines that have been used in the U.S. for several years.

If the vehicle is a certified California calibration 1996 or later model year, it was designed to operate on CaRFG gasoline. The vehicle will operate satisfactorily on gasolines in the other 49 states, but emission control system performance may be affected. Using gasolines other than CaRFG have substantially increased emissions from motor vehicles.

WILL THE USE OF CaRFG AFFECT CALIFORNIA VEHICLE WARRANTY?
No. The coverage of Ford's new vehicle warranty is not affected. In fact, Ford Owner Guides have consistently approved the use of properly blended reformulated gasolines containing oxygenates. Further information about properly fueling your vehicle is included in the Owner Guide.

WILL FUEL ECONOMY BE AFFECTED?
A very small reduction in fuel economy of less than one-half mile per gallon is possible if the customer was using gasoline without oxygenates. This is attributed to the lower energy content of oxygenates which have been in all Southern California gasolines since January of 1995 and in some gasolines since the 1970's.

Many factors affect fuel economy like driving habits, vehicle maintenance, weather conditions, etc. Fuel economy can vary by more than a mile per gallon from one fill-up to the next with the same gasolines. For further details see TSB Article �95-12-2� for customer expectations regarding fuel economy.

ARE SPECIAL ADDITIVES NECESSARY FOR CaRFG?
No. It is not necessary to add anything to the vehicle fuel tank after the gasoline is purchased from the service station. California regulations require deposit control additives in CaRFG to minimize port fuel injector and intake valve deposits.

WILL OLDER VEHICLES OPERATE SATISFACTORILY WITH THE NEW CaRFG?
Older vehicles are expected to operate satisfactorily on CaRFG because vehicles have been operating on gasolines similar to CaRFG for a number of years. However, considerable testing indicates that older, high mileage vehicles are more susceptible to fuel system problems due to age and normal wear and tear regardless of whether they are operated on conventional or CaRFG gasolines. Owners of these older vehicles are encouraged to follow their vehicle manufacturer's recommendations regarding vehicle maintenance.

WILL THE SMELL BE DIFFERENT THAN CONVENTIONAL GASOLINE?
CaRFG is not expected to smell different than the gasoline most vehicles are currently using. If an unusual odor is noticed, it would probably be from oxygenates. Most service stations use vapor recovery systems to minimize the release of gasoline vapors while refueling. The use of CaRFG should result in little or no "rotten egg" smell from the exhaust because CaRFG has much lower sulfur than conventional gasoline.

WAS CaRFG TESTED BEFORE INTRODUCTION?
It was tested for over five million miles in more than 800 vehicles under the guidance of CARB including experts representing automobile manufacturers, gasoline suppliers, fleet operations and government. There was no increase in problems identified with the use of CaRFG.

DOES CaRFG COST MORE?
The price at the pump cannot be accurately predicted, although a modest increase is likely. The price of CaRFG is subject to the competitive forces in the marketplace. Many factors including production costs, supply and demand, weather, crude oil prices, and taxes affect gasoline prices.

WHERE CAN I GET MORE INFORMATION ON CaRFG?
Additional information within the state of California on CaRFG is available from the California Air Resources Board toll-free at 1-800-922-7349 (within California only).
 

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I've always heard, if your engine dont need the higher octane, it's wasted. But having said that, I got to admit that my truck runs better on avgas. (100LL) I've not noticed any differnce between 87, 89 and 91. I run 89 just to be safe. One thing I will mention is I do notice a differnce in mpg running ethinal free gas.
 

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I run 89 now cause its the same price as 87 at some stations here in missouri and because it appears to make my 300 run better

BTW, a non-working or removed EGR can also cause Detonation as well. A working EGR reinserts small amounts of exhaust into the intake manifold that, although hot, still has a cooling effect on combustion temperatures by diluting the air/fuel mixture slightly. When the cooling effect is lost, it creates higher combustion temperatures under load and an increased chance of detonation. Believe it or not.
Maybe thats why my f150 started to go downhill and run like shit right before i traded it for my bronco... SUCKS to be that guy in Illinois who got it cause he's gotta pass emissions!:goodfinge

my brother thinks he knows everything "you don't need that emissions shit on here, its just putting exhaust back into the motor" but apparently it matters lol
 

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All very good points being made!
 
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