# Safe to use 'Regular'?



## BadBowtie (Apr 18, 2015)

Check your Owners Manual !


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## jblackburn (Apr 14, 2012)

Most of the knock occurs at low RPM on these motors where the turbo starts to spool and make low end torque but there’s a zone where knock is likely. (Low speed pre ignition). It’s a combination of oil quality/additives and your fuel's resistance to pre ignition.

So do with that what you will.

Supposedly there’s an ECM/TCM update that will drop gears to let the engine rev a little bit more to keep it out of that LSPI zone under heavy load, like climbing a hill.


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## snowwy66 (Nov 5, 2017)

Owners manuals have recommended 87 since the beginning of time.

Those of you in the flatlands don't have anything lower then 87. Or is there?

It's 85 in the western mountains.


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## thebac (Jul 29, 2017)

IMO, you're fine with 87. 

Sent from my SM-G986U using Tapatalk


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## Johnny B (Jun 4, 2019)

IMHO the best medicine for LSPI is run the new Dexos Gen 2 oil, and make sure its also GF-6A and SP rated.


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## snowwy66 (Nov 5, 2017)

Dexos2 is diesel oil. Isn't it?


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## jblackburn (Apr 14, 2012)

snowwy66 said:


> Dexos2 is diesel oil. Isn't it?


Yes. But Dexos 1 Gen 2 is the updated gasoline oil spec for GMs turbo GDI engines.


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## snowwy66 (Nov 5, 2017)

jblackburn said:


> Yes. But Dexos 1 Gen 2 is the updated gasoline oil spec for GMs turbo GDI engines.


My comment was in reference to the above post who says dexos 2. lol


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## jblackburn (Apr 14, 2012)

snowwy66 said:


> My comment was in reference to the above post who says dexos 2. lol


It says Dexos Gen 2, just left out the "1"


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## Barry Allen (Apr 18, 2018)

BadBowtie said:


> Check your Owners Manual !


The owner's manual says 87 octane but one of the RPO codes says 91 octane recommended.

You would do best to run mid-grade if it's affordable and premium if it's not an outrageous cost.


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## BadBowtie (Apr 18, 2015)

Barry Allen said:


> The owner's manual says 87 octane but one of the RPO codes says 91 octane recommended.
> 
> You would do best to run mid-grade if it's affordable and premium if it's not an outrageous cost.


Regular Production Option (_RPO_) _codes_ that are available on the vehicle "RECOMMEND" 91 octane but the Owners Manual says 87 octane is Okay.. ??
I wonder why such a big difference ??

I agree that something in-between (mid-grade) would probably be best .. (if premium can't be afforded).
These cars perform better with good gas.


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## Barry Allen (Apr 18, 2018)

BadBowtie said:


> I wonder why such a big difference ??


GM does not want to sell an economy car that "recommends" premium unleaded. 

Selling _ANY_ car that recommends or requires premium unleaded is a huge turn-off to a huge percentage of the buying public. If you're an upmarket car brand, you can get away with it because most buyers have money to spare - someone buying an Audi or a Porsche knows what they are getting into.

It's not a terrible thing to use premium unleaded. If your fuel economy drops when using 87 octane, the price increase on a per-gallon basis can be recovered with better fuel economy. But if you live somewhere that it's not cheap (one gas station in a smaller town near me had regular unleaded for $3.15, Diesel Fuel for $3.19, and premium unleaded for $4.19! Over a $1 more per gallon is a bitter pill to swallow for most buyers.

The Cruze was trying to compete with the Civics and Corollas and a few other players (Hyundai Elantra, Nissan Sentra, etc.) in the basic economy car market. In the 2nd generation cars, it was 100% turbocharged engines. If GM had marketed the car with premium recommended, it would have been a harder sell. I mean, fewer people were already buying the cars and they quit making them because of this, so it's already a discontinued model.

