[Canadian ST]

Ok maybe this is in my head but 2 tanks ago I put 91 octane in my car and I could swear it drives better. It seems smoother and has more power on the highway :blink: Is this true? I know the manual said to use 87 octane but I filled up again today with that sh@t and the car seems to be running slower? So would a 91 octane re-flash be even better?

[naz]

i think it is almost certainly in your head dude... the only way higher octane fuel offers more performance is if your ECU is setup be aggressive to advance timing and/or boost if no deto is seen... i'm like 99.9% sure that a stock focus ECU doesn't do that

the only advantage i can see for a stock focus using higher octane is that the fuel is cleaner and less likely to leave gunk in the fuel filter

as for whether a 91 octane flash is better.. on a stock focus i don't think it will make that much of a difference..

[NOS2Go4Me]

I'll go against you on that one, Naz. :P

I ran for a couple of days with 91 in my car with an otherwise identical setup (3" FS CAI, 2.5" MBRP flex-back) before the tune and the car was noticeably peppier than stock. After a reflash, it becomes a force of will to keep it under 4000 RPMs in 1st before the 1-2 upshift. And that's an auto ;)

It's too bad it's an "economy car" and not Ford's smallest performance vehicle anymore, because I wish they all came with a proper tune and 91-only requirements right from the factory.

As for mileage, 320KMs (and higher) is easily obtainable on 20L or so.

If you're going to keep the car Nathan, go nuts and get a flasher. It'll only serve you well in the short AND long run.

[NefCanuck]

another factor is that likely your local gas stations have all converted to 10% ethanol in the cheap stuff and 5% in the midgrade.

Ethanol and the Focus go together like crap on a stick. Even if I wasn't running a 91 tune, I'd probably be buying at least 89 grade to minimize ethanol stuff going through my engine <_<

NefCanuck

[Canadian ST]

"As for mileage, 320KMs (and higher) is easily obtainable on 20L or so."

"If you're going to keep the car Nathan, go nuts and get a flasher. It'll only serve you well in the short AND long run."


Hay Adam the re-flash is going to happen soon enouph, I want to lower the car first though. I did notice the gas mileage seemed to be a little better. I also noticed that the engine runs smother at idle and is "peppier on the highway"

[paolo]

I hope your filling up at ESSO. I got 91 octane for the price of 89. I had to do a double take to make sure my eyes were ok to verify if that was the actual Price I was SEEING and it WAS!

[CanadaSVT]

Canadian ST,Sep 20 2007, 08:26 PM Wrote:Ok maybe this is in my head but 2 tanks ago I put 91 octane in my car and I could swear it drives better. It seems smoother and has more power on the highway :blink:  Is this true? I know the manual said to use 87 octane but I filled up again today with that sh@t and the car seems to be running slower? So would a 91 octane re-flash be even better?
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You asked and IMO it's in yer head.

Isn't Sunoco 91 and Pioneer 91 the exact same and Pioneer costs less?

[CanadaSVT]

paolo,Sep 21 2007, 07:14 PM Wrote:I hope your filling up at ESSO. I got 91 octane for the price of 89.  I had to do a double take to make sure my eyes were ok to verify if that was the actual Price I was SEEING and it WAS!
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For some reason Esso makes my car literally stink out the ass, so I stay away.

[Canadian ST]

CanadaSVT,Sep 21 2007, 08:19 PM Wrote:

paolo,Sep 21 2007, 07:14 PM Wrote:I hope your filling up at ESSO. I got 91 octane for the price of 89.  I had to do a double take to make sure my eyes were ok to verify if that was the actual Price I was SEEING and it WAS!
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For some reason Esso makes my car literally stink out the ass, so I stay away.
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I used shell for the 91 octane. I guess if it good enouph for a Ferrari and my cars name starts with a f like Ferrari it should be ok. :P

[paolo]

CanadaSVT,Sep 21 2007, 08:19 PM Wrote:

paolo,Sep 21 2007, 07:14 PM Wrote:I hope your filling up at ESSO. I got 91 octane for the price of 89.  I had to do a double take to make sure my eyes were ok to verify if that was the actual Price I was SEEING and it WAS!
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For some reason Esso makes my car literally stink out the ass, so I stay away.
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I thoght Shell was the only bad gas to avoid? Essos been very good

[Canadian ST]

paolo,Sep 21 2007, 08:31 PM Wrote:

CanadaSVT,Sep 21 2007, 08:19 PM Wrote:

paolo,Sep 21 2007, 07:14 PM Wrote:I hope your filling up at ESSO. I got 91 octane for the price of 89.  I had to do a double take to make sure my eyes were ok to verify if that was the actual Price I was SEEING and it WAS!
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For some reason Esso makes my car literally stink out the ass, so I stay away.
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I thoght Shell was the only bad gas to avoid? Essos been very good
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Thats for the lower octane gas i've heard. for 91 its good

[mojoerally]

i use shell's 89 octane, and its been awesome. atm, i cant afford the 91 octane... but when i can, it will be used.

