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Well yesterday with my 2012 1.4l turbo I went ahead and used the 91 premium gas instead of the 87 with everything stock and no performance tune here in Southern California. I noticed since it was getting warmer I was getting 34mpg instead of my usual 37-38mpg and I will report just after a 100mile drive my mpg increase slightly by 0.4 but the engine was so smooth. There was no more hesitation or lag, the car was pretty. Next fill up I am going to try the 89 to see if there is any deviation from the 91. But as of right now, I will be ditching the 87 octane.
 

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Next fill up I am going to try the 89 to see if there is any deviation from the 91. But as of right now, I will be ditching the 87 octane.
If your 2012 is anything like mine, it runs just ok on 89 octane. I definitely notice a power decrease on 89 octane when I need it most(higher RPM). No more octane experiments for me 91/93 octane only for my cruze, even though my car is and will remain all stock.
 

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If your 2012 is anything like mine, it runs just ok on 89 octane. I definitely notice a power decrease on 89 octane when I need it most(higher RPM). No more octane experiments for me 91/93 octane only for my cruze, even though my car is and will remain all stock.
I came to the same conclusion last winter. I run 91 year round.
 

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I only run the cheap stuff 87 all winter long . why you ask , I only drive city Miles all winter long and any benifits from a higher octane would be pointless and noncost affective in 45 mph Zones .. that are like crawling zones on any given day when the Masses forget how to drive , or Black Ice Days which we have had more than a few of this season .
 

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Update on my turbo with the 91 octane I am getting 40mpg and it's super smooth. I guess it seems 91 is the best for the California whether and the Long freeway driving I do.
 

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It doesn't wait until full-on knock... There are different levels of knock, and it advances the timing to light knock, then backs it off, then tests it again, etc... The light knock that it brings it up to doesn't have anywhere near high enough pressure spike to break down the hydrodynamic bearing and cause metal on metal contact, or to hole a piston or anything. It still does this with any grade of gasoline, up to a point, to always be getting the maximum amount of timing advance for the gasoline it's running.

It does this all the time, as have most vehicles for the last 20 years... The Grand nationals, and all of the regular 3.8L engines, and CPI Vortec engines have done this, as well... My friend's dad's Grand National has had nothing but 87 in it from day 1, and blew a head gasket after 265,000 hard miles (with it being 3 boys' high school car)...

At least that's what I learned when doing my Engineering specialization in automotive electronic control...

Mike
I find that very hard to believe about your friends dad's Grand National, only running 87 octane didn't pop a head gasket much earlier. They weren't running a larger intercooler or alky injection were they. I have seen guys pop head gaskets running 93, in an unmolested GN - stock. However, it was a hot day at Milan Dragway and the guys had made around 5 passes.
On the flip side, my Grand National is running an after turbo and 25psi of boost. I run 93 with a PAC alky injection system and my wideband O2 sensor went bad and my A/F ratio went very lean 12.8:1 and my old stock ECM and knock sensor retarded the timing and opened the wastegate, boost dropped quickly. It did it several times before I figured out it was my wideband O2 sensor was bad. The good thing, with the modification to my ECM I can turn off the WBO2 correction and just use the stock NBO2. Perhaps that is what saved your friends dad's Grand National. That is waste though, Grand Nationals, Type-T and Turbo Ts are getting rare. I hope they rebuilt or at least replaced the head gasket. Do you know if they were still running the original stock turbo? Typically the stock turbos start to die at around 140k miles, assuming they have only ran stock boost levels.
 

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FWIW, the turbo 3.8L Buick Regal, in the mid-late 1970's (before it was the T-Type or GN), even carburated, had a knock sensor and an ignition control box that was tuned for premium, but would run 87 just fine, with less power... Good friend of my dad's (another automotive engineer) ran his bone stock version on 87 for close to 200k miles, and it's still together... The only issue is that there were so few of them made in the late 70's, that GM stopped servicing them, so there are some parts that are specific to that car, that he can't get any more...

Same deal with all of the SFI Turbo 3.8L engines, and the MPFI 3.8L and 3800 Series I engines, as well as the "HO" 4.3L (CPI before it was called Vortec), all pre-OBDII...

Better computers make it more accurate and easier, but it can and has been done with much, much less...

