What fuel are you running 87 89 91
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RaiderSilverGT
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- Oct 11, 2004
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Performance on $2.45 SoCal 87 octane is flawless. Why would I pay even more?
BTW: 18.5 MPG overall. Hard to resist merging with authority...otherwise would be better.
BTW: 18.5 MPG overall. Hard to resist merging with authority...otherwise would be better.
Rootus
Officially Addicted
The lower octane fuels make more horsepower. The only time to switch to higher octane is when you start advancing the timing -- you might get a few more ponies from advancing the timing than you lose from the higher octane.
That is very true. The higher octane fuel takes longer to burn, so therefore when the timing is advanced, maximum benefit of the fuel can be acheived. I have personally seen a drag car on a chassis dyno that made 12 more rwhp running 87 octane versus 93 octane. Anyone who is not putting 87 in their car is wasting money. The engineering on today's engines are far supreme of what they were even 5 years ago. Gone are the days of higher octane is better, so now are the days of getting the maximum amount of hp out of THE FUEL our engines were designed to use. 
REDFIRE 05 GT
New Member
Octane= resistance to burn.
So the higher the octane the more resistance to burn. The sole reason for higher octane is to prevent pre-ignition (ping). Mostly cars with superchargers, turbos, or high compression need the higher octane levels. This is because they have higher pressure in the cylindars as compared to lower compression vehicles or non-boost vehicles. There is always more heat generated by increased pressure. In a high compression or boosted application this high heat can actually ignite the fuel air mixture in the cylindar before the spark plug ignites the mixture. At this point the cylindar is firing out of time (way before tdc) which means the piston getting pounded down down while it is trying to go up. This is called ping. This is what will put holes in pistons.
So what they did was create a gas that can actually take more heat before it will ignite (or raised the flashpoint). This way the spark plug can do the job of igniting the mixture.
On a side note a top fuel dragster would have a hard time starting on the nitro mixture because the octane is so high. To help them start one up you see the mechanics spraying 87 octane right in the butterflys on the scoop out of a spray bottle. This way it will light up easy.
I think the key is to look at your owners manual and see what Ford recommends. NOBODY KNOWS MORE THAN THE PEOPLE THAT ACTUALLY DESIGNED THE ENGINE IN YOUR CAR.
So the higher the octane the more resistance to burn. The sole reason for higher octane is to prevent pre-ignition (ping). Mostly cars with superchargers, turbos, or high compression need the higher octane levels. This is because they have higher pressure in the cylindars as compared to lower compression vehicles or non-boost vehicles. There is always more heat generated by increased pressure. In a high compression or boosted application this high heat can actually ignite the fuel air mixture in the cylindar before the spark plug ignites the mixture. At this point the cylindar is firing out of time (way before tdc) which means the piston getting pounded down down while it is trying to go up. This is called ping. This is what will put holes in pistons.
So what they did was create a gas that can actually take more heat before it will ignite (or raised the flashpoint). This way the spark plug can do the job of igniting the mixture.
On a side note a top fuel dragster would have a hard time starting on the nitro mixture because the octane is so high. To help them start one up you see the mechanics spraying 87 octane right in the butterflys on the scoop out of a spray bottle. This way it will light up easy.
I think the key is to look at your owners manual and see what Ford recommends. NOBODY KNOWS MORE THAN THE PEOPLE THAT ACTUALLY DESIGNED THE ENGINE IN YOUR CAR.
Mr_dcj2001
Member
87 is the way to go. Besides, here in great Cali 91 octane is over $2.50 a gallon 
(depending where you are). RaiderGT, I feel your pain. 
(depending where you are). RaiderGT, I feel your pain. I have heard, however, that the lowest fuel grade often doesn't have the cleaning agents that the plus and super fuels have, is this true?
I have two Fords, a 2000 GT vert, and a 2004 Expedition. I have heard both of them knock slightly under hard loads (acceleration or trailer pulling) so I use 89, this has solved the issue permanently.
I have two Fords, a 2000 GT vert, and a 2004 Expedition. I have heard both of them knock slightly under hard loads (acceleration or trailer pulling) so I use 89, this has solved the issue permanently.
GusinCA said:
As you car ages it can increase compression ratios so that the next grade may need to be used. Really all cars are different and all engine wear is different. If you car starts out with 87, but over time it builds up carbon which increases compression and the 89 may be needed, but as it ages it will wear parts and lower compression which in the end may end up back at 87.
