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I live in Lubbock, TX where regular gas is 86 and mid is 88 and premium is like 91. I know the manual says 87 minimum but if I can save 0.20/gal at the pump I'd like to. This is my first time with a turbo car
 

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To avoid causing any damage, I'd highly recommend using no less than 87.

Boring explanation of why:
Octane ratings are the resistance to pre-detonation or what's known as pinging/knocking. This occurs when the air/fuel mix heats up too much and reaches the point of spontaneous combustion on the compression stroke before the spark plug ignites it at the optimal time. Vehicles with high compression ratios or forced induction (turbo or superchargers) require a higher pre-detonation resistant gasoline. The Cruze has sensors that monitor knocking and will retard the timing if it is given 87 octane, but this causes lower fuel economy and less power since it can't run at the optimal timing advance.

The Cruze has forced induction and would prefer to have 93/91 fuel especially in high heat or when using the AC. The inter-cooler (cools the air back down after it gets compressed in the turbo and heats up) is sandwiched in between the coolant radiator and the AC radiator. When you're running low octane while driving in hot temperatures or using the AC the air intake temperature is much higher so the air/fuel mix is much more likely to pre-detonate in the cylinder during the compression stroke and if the computers can't retard the timing enough it will cause harm to the engine.

I've noticed when I run 87 my engine is less responsive and feels less powerful because it's pulling timing(I can monitor my timing advance on my ultra-gauge), I have to down shift on hills much more often or when accelerating in 6th, and I get much worse fuel economy which negates the savings in fuel. If you insist on running the cheapest fuel I advise strongly following the manual's suggestions and put no less than top tier 87 in the tank.
 

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Discussion Starter #3
I noticed nothing in the manual says anything about higher octane gas other than do not go below 87. What I filled today was 88 octane. Has anyone on here tested the different octanes?
 

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Speaking from experience (Denver) - use at least the 88 octane. Give the 91 a try as well.
 

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The short of it, while the car will run on the minimum octane, you may find that spending $2.50 a fill-up to be one of the cheapest, most effective performance boost you can find.
 
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Discussion Starter #7
obermd, did you see much difference in the mid grade in Colorado vs the premium? I do recall being on a trip with my dad to Colorado in what is now my brother's Cruze and knowing we were about to go back to Texas so we filled with mid grade to get 87 for Texas. I'm about 3500 ft above sea level in Lubbock so I still get reduced octane.

When at sea level should I still use higher grade for the turbo?
 

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obermd, did you see much difference in the mid grade in Colorado vs the premium? I do recall being on a trip with my dad to Colorado in what is now my brother's Cruze and knowing we were about to go back to Texas so we filled with mid grade to get 87 for Texas. I'm about 3500 ft above sea level in Lubbock so I still get reduced octane.

When at sea level should I still use higher grade for the turbo?

I run only 91 or higher octane. Lubbock is flat. Denver isn't. With any octane lower than 91 my car pulls timing to the point where it feels like the clutch is slipping when I'm climbing. The other consideration is heat - Edmunds Automotive performed a 3,000+ mile test with a 2011 LTZ and discovered that 91 octane resulted in enough difference that even with the 30-40 cent per gallon price increase it was cheaper to drive the car on 91 octane. They ran their test from LA to Arizona (~5,500 ft above sea level) and back during the summer heat.

Bottom line - run two full tanks of each grade of fuel and then pick the grade that gives you the least throttle pulsing under load. If you're ok with some throttle pulsing you can potentially save a little money at the tank by running a lower octane. What you don't want is such a low octane that you feel heavy throttle pulsation while accelerating.
 
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