One thing I noticed when glancing at a new Corolla is that the engine in that car has some sky-high compression ratio to deliver about 170 horsepower without a turbocharger. That engine is 13:1 compression ratio! The only way Toyota is getting away with using regular unleaded int hat engine is some ignition timing tricks that probably makes the car sluggish - torque figures aren't anything about about 150 foot-pounds. It's a shame they can't make that engine run on E85 fuel. The higher octane from that would do wonders for power and efficiency. It makes me wonder if running premium unleaded in that engine runs better than regular.


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## jblackburn (Apr 14, 2012)

Barry Allen said:


> One thing I noticed when glancing at a new Corolla is that the engine in that car has some sky-high compression ratio to deliver about 170 horsepower without a turbocharger. That engine is 13:1 compression ratio! The only way Toyota is getting away with using regular unleaded int hat engine is some ignition timing tricks that probably makes the car sluggish - torque figures aren't anything about about 150 foot-pounds. It's a shame they can't make that engine run on E85 fuel. The higher octane from that would do wonders for power and efficiency. It makes me wonder if running premium unleaded in that engine runs better than regular.


Most NA GDI engines these days have pretty high compression ratios. Like the Mazda SkyActiv (13:1 - 14:1 depending on the engine), Hyundai 2.5 (13:1), Toyota's other "Dynamic Force" engines like the 2.5 (13:1), or GM's 2.5/3.6 (11.5:1)

Combined with a long stroke that most manufacturers use for low-end torque, it does make for a pretty coarse, gritty-sounding engine though.


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## Barry Allen (Apr 18, 2018)

jblackburn said:


> Mazda SkyActiv (13:1 - 14:1 depending on the engine)


*"Skyactiv-G engines for the U.S. market have a lower compression ratio of 13:1 allowing them to operate on standard instead of premium fuel with an approximate 3-5 percent reduction in torque and fuel economy."*

Mazda brought it down for the US market because, get this, they don't want to try selling cars that require PREMIUM unleaded. LMAO


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## jblackburn (Apr 14, 2012)

Barry Allen said:


> *"Skyactiv-G engines for the U.S. market have a lower compression ratio of 13:1 allowing them to operate on standard instead of premium fuel with an approximate 3-5 percent reduction in torque and fuel economy."*
> 
> Mazda brought it down for the US market because, get this, they don't want to try selling cars that require PREMIUM unleaded. LMAO


Yep, checks out.

The Skyactiv-X bumps that to 16:1, though. Lean burn compression-ignition gasoline engine (under certain conditions), pretty neat.

I think they're struggling a bit with that one to make it perform well for the US market AND deliver good power/refinement on 87 AND meet US emissions requirements, which is why it hasn't been widely adapted yet. That, and we want more power than the 2.0L mill in a CX-5 too - the original 2.0L CX-5 was hugely underpowered for US traffic.


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## snowwy66 (Nov 5, 2017)

Anybody know the compression ratio and power output for my 76 vega.?


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## jblackburn (Apr 14, 2012)

snowwy66 said:


> Anybody know the compression ratio and power output for my 76 vega.?


Vega? Factory compression range: Yes. 

Until it overheats.


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## Barry Allen (Apr 18, 2018)

jblackburn said:


> The Skyactiv-X bumps that to 16:1, though. Lean burn compression-ignition gasoline engine (under certain conditions), pretty neat.
> 
> I think they're struggling a bit with that one to make it perform well for the US market AND deliver good power/refinement on 87 AND meet US emissions requirements, which is why it hasn't been widely adapted yet. That, and we want more power than the 2.0L mill in a CX-5 too - the original 2.0L CX-5 was hugely underpowered for US traffic.


I spent years waiting for a Mazda 6 sedan with a Diesel engine and 6-speed manual transmission. Sometime around 2010 (maybe 2012?) it was teased that it was coming. I waited. And I waited. And I waited. 

Mazda kept on trying to get the Diesel engine tuned to meet US emissions without urea injection "Because VW was able to do it" and then Dieselgate broke. The silence at Mazda management meetings must have been awkward after all those years of engineering telling management they were trying to get it done.

