# Octane Level



## jblackburn (Apr 14, 2012)

Yes, run midgrade or premium in it. Mine runs like crap on 87.

You'll notice better and more consistent low-end power delivery and slightly better MPG.


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## ProDigit (Aug 31, 2015)

I run on 87 oct fuel, near sea level, and it runs very good when the outside temps are between 68 and 75F.
The difference between 87 and 89 or 91 aren't noticeable, but premium fuel 93 oct, does run better (more MPG). But I personally tend to believe it has more to do with the additive package, than the octane rating of the fuel itself.

Back to 87 oct,
There's a mild reduction in performance, barely noticeable, when temps rise above 80F, and a noticeable decrease in performance at 90F, but the car is still rideable.
From 95-100F the engine really lacks performance, and if the temps are hotter than 100F, you wished you had put higher octane fuel in the car.
At 100F, it takes the turbo nearly 750-1000Rpm higher to start boosting, and acceleration on the on ramp of a highway is slow.
At over 105-110F, with 87oct fuel, you can't accelerate in 6th, and need to shift to 5th to overtake someone, and I'm always fearful to surpass 80mph. But thankfully, before the engine decides to blow the piston, and created knock, the turbo starts kicking in, giving it just enough power to maintain speeds in 6th gear.

So, I would say, for any temp under 90f, the standard 87 oct fuel is good enough for driving the streets


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## obermd (Mar 3, 2012)

Octane is a measure of resistance to pre-detonation. Higher octane is more resistant. The Cruze uses a dual ignition timing map system where the low octane map pulls timing to protect the engine and the high octane map uses an aggressive ignition timing. The high octane map results in 3-5% better fuel economy depending on the model year and what TSBs have been applied to the ECU programming. Note, these maps don't measure octane directly. Instead the ECU actively monitors for knock and if it sees too much knock it drops back to the low octane map to protect the engine. The car always starts with the high octane map active but once it switches to the low octane map it apparently won't switch back until you turn the car off and then back on.

Many members here have found that 89 octane will keep their cars from dropping back to the low octane map.

ProDigit's assessment of how the car performs on 87 octane is accurate with one exception. As you go higher in altitude those temperatures he's reporting drop dramatically. I found my ECO MT needed 91 octane as soon as the outside temperatures exceeded 65F at the 5,000 to 6,000 elevations I routinely drive.

Another note - the Gen 1 Cruze (all trims including LS) have a KRD code, which means the car's engine is designed for 91 octane. The ability to run 87 is only through the above knock monitoring and dual ignition timing map.

I'm not sure if the Gen 2 Cruze's engine is also a 91 octane engine with the same protection software.


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## jblackburn (Apr 14, 2012)

> ProDigit's assessment of how the car performs on 87 octane is accurate with one exception. As you go higher in altitude those temperatures he's reporting drop dramatically. I found my ECO MT needed 91 octane as soon as the outside temperatures exceeded 65F at the 5,000 to 6,000 elevations I routinely drive.


Same was true for my Gen 1 @ sea level. Over 60 with 87 in the tank...nope. Couldn't get out of its own way.



> I'm not sure if the Gen 2 Cruze's engine is also a 91 octane engine with the same protection software.


Yes, sure feels like it.


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## neile300c (Jul 8, 2014)

I ran 87 Tier 1 in my Gen 1, tried 89 and 93, never felt a difference. 
Same thing with my Gen 2, until recently. I ran 3 tanks of 93 Shell in a row, and then accidently put Shell 87 in it. My theory was to run 93 for a month, and then see if i felt a difference. I filled it up with 87, and then I started feeling like the car ran a little rough, and sluggish. I don't know if I'm imagining things, but I put 93 back in it, and have not seen any issues.


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## ProDigit (Aug 31, 2015)

Also, one of the reasons my car feels a lot better at 75F or below, is because I'm running it without AC.
The AC eats about 10% of MPG on the highways. Not sure how it affects MPG in lower gears; but running a car with the ac draining your HP, does make it a bit more sluggish.
Most of the time, the Cruze runs fine without AC. But on hotter temps, running 87 octane, I do sometimes turn off the AC, just to have sufficient performance for overtaking or going uphill. 

I've read somewhere with regular fuel, and in hotter temperatures, that the 148HP cruze, puts out less than 97HP on the wheels, and I think I can believe that.
Running it on 87 octane in summer, very much reminds me of driving a 1969 volkswagen beetle.


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