Contour Enthusiasts Group Archives Forums Modifications Duratec Performance Octane and Mileage

And given that higher octane indicates higher knock resistance i.e. the gas is harder to burn, he was probably choking his engine with carbon the whole time. Not good.

It never ceases to amaze me how people won't follow their owner's manual. Like they are smarter than the teams of engineers that spend years developing these systems...oil level in the Duratec being the obvious exception

Octane has nothing to do with fuel economy...directly.

Pulling timing is not done at cruising speeds; rather it is done at light load to full throttle loads and is based on knock. When the throttle is reduced back to light cruise loads the timing should be the same or comparable.

Therefore, octane in this case has nothing to do with your fuel economy.

I am not saying that running a higher octane fuel in a car engineered for regular octane will give you better fuel milage. Fuel economy is determined by a number of variables, including the energy content of the fuel and the condition of your vehicle, neither one of which have anything to do with the octane level of the fuel. Two fuels of identical octane could have different energy content due to a difference in composition and therefore can give you different results.
I do know that for whatever reason in a couple of cars I have owned, in particular a 93 probe gt (which required reg fuel) 'seemed' to run better on the higher octane.
In the z, I adjust the timing with a switch (MSD) when a higher octane isn't available (it is built to run on 94). Retarded timing equals less power, and less available power equals more pedal....

Also the lower the octane number, the more explosive power it has. High-octane fuels burn slower, so a cooler burn. Cooler burning fuels mean less pinging and fewer emissions.

Using high-octane fuel in a vehicle that doesn't need it is just a waste of money....that's the bottom line.

the burn rate of the fuel doesn't mean it has more power or in your terms energy. Higher octane fuels use different structured molecules like branched chain hydrocarbons versus a higher percentage of straight chain hydrocarbons.
Benzene ring has 6 carbons, so pentane. Relatively speaking and definitely in low efficiency car engines, the small difference in structural changes affects available energy very little.
I doubt it affects the fuel economy at all!

Running high octane in a car designed for 87 is pointless. It is good to run 89 in a car designed for 87, but anything over that is pointless because the computer is set for 87. My dad runs 89 octane on his fleet of about 130 trucks (mostly F150s) because its proven to be better. They have a lot less problems running 89 then when they ran 87

Yeah the bottom line is to use what is recommended. I have a friend that wastes money using 93 in his motorcycle that only needs 87. (and we have tested it). Just follow the guidelines........it does suck that we have to use 93 when the gas prices are so darn high!

Is there a reason nobody has mentioned compression ratio in this discussion? You run a certain octane based on your compression ratio, not based on timing. Ocatane is the ability of the fuel to resist combustion under compression. If you run cheap fuel in a high compression engine the fuel will ignite before the ignition lights it strictly from being compressed. That is detonation. You can cause detonation by advancing your timing because it ignites the fuel before the optimal time in the engine's stroke.

9.8:1 is the cuttoff for running 91 octane pump gas at sea level. Higher compression than that you need to start thinkin about race fuel. I am not sure what these contours have, I don't have one, YET, but I doubt they require 91 octane unless you are right at sea level. The higher in elevation you are the less air going into your engine wich lowers compression in the cylinder, so you can use cheaper fuel.

If you run high octane where you don't have the compression to get it to ignite, you are wasting fuel and potential energy in the wasted fuel every time the cylinder fires. Resulting in lost power and fuel mileage.

If your car gets better mileage on the cheap stuff, and the "seat-of-your-pants" feel is better, run it, that means it works better. Higher elevation and lower humidity will allow you to run cheaper fuel.