Which Octane Fuel should you use? Putting higher octane fuel is not always better. | Page 2 | GTAMotorcycle.com

Which Octane Fuel should you use? Putting higher octane fuel is not always better.

miggs said:
My car is custom tuned and needs to run on 91 due to spark and timing adjustments.
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Is there a 94 map available for your car? I can tell the difference with mine, especially in the hot summer months where the ECU will pull timing on 91 with the higher IAT's.
 
GreyGhost said:
Extra range with regular or premium? What car/engine? Technically regular has more energy in it than premium. If you are getting better range from premium your ECU is playing around with fueling and/or timing. Interesting to see you get that big of a difference.
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2014 Ford Focus, 5 spd manual, 2 litre 4 cylinder, and yes, get around 550 km/tank on regular, 650 on high test
city driving makes no difference which fuel I use, the increased range with premium is highway only
 
DJM said:
Is there a 94 map available for your car? I can tell the difference with mine, especially in the hot summer months where the ECU will pull timing on 91 with the higher IAT's.
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There is the ability to retune for 94, ...or 106 if you want to track only on leaded race fuel
 
Anyone compared how clean 87 vs higher octane burns...carbon buildup inside engine?

I put 87 and my car idles rough, 89+ and smooth idle.
It's not the car...engine is smooth like butter with 89+.

Also doesn't ethanol corrode the fuel system over time?

What did we do before ethanol additives?
 
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I think there are some engines that can sense what octae level fuel you are burning and adjust things like timing to take advantage of the different fuels. This may also explain why some cars do better mileage on different octanes.
 
taximan62 said:
I think there are some engines that can sense what octae level fuel you are burning and adjust things like timing to take advantage of the different fuels. This may also explain why some cars do better mileage on different octanes.
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Almost all cars have a knock sensor (or similar). They advance timings/lean out engine as per their program until they start detecting knock and/or misfire. If the car was designed for low test, I wouldn't expect much difference running premium. If it was designed to run premium and was fed low test it would retard timing and/or dump in extra fuel to keep things from blowing up. The focus above getting 10% extra mileage on premium still makes little sense to me (unless the driving behaviour changes or maybe Ford have let the car go outside of the normal fuel/timing map if the other sensors are happy).

I believe that E85 detection is done with an actual sensor in the fuel, but it is very rare that you will find a vehicle with that.
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