Mazda finally brought a Diesel engine to the CX-5 and it was $40,000 and doesn't even get decent fuel economy. Then, after selling about 1,000, they killed it and it's done for good in the USA.

I would have loved to get a Mazda car with a Diesel engine if I could have tuned it to match the power and economy offered in overseas markets, but it can't be had at any price here.


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## 17Hatch6MT (Dec 28, 2015)

I don't drive many miles, the car gets great fuel economy, I can afford the premium. Like the power being there when I want it too, which won't always happen with lower grade fuel. Thanks for the input!


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## Barry Allen (Apr 18, 2018)

jblackburn said:


> I think they're struggling a bit with that one to make it perform well for the US market AND deliver good power/refinement on 87


For what it's worth, there has been a not-well-known movement to have oil refineries transition to 89 octane being the new "regular unleaded" in the USA. With the movement to high-compression GDI engines and more turbocharged engines, the fuel economy benefits could be there if we would adopt higher octane fuels as the baseline standard across the USA and have engines tuned to take advantage of that.


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## jblackburn (Apr 14, 2012)

Barry Allen said:


> For what it's worth, there has been a not-well-known movement to have oil refineries transition to 89 octane being the new "regular unleaded" in the USA. With the movement to high-compression GDI engines and more turbocharged engines, the fuel economy benefits could be there if we would adopt higher octane fuels as the baseline standard across the USA and have engines tuned to take advantage of that.


I've had several port-injected N/A engines that even see a benefit on higher octane. 89 is usually enough for those.

There are a smattering of N/A engines out there actually recommending more than 87 now not in luxury brands.


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## Barry Allen (Apr 18, 2018)

jblackburn said:


> I've had several port-injected N/A engines that even see a benefit on higher octane. 89 is usually enough for those.
> 
> There are a smattering of N/A engines out there actually recommending more than 87 now not in luxury brands.


If I remember, the group was some manufacturers who low-key wanted the oil refiners to make 89-90 octane the new "regular" and then 93 octane as premium. Doing this could eliminate mid-grade, which is a product not offered at some stations and is something I've never once seen anyone purchase at any point in my life unless regular 87 octane was sold out and they needed gas right at that minute.


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## 6Speed2016LT (Jun 14, 2016)

Barry Allen said:


> If I remember, the group was some manufacturers who low-key wanted the oil refiners to make 89-90 octane the new "regular" and then 93 octane as premium. Doing this could eliminate mid-grade, which is a product not offered at some stations and is something I've never once seen anyone purchase at any point in my life unless regular 87 octane was sold out and they needed gas right at that minute.


In most parts of Canada we have 5 choices at the pumps depending on the station....87, 89, 91, 93 and 94....

As per the advice of Barry and many other knowledgeable members on here...during cooler months you can pretty much stick to the lower/mid grade fuels. For the small amount of dollars it costs to go from 87 to 89, I usually stick with 89 myself. Once the temp gets hot....June, July and August kinda thing..I do put in 94 to help prevent LSPI.
My Cruze is going on 6 years old soon...(gen 2) No issues with the clutch (slave cylinder), no issues with LSPI.

I firmly believe looking after your car right and using the advice of knowledgeable members here has helped save me from potential issues.....

Cheap insurance...

Jason


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## Barry Allen (Apr 18, 2018)

I found the article I was remembering: https://www.eesi.org/articles/view/...ing-of-u.s.-gasoline-for-bump-in-fuel-efficie

The recommendation is to have 91 octane as "regular unleaded" in the USA.


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## johntroyer3 (Jan 12, 2022)

What about using regular ethanol free pure gas?


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## jblackburn (Apr 14, 2012)

johntroyer3 said:


> What about using regular ethanol free pure gas?


Low octane = knock.


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## Barry Allen (Apr 18, 2018)

johntroyer3 said:


> What about using regular ethanol free pure gas?


Never.

89 octane or higher in cold to moderate weather, 91 octane or higher in warm or hot weather.


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