Premium gas for Skyactive?

[RayCJ]

Just found this "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."

Source: "Mazda Skyactiv-G and Skyactiv-D Engines in Detail". Caranddriver.com. Retrieved 13 July 2018. https://en.wikipedia.org/wiki/SkyActiv

"Premium Fuel, Mid-Grade Output

Premium, 91-octane fuel is required for the Sky's not-so-staggering 163 hp at 6000 rpm and 155 lb-ft at 4000, but Mazda is proud of its exceptionally wide torque band for enhanced real-world drivability. To enable running on regular gas, the U.S. version will have a compression ratio of 13:1, which means fuel economy and torque will diminish by about 3 to 5 percent, according to Mazda. The premium-fueled Sky we drove was perfectly adequate in the Mazda 6 prototypes, although acceleration was rather leisurely—far slower than the current Mazda 6 with its 168-hp, 2.5-liter—giving us plenty of time to wish for a bit more smoothness during the extended time in each gear. But being in the lighter Mazda 3 would help, and the tradeoff for near-diesel levels of fuel economy is probably worth it."

 

[PimTac]

Not sure how they got those numbers. HP on mine is 187 and torque is 186.

 

[RayCJ]

Originally Posted by PimTac
Not sure how they got those numbers. HP on mine is 187 and torque is 186.



Those numbers were cited for pre-production 14:1 engines. The significant issue seems to be that 13:1 was selected for North America because of the prevalence of low octane gasoline.

 

[PimTac]

Originally Posted by RayCJ
Originally Posted by PimTac
Not sure how they got those numbers. HP on mine is 187 and torque is 186.



Those numbers were cited for pre-production 14:1 engines. The significant issue seems to be that 13:1 was selected for North America because of the prevalence of low octane gasoline.




Which is not a huge deal. Mazda knee that requiring premium fuel would affect sales. Also, the engines have been going through CQI since they started production. Today's SkyActiv engines are different from the first ones in many ways.

 

[perfect_oil]

Originally Posted by RayCJ
Those numbers were cited for pre-production 14:1 engines. The significant issue seems to be that 13:1 was selected for North America because of the prevalence of low octane gasoline.


How they manage to get an engine to run on 87 octane fuel with a high compression ratio of 13:1 is a small miracle all to itself. In the old days of the American muscle car era, that wouldn't be possible without 108 octane or whatever the highest octane rating was available at the time.

 

[Ded Mazai]

It depends on how long you want to keep the car. The car was designed for octane 93 but the manufacturer leaves you freedom to choose the octane number you want. The only gas in Canada worth considering is Shell 91. Or Shell 89 if you don't care much about the car.

 

[tundraotto]

Originally Posted by Ded Mazai
It depends on how long you want to keep the car. The car was designed for octane 93 but the manufacturer leaves you freedom to choose the octane number you want. The only gas in Canada worth considering is Shell 91. Or Shell 89 if you don't care much about the car.


The anti-knock system is maybe more sophisticated than any other mass-produced engine design....saying using a lower octane would cause lower engine life-expectancy is completely unfounded.

 

[ndfergy]

I've posted this before

 

[atikovi]

Originally Posted by perfect_oil
Originally Posted by RayCJ
Those numbers were cited for pre-production 14:1 engines. The significant issue seems to be that 13:1 was selected for North America because of the prevalence of low octane gasoline.


How they manage to get an engine to run on 87 octane fuel with a high compression ratio of 13:1 is a small miracle all to itself. In the old days of the American muscle car era, that wouldn't be possible without 108 octane or whatever the highest octane rating was available at the time.


Direct injection. Lowers intake charge temperature allowing lower octane fuel to run satisfactorily.

 

[bobdoo]

I run Premium in my CX-5 so that my infrequent trip usage doesn't build up water in the lesser grades alky blend.

I have posted a UOA prior for the poster who mentioned it.

 

[bobdoo]

Originally Posted by ndfergy
I've posted this before




The mechanic is *surprised* that it takes the exact same HP to move the dyno at 50MPH, regardless of fuel...
OMG, I've lost a few IQ points watching that.

 

[fusseli]

SO has a 2019 3 2.5L. Manual says 87. Use 87! Simple as that.

 

[billt460]

Originally Posted by Dwight_Frye
I have a 2019 CX 5 with the 2.5 liter turbo Skyactive engine, The manual states that the car makes 227 HP with 87 octane and 250 HP with 93 octane......

If you feel burning Premium is worth an additional 23 horsepower in a 4 cylinder turbocharged engine, there is your answer right there.

 

[Ded Mazai]

Originally Posted by bobdoo



The mechanic is *surprised* that it takes the exact same HP to move the dyno at 50MPH, regardless of fuel...
OMG, I've lost a few IQ points watching that.