Mike

Mike,
There is a lot of aftermarket support for the Grand National, T-Type and Turbo Ts(87). I own a GN and I have no trouble finding 3.8L or 4.1L blocks. A NA block 3.8L or 4.1L block can be used, all that needs to be done to the block is drill out and thread for a fitting for the oil return line from the turbo. Would you think that there is a shortage or the these block, but there isn't. There is also a company that makes the 3.8L and 4.1L performance blocks for the 84-87 Buick Turbo Regals.
 

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As stated earlier, during cold weather below freezing, it takes a lot of fuel to warm the engine up. I noticed my mileage drop considerably here in MI last winter. When the weather got too bad, I simply parked my Cruze and started driving my beater to work. However, I'm going to run 87 next time I feel up and see what happens. When it gets really cold, I will hook my engine heater. It attaches to the oil pan. See if that makes a difference in cold weather.
 

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Recently performed an experiment with my 2014 1lt auto 1.4l. 3 consecutive tanks of premium (93) followed by three consecutive tanks of regular. Similar drives, I commute about 100 miles a day mon-fri, and similar ambient temps (70-80 in the am; 80-95 in the afternoon). My results were somewhat surprising. I got slightly better economy using 93, but no where near the 10-20% some people here are claiming.

Three tank 93 average was 37.9 mpg, and three tank 87 average was 37.1. My butt dyno may not be as good as some peoples here but I really didn't notice any drivability issues. Considering that regular fuel around here is $2 a gal, and premium is about $2.50, I can't justify a 25% increased fuel cost for 3% better economy


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Recently performed an experiment with my 2014 1lt auto 1.4l. 3 consecutive tanks of premium (93) followed by three consecutive tanks of regular. Similar drives, I commute about 100 miles a day mon-fri, and similar ambient temps (70-80 in the am; 80-95 in the afternoon). My results were somewhat surprising. I got slightly better economy using 93, but no where near the 10-20% some people here are claiming.

Three tank 93 average was 37.9 mpg, and three tank 87 average was 37.1. My butt dyno may not be as good as some peoples here but I really didn't notice any drivability issues. Considering that regular fuel around here is $2 a gal, and premium is about $2.50, I can't justify a 25% increased fuel cost for 3% better economy


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That's interesting. They key here is that you have a 2014. They seem to have made some kind of programming change that stops the humongous performance dip using 87 vs 93. They're compensating some how in the software. But you still noticed a change in mileage, albeit not as big. Interesting.

Most people claiming performance castration on 87 (me included) are 2013 and lower model years, before the software was changed. Many of us have gotten 2014 rentals running 87 and noticed it running fine (although on mine I could definitely still feel some timing being pulled in 102*F)

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I sure have noticed my 1.4T runs better on high octane.
Yes, 2013 would be the year of huge gap between the 87 and KRD 91 fuel maps. I'm convinced my car had no 87 fuel map the way it hated 87.
 

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I'm going to consistently start running mid grade. If my numbers keep coming up around 50 mpg it will be worth it but ¢27 is a big jump. Basically a 9? price jump. Premium is ridiculously higher. 31% price increase vs 87. Doesn't make much sense if the car runs right. Even at 87 octane. Slightly retarded though lol. I can consistently get 45 mpg with 87 so no way I can recoup 31% in milage. 9% is possible 49.5 mpg no problem I believe my best tank just over 51 mpg was mid grade. Premium go recoup cost jump would be just shy of 59 mpg. Cost effective is what I'm going for. If your driving a Cruze you didn't intend to go for HP in the first place so no point in ponying up an extra ¢72 per gallon for a minimal performance boost. ATM 87 2.27 89 2.54 91 2.99 93 3.07. ¢80 more for 93 octane!!!
 

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My 2011 never see's improvement in MPG with octane increase and really shouldn't. Gas is gas in terms of energy, octane is a additive to prevent pre ignition or knock. If the engine is running close to peak then any octane increase won't figure in unless it was really dialing things back in 87 octane. If your results in MPG don't improve then I agree, why buy more expensive gas for very little return. GM engineered the engine for 87 octane so it doesn't hurt to try higher octane gas, and for some it may provide some viable improvements. But definitely premium near me is about .40 cents or higher than regular. Have to see significant improvement to justify premium.
 

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I have been running 89 in my 2015 with good results. Though my car does have a turbo, I would not consider it a performance car.
 
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