Premium fuel w/ octane booster
Senior Member
Joined: Jul 2004
Posts: 6,200
Likes: 39
From: Easton, Pa.
Let me offer some basic thoughts on the effects of a change in octane in these Ford motors and not in reference to any other makes.
The Ford PCM and hardware combination uses cylinder rotation time as both a missfire monitor and a way to adjust running tables. (this is how the PCM adjusts for wear and conditions over time)
If octane fuel rating is changed such that combustion time is lengthened, the PCM has to detect this as a difference in rotation time and reflects accordingly in the software tables. This does not happen instantly but over a time span and driving cycles.
How much the ignition timing would change to match if much at all, higher octane, is anybodies guess.
The compression ratio and chamber characteristics all play a part in the OEM decision on what CR will be built into the motors and dictate the lowest octane for normal use. It's all an engineering package.
Since you have no control over ignition timing except via a tuner, using higher octanes can actually slow or reduce cylinder rotation/power production.
Why is an involved subject.
The use of so called octane improvers only effect octane improvements in one tenth octane increments not whole octane numbers. So are of little use unless in high concentrations in low amounts of gas, is in the tank.
Some octane booster have ingrediences that can coat the plugs and cause missfires under lean condition and EGR operations. The plugs have to rely on coil reserve voltage to fire plugs during lean running conditions and not have to deal with added causes of difficulty that takes all beyond limits. Add to this a coil that has a defect and reduces it's reserve voltage capability and you get missfire.
Fooling with octane boosters and hi octane fuel in stock engine is of very little value on a normal basis.
Some will profess to tell you they see a difference but I could ask what was the fuel being used before? Was it poor? Was the motor all carboned up before ? There are lots of reason one could see a difference that may not last. Just knowing what is being used can make a difference in the 'head' because you wanted it to.
I know I feel better driving a clean vehichle with no other changes.
The Ford PCM and hardware combination uses cylinder rotation time as both a missfire monitor and a way to adjust running tables. (this is how the PCM adjusts for wear and conditions over time)
If octane fuel rating is changed such that combustion time is lengthened, the PCM has to detect this as a difference in rotation time and reflects accordingly in the software tables. This does not happen instantly but over a time span and driving cycles.
How much the ignition timing would change to match if much at all, higher octane, is anybodies guess.
The compression ratio and chamber characteristics all play a part in the OEM decision on what CR will be built into the motors and dictate the lowest octane for normal use. It's all an engineering package.
Since you have no control over ignition timing except via a tuner, using higher octanes can actually slow or reduce cylinder rotation/power production.
Why is an involved subject.
The use of so called octane improvers only effect octane improvements in one tenth octane increments not whole octane numbers. So are of little use unless in high concentrations in low amounts of gas, is in the tank.
Some octane booster have ingrediences that can coat the plugs and cause missfires under lean condition and EGR operations. The plugs have to rely on coil reserve voltage to fire plugs during lean running conditions and not have to deal with added causes of difficulty that takes all beyond limits. Add to this a coil that has a defect and reduces it's reserve voltage capability and you get missfire.
Fooling with octane boosters and hi octane fuel in stock engine is of very little value on a normal basis.
Some will profess to tell you they see a difference but I could ask what was the fuel being used before? Was it poor? Was the motor all carboned up before ? There are lots of reason one could see a difference that may not last. Just knowing what is being used can make a difference in the 'head' because you wanted it to.
I know I feel better driving a clean vehichle with no other changes.