They don't know what they are doing. Looks like they were told to make a video about gas and this is what they've come up with. And even if the tests were valid they shouldn't switch fuel like this because it takes at least 15-20 minutes for the computer to adjust to the new octane number.

 

[Eddie]

I have a 2014 CX5 Skyactiv 2.5L DI engine. I have kept very accurate fuel consumption values for over 1,500 miles on 87 vs 93 octane fuel. The tank to tank variability is such that any difference is lost. In addition; I felt no difference engine smoothness and difference in acceleration is only subjective in my case. Therefore, 87 is the best for my NA 2.5L engine. Ed

 

[Ws6]

Originally Posted by wolf_06
Gooday,

I purchased a new 2018 Mazda 3 GS auto with the 2.0 Skyactive engine. I am very happy with the car, I have 20k km on it, very good fuel economy.

Some people say I should run premium fuel be ause of the direct injection in the Skyactive engine.

Is there any benefits for running premium fuel for Mazda's Skyactive technology?

Thank you!

I ran 87 for over 100k miles. No issue.

 

[bbhero]

Would you know how they managed to run a motor that is 13:1 compression on 87 effectively ??

ECM... Have a lot to do with that I am guessing... What else??

I am just curious how they could do that... And I think maybe you would have a good answer.

 

[billt460]

Originally Posted by bbhero
Would you know how they managed to run a motor that is 13:1 compression on 87 effectively ??

The computer detunes the engine so it can run on that crap, and not knock, and / or detonate itself to death. This is why the whole argument that burning Premium gas is a waste of money, is really not totally applicable today. These modern engines have sky high compression ratios.

The only way they can run on 87 Octane fuel without knocking harder than a UPS driver who's running late, is to reduce the performance of that engine to the point it doesn't damage itself. The result is less performance and worse fuel mileage. There really is no way around this.

In 1968, long before computers in cars, the ZL-1 Corvette ran a 12.5 to 1 compression ratio in it's all Aluminum 427 race engine. It was barely street able. It required the highest octane fuel available at the time. The Skyactiv-G runs 14 to 1. It can run on 87 because today we have computerized ignition and fuel injection systems that detune the engine to allow it. But it does so with less horsepower, as the manual states. Chrysler's 5.7 HEMI V-8 is similar. It will run on 87 without any problems. But it won't deliver the maximum advertised horsepower.

The bottom line is if you want to extract the best performance and mileage from your engine, you have to run higher octane fuel to do it. You can argue it's not worth it due to cost, and you might be right. Especially for everyday, driving to and from work, and to the grocery store.

But it doesn't change the fact that to get the most performance you have to. Back in the 60's you had to, regardless if you wanted to or not. Because the result if you didn't was most likely a damaged engine. With variable compression engines just around the corner, the ability to burn cheaper, lower octane fuel will most likely increase even more.

 

[RayCJ]

In the case of Mazda, they use all the standard techniques (VVTi and VVTe etc) and they improved and optimized everything. Also, they made huge gains by totally exploring and analyzing the combustion process. They analyzed both theoretically and by direct observation (with some pretty cool technology) how fuel burns in a cylinder. They also came to realize that fuel needs to be burned differently under varying engine load. The system has multiple modes of fuel injection and it can gradually transition between modes as needed. In some cases a small amount of fuel is injected during the intake stroke and main load of fuel is injected at an appropriate time in the compression cycle. Yet another mode is completely opposite of that. They also have multiple stage spark plug firing that varies along with those injection modes. They also figured-out how to keep the intake valves at the right temperature to prevent fouling, typical of DI engines.

Next comes the pistons... They are an advanced thermodynamic and structural design and are like nothing you've ever seen before. The cavity in the center is to kindle the combustion front and keep the forces centered. That, along with an engineered asymmetric weight balance minimizes skirt slap. The entire purpose of this is to have complete control of the detonation process.

The Skyactiv-G engines are absolutely tuned for performance and economy. The system adapts depending driver demand. The ASME (American Society of Mechanical Engineers) has been writing articles about Mazda engines for some time now. Some of the articles are publicly available. The Skyactiv-G platform is a predecessor to the Skyactiv-X engine which is a gasoline diesel engine (currently available in the Mazda3 in Germany).

Mazda's Skyactiv-G is optimized for economy and performance to the same extent an F1 engine is optimized for racing.

 

[spasm3]

Originally Posted by bbhero
Would you know how they managed to run a motor that is 13:1 compression on 87 effectively ??

ECM... Have a lot to do with that I am guessing... What else??

I am just curious how they could do that... And I think maybe you would have a good answer.



I thought that was the whole premise of direct injection. Higher compression ratios. Low octane and high compression in a non di engine results in pre-ignition. But if the fuel is not there it can't pre-ignite. Its injected just before top dead center and right before the combustion event.