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1.4L Ecotec Turbo I4

Premium Fuel?


This is a discussion onPremium Fuel? within the 1.4L Ecotec Turbo I4 forums, part of the Engine and Performance | Cruze Forumz category!
I've seen others with the ECO version running premium and getting significantly improved fuel economy. That said, I was curious ...

138HP | 148 lbft 1.4L Turbo Ecotec Engine Discussion


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Old 02-22-2013, 12:23 PM   #1
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Default Premium Fuel?

I've seen others with the ECO version running premium and getting significantly improved fuel economy. That said, I was curious about trying either midgrade or premium to see if it improved fuel economy in the 1.4L Ecotec Turbo. The manual states to "use regular unleaded gasoline with a posted octane rating of 87 or higher". It does mention running higher if there is knocking, which is not my case; I'm interested purely for any gains in fuel economy. It does not mention anything about not running a higher octane, so is there any reason I shouldn't?

Anybody have experience with running a higher octane in the 1.4L and, if so, what were the improvements, if any?
*I run premium (93 octane) in my Monte Carlo but it's recommended for the LS4 V8; stated in the manual.
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Old 02-22-2013, 01:16 PM   #2
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Do you have a ScanGauge-II™ or something similar (OBD-II bus reader)? If you do, then you can "test" your hypothesis yourself by checking ignition advance degree readings on each octane while driving over the same roadway.

If you find the ECM consistently applys more advance on the 93 octane fuel than you saw on the 87 octane, that's a good indication you're getting more POWER. Fuel economy should improve too, but octane is not the same as energy content (BTU's), which varies little, except for the summer vs. winter blend differences.

Unfortunately, these "tests" will be impossible to do back-to-back (ie: A-B-A) because you have to empty the tank each time. However, you can shorten the turn-around cycle by running the tank down almost to empty (let the lamp come on) on 87 octane--do your test--then fill-up with 93 octane and repeat the test...but that'll only be half of the desired scientific A-B-A test methodology. Also, all the old fuel already in the fuel system plumbing must be used up before the new fuel effects will become detectable.

A mixture of 2 gallons of 87 octane combined with 13.6 gallons of 93 octane is a mixture ratio of 87%...but should be 'close enuf.'
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Old 02-22-2013, 02:34 PM   #3
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Quote:
Originally Posted by 70AARCUDA View Post
Do you have a ScanGauge-II™ or something similar?
I do not have one that I'm aware of.

I'm thinking, sometime in the next three months, of trying at least three tanks back-to-back of premium (93 octane in Michigan). Running at least three should account for the remaining regular that is left in the tank/fuel system on the first tank of premium, like you mentioned, as well as give me a good average. The only way I would stick with running the premium is if I find that it's cost effective; i.e. the mileage increase, if any, makes up for the additional ~$2.20 spent on premium over regular. If not I can always try midgrade.

I'll keep everyone posted.
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Old 02-23-2013, 11:18 AM   #4
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Another thing to add.

Switching from running regular to premium in the Monte Carlo didn't show any noticeable gains in fuel economy, although I'm running a high performance air intake and exhaust system in that car so the engine is pulling in and exhausting more air. More air means the system wants to throw more gas into the engine to keep the air/fuel ratio the same. Although no gains in economy, the premium did slightly increase performance.
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Old 02-23-2013, 11:47 AM   #5
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...speaking of "...more air...", remember, the turbo actually 'dumps' any excess air that the ECM decides isn't necessary...so without tweeking the ECM's programming (ie: a "tune" job) the 1.4LT could--likewise--be considered "maxed out."
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Old 03-14-2013, 11:23 PM   #6
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I'm still hovering right around 27.5 mpg on regular 87 octane right now and that's at about 65-70% highway driving.
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Old 03-24-2013, 12:56 PM   #7
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I find that the difference in MPG when using higher octane becomes more apparent with more displacement. The larger American V8's I find will gain 10-15 HP with higher octane fuel. That extra power through the RPM range technically could allow the engine to operate more efficiently if you don't need to get in to the pedal as much to achieve your desired speed.

However, a .5mpg gain when you're getting 27mpg is negligible vs. a large V8 getting 12-15mpg it's pretty significant and (maybe?) worth the extra coin.
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Old 03-27-2013, 10:14 PM   #8
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I do agree, the higher the mileage the less a .5mpg savings is going to show at each fill up. Although, I am still a bit curious with the Cruze.

I could feel it a tiny improvement in performance going to premium in the Monte Carlo. The engine (5.3L LS4 V8) just runs a bit better overall. I'm usually in the pedal half the time with that car, so that and the fact that I'm moving more air through the engine with my current setup doesn't show any real mileage gains. I average about 17-18mpg with that car and that's mostly (70%) city driving.
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Old 03-28-2013, 02:12 PM   #9
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The REAL difference between the 5.3L LS4 V8 and the 1.4LT is their respective 'sensitivities' to knock (the CAUSE) and its attendent amount of 'knock retard' (the EFFECT).

The V8 is a constant compression engine but the turbocharger makes the 1.4 a "variable compression" engine. Hence, the V8 ECM typically (depending upon fuel quality, ie: octane value) isn't constantly 'fighting' between optimum spark-advance and too much advance, which is exactly what happens when the turbo spools up on the 1.4LT and starts pumping air into the engine--effectively pushing the static CR of 9.5:1 up to as much as 22:1. And, that increased CR needs a higher octane level or the engine begins knocking (mild) or dentonating (extreme) instead of smoothly "burning" its A/F-mixture.

This is why using higher octane fuel in a turbocharged engine almost always produces both more POWER and better fuel ECONOMY, because the engine ECM can advance the timing to extract MORE power from the fuel under load without damaging the engine. Conversely, using a lower octane fuel won't *hurt* the engine because the engine ECM will constantly "pull" timing to keep knocking from occuring, but in doing so, both the power (significantly) and fuel economy (slightly) are reduced.
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Old 04-17-2013, 10:36 AM   #10
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CUDA, that's a great explanation.

I do have an update. I DID refuel with premium recently and went through my first tank on it. That first fill-up with premium was 11.25 gallons, so about 3/4 of the tank after refueling was premium.

Doing some comparing, since I purchased the car, on seven tanks of regular I have run an average of 27.7mpg. My first tank on premium I got 29.8mpg, so about 2mpg better than my overall average on regular and 0.8mpg better than my previous best, which was also on regular. I'll run premium for a while so I can get a running average on it and go from there. So far it looks like it may pay off, but I'm not going to get ahead of myself. I do notice a slight performance improvement which is nice.
Just to note, my previous best was 29.0mpg (on regular) and that was on the very first tank I went through from the dealership. That drive home from the dealership was mostly higher speed main roads and highway, plus I was driving slow(er) because it was through a blizzard.
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