First time poster, long time listener..........

I have been considering switching from 87 octane to 93 octane

what should I expect in terms of increased fuel economy, and engine life?

thanks for any and all reply's

Craig

 

Welcome aboard, Craig

Basically you'll be wasting fuel in these engines. They were setup to run 87 octane unless you've modified the engine or its components in anyway.

Maybe someone can come along and explain exactly why.

 

Octane is a gasolines ability to resist knock. In a high compression engine a higher octane fuel is required.I think the v10 is 9.2:1 or something like that, not enough compression to require premium fuel. You wont notice any fuel economy or increased engine life, just less money in your wallet.

 

Big Orn is correct!!! don't waste your $$$ on a higher octane gas.

 

My F250 V10 was getting about 11.0mpg stock on 87

I installed a K&N filter system and it bumped up too 12.5 on 87

I installed a SuperChip and it bumped up to 13.2 on 87

I started to run 91 and it bumped up to 14.6

out of my two modifications what caused it to get better gas milage with 91octane.

maybe its a fluke, but I have put over 5500 miles on her now and still 14.6mpg

or maybe its a fluke? I will not rule that out I am a moron,

 

Don't worry, your not a moron...at least not determined by these posts!

The octance ratings are actually a rating percentage of the composition of the fuel...eg, its usually 87% octance (C8H18) and 13% heptane (C7H16). Some places use oxygen raided gas, to decrease the N2 outputs by adding extra O2, such as gas labeled 85.5 Octance. (If your bored and curious, Diesel is Dodecane - C12H26).

The gas mileage may increase slightly from higher octance when using a superchip or aftermarket computer. Though you cant physically adjust the compression ratio, you can adjust the fuel/air mixture, and higher octance combined with more air will give a better combustion to CO and CO2, instead of increasing the amount of fuel in the mix, affording less use of fuel at equal RPM's...make a note, that this is usually to trivial to notice, and using to high an octance rating in some vehicles can cause damage or produce terrible gas mileage.

PS my knowledge is book knowledge, not years of experience...for those with the experience, please feel free to retaliate

Whoo...asleep yet?

 

Higher octane can actually reduce mileage. Premium has a tendancy to not give a full burn, thus increasing emmisions and decreasing mileage.

 

Very impressed by all the answers!!! Been to many a board(including this one in the past) where people think by running higher octane and nothing else you'll magically make more power.If you're not pinging you don't need to upgrade.

The most ignorant ad I've seen lately is the STP ad touting "I've got jet fuel in my tank" Imagine running kerosene and see what happens.

 

Higher octane gas than necessary, to me, makes the engine feel sluggish at part-throttle, like it's colder than it should be... and higher octane gas does run colder. Hence, why you should have higher compression for higher octane gas - the higher the compression, the hotter the fire.

Also, because the fire is colder, it generates more carbon, which is a funny thing - the more high-octane gas you run, the more carbon buildup (higher compression), therefor, your engine is basically addicted to the higher octane... plus more CO (carbon monoxide) emissions because of the less-than-optimal burn.

The best thing is use a brand-name 87 octane that you know includes detergents (Amoco comes to mind)...

As to other vehicles' improved MPG with higher octane, it's possible those motors are preset to at least try to run at higher timing advance and use a knock-sensor to sense pinging. The higher octane you use, the more power because the computer will adjust. These Ford modulars are set to 87 octane. They hardly ever need anything more, and that's very rare, and if they start to ping, at least the V10 (that I know of) has a knock-sensor that will retard the timing even further.

As to V10SuperDuty1's question, the Superchips might already have pulled the timing advanced far enough that it wasn't running as well as it could be, as in just starting to ping. Also, the V10 has a knock-sensor, so if it did ping, the computer would retard the timing. Now, of course, putting in 91 gets rid of the ping, so the computer can advance the timing more, leading to more power...

 

Pinging is the fuel igniting slightly before the piston starts its downstroke. You get the best fuel burn, and thus power, just before a ping would occur. Modern computer controlled (factory) are configured to keep the burn just the good side of a ping. Higher compression requires higher octane and/or less ignition advance to not ping. Higher octane basically burns slower so the explosion of the fuel is slightly slower.

So as stated above, unless you have modified your engine with more compression or added a performance chip (which re-maps the ignition and fuel ratio curves) you get less performance from going with a higher octane fuel than what the factory recommends.

If your engine is pinging at higher altitudes or temperatures then running higher octane temporaily will save your pistons/rings from melting. But if pinging is happening all the time during normal driving then you should get it checked out, something might be confusing the computer, like a bad sensor somewhere.

 

Higher Octane fuel actually has less energy per gallon than lower octane fuel. Like others have said, perfomance loss will result in an engine not designed to run premium.

I have a superchips tuner and it makes a big enough increase in mileage with premium to offset the extra cost.

Eric

 

The higher the octane the slower and colder the burn of fuel. The timing has to be set correctly on the computer controlled ignitions to take any advantage of higher octane. Thus, that is what chips and tuners do. They advance the timing to accomodate for higher octane fuel. Factory set-ups need 87 and 87 only.

 

Actually, pinging is the fuel burning prior to the sparkplug igniting it. And way prior to the piston beginning it's downward stroke, in fact the piston is still traveling upwards when the spark fires (which has the benefit of cushioning somewhat the violent stopping of the piston traveling up which can actually stretch rod bolts and rods). Most engines at high rpm are set to have the plugs fire at 30-36 degrees before top dead center. You are correct in stating that higher octane burns slower, so ignition has to be advanced not retarded to ensure complete burn. Octane prevents pre-ignition, or ping so ignitions can be advanced and still achieve a complete burn of available fuel, peace, Ken

 

Any engine that has an OBDII computer advances the timing to the point of pinging several times per second. If it can't make the engine ping, it think's something is wrong and will pull a whole bunch of advance out and make the engine run like crap. The way to fix it is to go back to the lower octane fuel and it will clear itself usually in one tank.
And actually "pinging" can be either pre-ignition (so-called spark knock) from a variety of causes or the premature explosion of the end gases of a more or less normal combustion event (also called detonation).