Octane?

very simple... just like any other engine/car out there, the ECU's strategy to avoid/prevent/stop detonation under the right conditions (hot weather, high engine load), is to run the engine richer (increase injector duty cycle, reduce ignition timing)... since the SkyActiv is known to run in full closed loop ECU operation (knock sensor is utilized at all times), running high octane gas WILL allow the fuel mixture to be leaner, thus excess unburned fuel will not get "washed down" past the piston rings into the oil pan

oil analysis reports can be found on other forums that proves this




This guy used 87 octane, had 0.5% fuel on a 5,300mile interval. A non-issue, even addressed in the UOA from the lab.
https://bobistheoilguy.com/forums/ubbthreads.php/topics/4056275/Mazda_0W-20_moly_-_5,370_miles

This guy with a 2.0, DID notice that running higher octane reduced fuel %:
https://bobistheoilguy.com/forums/ubbthreads.php/topics/3536768/High_Fuel__2013_Mazda_CX-5_2.0

This guy has no problems (no octane listed):
https://bobistheoilguy.com/forums/u...16/2016_Mazda_CX5_2.0_7,898/12,97#Post4197416

This guy uses 87 octane. No issues:
https://bobistheoilguy.com/forums/u...50/2016_CX-5_Sport_2.0_6MT_5,073/#Post4178550

Nearly 9K miles on this UOA, no issues really, but there is discussion:
https://bobistheoilguy.com/forums/u...86/Mag1_Ow20_-_8,951_Miles_-_'16.#Post4167486




Long story short: If you change oil at 5K miles, who cares? If you like to do the 10K mile thing, yeah, you may want to consider running premium.
 
very simple... just like any other engine/car out there, the ECU's strategy to avoid/prevent/stop detonation under the right conditions (hot weather, high engine load), is to run the engine richer (increase injector duty cycle, reduce ignition timing)... since the SkyActiv is known to run in full closed loop ECU operation (knock sensor is utilized at all times), running high octane gas WILL allow the fuel mixture to be leaner, thus excess unburned fuel will not get "washed down" past the piston rings into the oil pan

oil analysis reports can be found on other forums that proves this

That sounds reasonable. Thanks for the info.
 
Thanks for finding this AAA Premium Fuel Research report. I guess this conclusion from the report should summarize it all:



My biggest question is why the "real-world" horsepower is only about 80% of the rated horsepower on paper? The 3 test-runs for maximum horsepower on Mazda3 Grand Touring 2.0L I-4 which has horsepower rating at 155 @ 6000 rpm are 126.28/126.79/126.54 hp with 87-octane regular fuel and 129.78/129.25/129.52 hp with 93-octane premium fuel. This happens on all 3 test vehicles, a Tundra 5.7L V-8、a Charger SXT 3.6L V-6、and a Mazda3 Grand Touring 2.0L I-4. Why the discrepancy is so huge? (uhm)

So mazdadude, you won't get 188 hp with your 91-octane premium in reality, you can only get 152 hp at most from your 2.5L! (boom08)


The difference in horsepower ratings comes from measuring it at the crankshaft vs at the wheels.
 
Last edited:
Ok, as Mike said, the ECU is the boss. The O sensors and knock sensors are always on. The ECU's strategy is to always push the motor to the edge of knock then retard as needed.
Meaning, you will always have the slightest degree of knock. Most people, like unobtainium, will never see an improvement from higher octane. Some other people, like myself clearly see an improvement as the ecu has a set limit that it advances timing under certain conditions.
Those of us with tunes (Chris Top Her & myself) have those limits raised therefore taking advantage of higher octane. And it's very clear to us that the engine responds very well to the higher octane!
Those that notice very little or nothing with higher octane don't operate their vehicles (at least most of the time) where timing pull is greater than normal and/or just don't feel the 3-4 HP gain. (nobody feels 3 hp!)

