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So today I was talking to a few people and they asked what fuel I use in my car. I told them 89 ( Midgrade ) and something was being said that vehicles that are turboed/turbo'd? Should run the highest such as 93. I know the Manual says 87 so what is everyones opinion? What do you think or know is best and have noticed from the different octanes? I am needed a learning of this!
 

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You are more prone to knock with the cheaper gas. Thats no Bueno, the higher you go the less knock you will experience.

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The stock tune can accommodate 87 octane. You'll be safer with higher octane and get a bit more power

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A stock Focus ST can run from 87 to 93 octane. It automatically adjusts for fuel within this range. With the higher octane fuel, ignition timing can be advanced more before knock occurs. This advancement in timing produces a little more power.

So basically, you don't have to run 93, but you'll make a bit more power if you do.
 

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Dyno runs done on a ST by CJ Ponyparts with graphs..Google it utube..
Showed the engine has a major (like 15hp) decrease in power over 5,500 rpm on 87 (vs 93)
The engine management reduces timing on 87 OVER 5,500rpm.
SO...IMO this means if you really never runs the engine up over 5,000rpm 87 is JUST AS GOOD
(in reality the 87 gas does have a few less hp than 93 below 5,500.. but it is so small a difference below 5,500 rpm..
You cannot really notice it.)
 

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I notice slightly better gas mileage on 91 than on 87 but I did the math and it does not offset the extra price they charge for premium (93 is not that common around here, 91 is usually our premium) so you still end up paying more for premium. What I do is if I'm doing a mostly interstate run with the cruise control on, I run 87. If I'm going to have fun on curvy, hilly roads, I run premium.
 

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Anyone know how long it takes for the car to adust to the different octane levels? I'd have to assume that the computer gradually increases parameters with higher octane. Seems my car progressively felt better for the first few tanks after the dealer filled it presumably with 87 octane.
I'd think that if you go from 93 to 87 that the car senses knock in that direction and pulls timing quickly.
 

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You can safely run 87 octane in a stock ST. My observation is that it does not work very well in extremely hot summer weather. At 100ish degrees, so much timing is pulled the engine stops pulling for a second whenever you get into the boost more than a few psi. At lower temps my posterior dyno can't tell the difference between 87 and 93. So I run premium for a couple of hot months of the year and mostly regular when's temps stay below 70 or so. Stock '14.
 

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Anyone know how long it takes for the car to adjust to the different octane levels? I'd have to assume that the computer gradually increases parameters with higher octane. Seems my car progressively felt better for the first few tanks after the dealer filled it presumably with 87 octane.
I'd think that if you go from 93 to 87 that the car senses knock in that direction and pulls timing quickly.
The engine sensors are always adjusting.. Yes for lower octane the adjustment is near instantanious.
The preignition sensed immediately retards the spark.
(If you are on boost, you may suddenly get a 'hang' with a few revs of no ingnition. this is saving your engine from detonation)

On the other side, the engine management is always trying to advance the ignition.. it NEVER sleeps..
The ignition advance is always moving to the farthest advance with no pre knock.
So IMO in a few miles your engine is already optimized for the different octane (at the RPMs you are driving at!..
So if you have never revved the engine up, that first time it may 'be surprised' ..and you get the hiccup of a few rotations no spark flaw.)

I have only gotten the 'high rev on boost hiccup' when fooling around with part 87. When I run always 93.. it never happens
 

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If you track the car, drag it all the time, always running WOT on the highway, driving it like you stole it, you'll probably cause some damage long term because the car is always trying to find the edge of knock. You can run 87 or else Ford wouldn't spec it. It's just not the best. If you get a 93 or 91 tune, those are tuned to find the edge of knock way more aggressively than the stock tune and you will probably detonate within 10k miles possibly.

Reason why the turbo makes difference is you're running higher cylinder pressures than N/A. Octane rating is a rating that says how much the fuel can be compressed before it detonates without a spark. With N/A cylinder pressures aren't that high so it's not really a huge concern. On a K series Honda motor, they suggest 93, but you can run 87 for 200k and still not detonate. Running boost increases pressures in addition to heat at high revs leads to retarding timing because heat and pressure lead to earlier than desired ignition so the computer needs to compensate otherwise there will be knock and the engine will blow.
 

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Either E-85 with 91 mixture or just straight 91, never 87 or 89. 91 octane just provides better burn, plus cleaner, slightly even burning for all your car grilling needs. :cool2:
Less knock, less carbon build up on you're injectors and valves when using a higher octane.
 
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