Remember also the Octane Rating is based on the Research and Motor Methods. R +/- M. It is an average of both. There is usally an 8 point gap between them. To get 87 octane, they will take a research method and come up 91 Octane while the motor method will show 83 octane. Just add 4 points for the Research Rating and minus 4 for the motor method.
As for cleaning agents i find that to be a load of crap. Gasoline distilled from crude oil has a very low octane rating. Its octane rating can be increase by adding chemical agents. Back when lead was used it was a cheap and easy way to increase octane yet keep price down. Now they use a whole bunch of chemicals such as tertiary butyl alcohol. I don't see anyone adding lead into their engines today. So to say 87 is dirty over 93 doesn't make sense since they come from the same source yet one has more added octane increasers over the other.
I also don't see how gasoline, which is very corrosive could be a cleaning agent inside the engine. It doesn't have anytime to dissolve anything within the engine. I don't know many solevents that work instantly and most need to soke for a while.
If you put your car under a heavy load, such as towing, you may need to increase the octane just to protect it. A engine under towing conditions is usally an engine working at or near its peak. Drag racing works an engine at or near its peak. If you go to the track its sometime worthwhile to increase octane to protect your engine at the sametime possibly lowering performance. Some engines work better due to higher octane, but a jump from 87 to 93 won't help at all. While an 87 to 89 could without a cut in perfomance. Also note that many cars have high and low octane table to account for the different fuels. My GTO can run fine on 87 octane with a higher chance of preignition even though it recommends 91 octane. The car is able to switch between the table to get the best run from then engine. Its not instantaneous as the car learns and responds to whats going on, but in the end i will lose performance because its a lower octane then the optimal settings recommends.
Only use higher octane when needed or required, otherwise your possibly lowering performance and wasting money. In my case i don't have 91 octane in my area and i can only get 87,89,93 so i get 93 because my car recommends 91.
SN95_XB331
New Member
If I recall, I thought the 05 has knock sensors in it (finally!). So that with the better electronics will compensate and still optimize performance (and could lower performance from a perspective). Any cleansers, etc.. is not desired--they may clean the carbon as advertised, but usually clog the injectors in the end. Best to run basic gasoline (no detergents) and then use a gas treatment (one time detergents) at major service intervals.
Conclusion: 87 (as the directions say)
Conclusion: 87 (as the directions say)
This comes from how stuff works website
"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 4.6L has a 9.8:1 compression ratio and is borderline (IMHO) as far as needing to go to a higher octane rating. My understanding is: knock senors eliminate early detonation as a problem but it costs you some hp - as the engine studders a little bit.
"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 4.6L has a 9.8:1 compression ratio and is borderline (IMHO) as far as needing to go to a higher octane rating. My understanding is: knock senors eliminate early detonation as a problem but it costs you some hp - as the engine studders a little bit.
Glenns05 said:
Doesn't the 05 also have Variable Valve timing, which will help it get the most out of the gas you put in it? The 2004 had a 9.4:1 ratio. With the new 3-valve and variable valve timing the newer engine is able to get the most out of what you put in it to a point. If you add more safe guards (higher octane) it cannot get more out of it, only what its originally capable of. And in some cases worse results due to the nature of chemical reactions.
All About Variable Valve Timing
Either way i got all of the information out of science books and various readings on Gasoline and Octane ratings. Do what you want. Even if you put 93 octane in your car in the end it will only cost you about $100- $200 more a year in gas.
Just an FYI...Just because you buy gas at an Amaco station, it doesn't mean the gasoline was refined in an Amaco refinery. All refiners blend gasoline to a spec and it all gets dumped into the same pipeline where it goes to the distributor. The gas you buy at Amaco could come from a Chevron or ExxonMobil refinery. The only difference between brands are the additives (i.e. Chevron Techron). Base gasoline is the same no matter where you buy with the exception of little mom and pop stations that will buy off-spec gas and sell it slightly lower than the name-brand stations.
Before anyone questions me on this, let me say that I work in one of the largest refineries in the US and have worked with the CEs responsible for gasoline production. I've also worked closely with our lab people who are responsible for assuring the gas meets spec.
BTW, where I work is also the only facility in North America that produces Mobil 1 so I know a little about that as well.
Rootus
Officially Addicted
Sounds like people might be confusing variable valve timing with variable spark timing. Engines have been using variable spark timing for a very long time. It has no relationship at all to the valve timing.Glenns05 said:
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