Only true way to tell is to put in a OBD reader and datalog full timing and timing pull. Those with regular 87 octane may only have 20* total timing with only a degree or two of pull normal driving, those that use their cars heavily loaded, hot temps, high altitude may notice 4-5* pull and less power, using mid grade fuel they may have only 1* timing pull and slightly better feel while driving.
Those of us that are tuned for higher octane (I have a tune for 89 and 93 octane) will have say a max of 25 or even higher max timing limit and can really feel the difference,,,, especially on the top end as I do!

So yes, it is very viable that some people notice nothing while others do running higher octane on a standard tune, and not everyone's results will be the same.
Therefore unobtainium is correct in that he notices nothing and others are correct when they say they do. It all depends on your conditions and weather/ vehicle load.

Disclaimer: the numbers I used for total timing were pulled out of the air,,,, I have no idea what Mazda or OV uses for total timing.

Sadly, these octane threads always turn into slight bickering when in fact everyone replying is mostly correct in what is said, regarding their own results. Only thing I can say is try it for yourself! you don't need 93 octane,,, unless your tuned for it, but running a tank of 89 when driving in hot and fully loaded conditions to feel for yourself how it drives is your best bet,,, when backed up by an identical run on regular 87 fuel.
 
Last edited:
I run 93 octane during the summer. I'm running 87 octane now because it's colder. While I don't have hard scientific data, I feel like there is a little bit better response while on 93. I also seem to get slightly better MPGs while running 93 octane fuel.
 
Thanks for finding this AAA Premium Fuel Research report. I guess this conclusion from the report should summarize it all:



My biggest question is why the "real-world" horsepower is only about 80% of the rated horsepower on paper? The 3 test-runs for maximum horsepower on Mazda3 Grand Touring 2.0L I-4 which has horsepower rating at 155 @ 6000 rpm are 126.28/126.79/126.54 hp with 87-octane regular fuel and 129.78/129.25/129.52 hp with 93-octane premium fuel. This happens on all 3 test vehicles, a Tundra 5.7L V-8、a Charger SXT 3.6L V-6、and a Mazda3 Grand Touring 2.0L I-4. Why the discrepancy is so huge? (uhm)

So mazdadude, you won't get 188 hp with your 91-octane premium in reality, you can only get 152 hp at most from your 2.5L! (boom08)

126bhp? Really? That's about what an automatic 2002 Infiniti G20 I4 2.0L (I had one) dynoed. Mazda needs to step up. It's not 2002 anymore!
 
The safe buffer is already present. It's called your ECU.

This is craziness. Just buy 87 unless you are competing with someone in a dyno-test war.

A good 1 1/2 years later........

Okay I've been using 89 octane for well over a year. So I needed gas bad but nearest station only had 87 octane. Shell. Filled up. Man 87 octane felt zippier. For us spec CX-5's MAzda3's and Mazda6's....NA models....just use 87. Don't go against the grain on the ECU tuning.

Miata's and turbo models use 90+
 
I think it's likely more important long term to get good quality gas from a reputable supplier (injectors, deposits etc).

Up here in Canada I find PetroCan gas is awful personally. Chevron and Esso are good, Shell 'ok'. Otherwise, just put the gas octane in your manual calls for.
 
The AAA report quoted earlier in this thread showed the Mazda SkyActiv high-compression engine gained 20HP at the crank with the high octane.

I only use 91+ in the summer and when towing. When I ran 87 octane in the summer, towing a trailer, climbing a grade, the engine would pull some wicked timing and the CX5 would not fair well. Once I ran the 91+ mix, it didn't pull the timing like it did with the 87 octane.
 
The AAA report quoted earlier in this thread showed the Mazda SkyActiv high-compression engine gained 20HP at the crank with the high octane.

I only use 91+ in the summer and when towing. When I ran 87 octane in the summer, towing a trailer, climbing a grade, the engine would pull some wicked timing and the CX5 would not fair well. Once I ran the 91+ mix, it didn't pull the timing like it did with the 87 octane.

On a hot day, totally possible. I know LS1 cars heat-soaked bad at the track, for a drag-racing datapoint. That said, why bother? It's for economy, not for speed, so get your economy, unless you're taking it to Import Tuner Night on a hot, muggy Saturday night.
 