[darkpuppet]

Technically speaking, using 91 on a car engineered for 87 is just going to result in the air/fuel mixture burning slower and incompletely with the stock timing.

this can result in the build up of carbon and octane tolerance that will sooner 'chain' you to the 91 octane pump rather than give lasting performance.

When 91 can be beneficial is if your engine has built up carbon in the cylinders that provide sharp edges which results in hot spots that cause pre-ignition. This gets picked up by the knock sensor and timing gets pulled, killing performance.

Putting in 91 at this point in the car's life will help reduce the occurance of pre-ignitian, giving you back the timing that you lost with 87. But this is usually for very high mileage cars... and with proper maintenance, you shouldn't really ever have to go to 91.

So basically, putting in 91 prematurely is like teenage drinking, you're just going to have that much less liver when adulthood actually hits... i definitely wouldn't recommend it.

If your knock sensor pulling a lot of timing with 87, you may want to run some seafoam or something to help clean out the cylinders... and if you're going to run 91, you should really have a tune for it.

Ok.... also... depending on your mods, there are exceptions to this rule. -- IE, AEM and some other cold air intakes increas your car's horsepower by increasing the diameter of the MAF tube.

At part throttle, the car can compensate for the mild gain in diameter, but at full throttle, the car goes closed loop, and calculates the a/f assuming the old MAF transfer function. And at those loads, it'll exceed any loads you hit at part throttle, so you get no learning adjustments, and the mixture leans out and gives you horsepower increases.

Where does this put us?

Well, if you lean out the mixture under WOT using a CAI with larger-than-stock MAF tube, you could be experiencing pre-ignition and having timing pulled.. and putting in 91 will prevent that.

However, the car is going to lose power (comparatively speaking) to the points where 87 could be used without knocking (assuming a stock tune)... not to mention that your closed loop cruising is going to most likely experience lower fuel mileage.

My Experiences
I drove my focus 1500 km's in one day and made 4 gas stops, doing the 1st half with 87 and the second half with 91 With the tank filled (mostly) with 91 octane, I noticed a more than 100km drop per tank in mileage (approx 520km vs 650km) and the butt dyno picked up no horsepower gains.

I drove that length 1 week later in the other direction, filling up at the same gas stations, using 87 and 91 for the same legs I did going the other way, and the findings were about the same... 91 did nothing for the car -- mind you, it was < 1 year old at the time.

So there's my $0.02 ...

[snorcus]

87-91 I cant notice a difference on a stock tune.

[NikiterZTS]

butt dynos suck

[Spinal]

its probably time for a real dyno lol.

[NikiterZTS]

Spinal,Jan 10 2008, 07:12 PM Wrote:its probably time for a real dyno lol.
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well you just missed one last summer

[NefCanuck]

I ran 87 with a stock motor, added an MBRP exhaust then a Steeda SRI and now I run a 91 tune from FocusSport on my car.

While I do have documented evidence that adding the mechanical mods I did bumped up HP (From 108HP stock to 115HP) the revised 91 tune was the biggest gain in terms of power and driveability. The tune also meant a small fuel economy gain but only at steady state cruising, my best highway numbers are now 7.5L/100km (05 autobox)

I'll be doing a dyno test sometime this year to see how much more HP I've gained, but I would say I'm at 120HP now.

NefCanuck

[NikiterZTS]

^^i'll be looking at how much my car is stock :)

[SVTGuy02]

91 octane will do NOTHING for your cars that are tuned for 87.

And anyways.... why would you guys WANT to pay more for gas?!!? I drive an SVT, with a REQUIREMENT to get 91+ and it friggin sucks! Paying 10 cents more at the pump than everyone else blows chunks!

All that advertising bulls*** "run your engine cleaner and get more power, bla bla" is a buncha crap!

Octane rating is basicaly just the fuels ability to delay detonation.

Put low octane gas in a high compression engine, the heat of the compression with make the gas detonate prior to spark due to its LOW octane (low ability to delay detonation) versus putting higher octane gas in a high compression engine. The gas will be able to withstand the heat generated by the high compression in the engine due to its HIGH octane (high ability to delay detonation).

Read up what octane ratings are and stop listening to bulls*** advertising. All the gas stations want to do is f*** you anyways, why listen to them? ;)

Here is wikipedias definition:

Quote:The octane rating is a measure of the autoignition resistance of gasoline and other fuels used in spark-ignition internal combustion engines. It is a measure of anti-detonation of a gasoline or fuel.

So why put a slow burning fuel, in a car that needs a fast burning fuel? logic people.... logic!!