Quote:
Originally Posted by Muddedprairie
etc ... i have used 93 oct gas for over 2 years and i feel that has a good impact to the engin.... plugs are coming up soon...
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Believe what you want if it makes you feel good, but using the 93 octane fuel has impacted your wallet negatively while in no way positively impacting your 5.4.
Fact is, using higher octane fuel in these motors which are designed to operate on 87 octane fuel
can even negatively impact the engine in time with increased deposits.
There is no "extra power" in 93 octane fuel, there are no "extra cleaning agents" in it either. Higher octane simply refers to an increased resistance to preignition brought on by higher compression ratios or advanced timing or higher operating temperatures or super / turbo charging. The 93 octane lets you increase compression ratios, advance timing curves, or super charge or turbo charge the motor.
This increased octane is not more volitile, it's less volitile. It is harder to ignite, it's more resistant to ignition all else remaining equal. It performs well when increased compression pressures or advanced timing cause lower octane fuels to pre igniote uncontrolably before their plug fires or simply explode when it fires. Timing curves fire a plugbefore a piston reaches top dead center, while it's still compressing more, and a controled burn is what is needed. Not too fast, not too slow either as you don't need fuel burning after the piston is half way down the cylinder after TDC.
Higher octane is the result of additives that hinder or slow the ignition of the fuel. No extra power. It just lets you design a motor with higher compression, more timing, greater push on the piston when it tops over at TDC and goes down on the powerstroke.
When used in a lower compression motor, with factory timing, etc, the 93 octane at best, will make the same power as the 87 octane. There is a good chance that it may not perform as well, returning lower mileage even, due to it's formulated higher resistance to ignition which can slow it's full ignition when that plug fires, effectively acting like retarded ignition timing.
It can likewise, leave added deposits as it's full flame is later then in the combustion cycle, and thus cooler.
Not saying you'ld notice it so much in your 5.4, but I've had this same conversation with others using higher test gas in motors set up to operate on 87 octane, and have had more than one come back later and tell me they see an increase in mileage and even better response.
I have a '92 Thunderbird Sport 302 that I purchased with just over 130,000 actual miles, new trans and paint, well maintained car ... lady (
it was"her" car, not "his") and her husband who were original owners said they always had used 93 octane in it and told me to be sure to because it didn't run right on 87. I said I thought it said in the manual that 87 was correct, they told me no.
I didn't argue, just brought it home, looked in book, yep, 87 is fine. I tried a couple more tanks on 93, then switched to 87 octane after accumulating some real history of mileage records and getting a feel for the car. My mileage with 87 was a full half MPG better over same loop time after time, car feels pretty much same, never pings on 87. I live out in country, nearest town is 12 miles, we often go to one of two larger cities which are an hour each way, north or south. Loops are road miles, sometimes interstate, sometimes not.
It's an old wives tale that high test = better. Only when the engine is set up for the need of higher octane is it betterto use, and then it's usually necessary to use (
unless equipped with nock sensors to retard timing when 87 is used, like our '94-'06 LT-1 Caprice police cars were, they did run much better in lower two gears with 93, but it was because timing was advanced and nock sensors allowed them to, in high gear when engine gained rpms slower, when timing was on a slower curve, the 87 ran just as good).