On a hot day, totally possible. I know LS1 cars heat-soaked bad at the track, for a drag-racing datapoint. That said, why bother? It's for economy, not for speed, so get your economy, unless you're taking it to Import Tuner Night on a hot, muggy Saturday night.

If I am pulling a trailer, up a grade, in the summer, I would rather pay the extra few bucks for 91+ octane than deal with timing being pulled and the vehicle falling flat on its face.

10 gallons of 91+ is only $3.00 more vs 87 octane. Worth it for me when the above is at play.
 
If I am pulling a trailer, up a grade, in the summer, I would rather pay the extra few bucks for 91+ octane than deal with timing being pulled and the vehicle falling flat on its face.

10 gallons of 91+ is only $3.00 more vs 87 octane. Worth it for me when the above is at play.

Sure, I get that, but I mean as a daily matter of course.
 
Does high octane really affects SkyActiv engines?

AFAIK the difference between 87 and 91 octane is that the 91 has a higher tolerance for compression ignition. Other than that, I don't know of any.
 
Does high octane really affects SkyActiv engines?

AFAIK the difference between 87 and 91 octane is that the 91 has a higher tolerance for compression ignition. Other than that, I don't know of any.
Depending on your driving situation. In harsh condition such as Lbear mentioned above, higher octane gas definitely will help high-compression SkyActiv-G engines performing better! TheMAN said it the best:

very simple... just like any other engine/car out there, the ECU's strategy to avoid/prevent/stop detonation under the right conditions (hot weather, high engine load), is to run the engine richer (increase injector duty cycle, reduce ignition timing)... since the SkyActiv is known to run in full closed loop ECU operation (knock sensor is utilized at all times), running high octane gas WILL allow the fuel mixture to be leaner, thus excess unburned fuel will not get "washed down" past the piston rings into the oil pan

oil analysis reports can be found on other forums that proves this
 
Depending on your driving situation. In harsh condition such as Lbear mentioned above, higher octane gas definitely will help high-compression SkyActiv-G engines performing better! TheMAN said it the best:
Thanks. Based on his post, he said for SkyActiv engines, it will run leaner. Meaning less fuel.
 
I didn't realize you had the Sentra gt..sorry

Aside from maintenance issues, it was actually a pretty neat little vehicle. I used it as a daily when my fun car was a C6 Z06. It got 31mpg on long road-trips doing 80mph, and it had more technology and features than my 2015 CX5 Touring.
 
Last year, when we were on summer vacation, I was driving from eastern Tennessee through western N Carolina and I filled up on premium gas because I remembered this thread and I knew that we would be heading into the Appalachian mountains. I had the Mazda loaded up (Wifey, beach chairs, tent, cooler, luggage, ETC). It seemed to me that the car drove well through the mountains. I think that the premium helps and will run premium again when I drive through that area again. Could this be the placebo effect? Perhaps, but it seemed real enough to me that I will pay the extra for high test gas next time I'm there.
 
Last year, when we were on summer vacation, I was driving from eastern Tennessee through western N Carolina and I filled up on premium gas because I remembered this thread and I knew that we would be heading into the Appalachian mountains. I had the Mazda loaded up (Wifey, beach chairs, tent, cooler, luggage, ETC). It seemed to me that the car drove well through the mountains. I think that the premium helps and will run premium again when I drive through that area again. Could this be the placebo effect? Perhaps, but it seemed real enough to me that I will pay the extra for high test gas next time I'm there.

Like I said I've been running 89 for a whole 1 1/2 years. Went to 87 and felt a noticeable zippy difference. I'll try another tank of 87 from a different station this time.

If it is the placebo affect then hey I like it :)
 
The AAA report quoted earlier in this thread showed the Mazda SkyActiv high-compression engine gained 20HP at the crank with the high octane.

I only use 91+ in the summer and when towing. When I ran 87 octane in the summer, towing a trailer, climbing a grade, the engine would pull some wicked timing and the CX5 would not fair well. Once I ran the 91+ mix, it didn't pull the timing like it did with the 87 octane.

you might want to read that study again. The gain was 2HP! not 20!
 
Back