Mazda 2.5 gasoline engine and high octane fuel

Let me preface this post by saying that I was a skeptic when people posted that the CX-5 performed "better" with high octane fuel when used in a non-modified engine.

So I sent a message to Mazda North America regarding the use of high octane fuel in the North American 2.5l 13:1 compression ratio engine.

Here is their response:

Thank you for contacting Mazda Customer Experience Center.

With regards to your inquiry, using a higher octane gasoline than what is recommended in the Owner's Manual offers no benefit as the SKYACTIV Engine has been tuned and calibrated to perform efficiently with 87 Octane Fuel (unless otherwise specified in the Owner's Manual). Using a higher octane fuel may only minimally improve performance or mileage.


I was surprised to see him add that last sentence, and now I'm thinking this is what some people were referring to. So it seems there is something, albeit minimal, there.

I have tried high octane fuel, and pure (no alcohol fuel) with no notable increase in power, or economy.

Goguinness said:

I have tried high octane fuel, and pure (no alcohol fuel) with no notable increase in power, or economy.

Click to expand...

And that seems to be in line with the response from Mazda.

I can't detect any change with 93 octane uncontaminated (no alcohol) gasoline.

I too tried high octane fuel and noticed nothing different. I concluded that it was a waist of money.

inlinev said:

So I sent a message to Mazda North America regarding the use of high octane fuel in the North American 2.5l 13:1 compression ratio engine.

Here is their response:

Thank you for contacting Mazda Customer Experience Center.

With regards to your inquiry, using a higher octane gasoline than what is recommended in the Owner's Manual offers no benefit as the SKYACTIV Engine has been tuned and calibrated to perform efficiently with 87 Octane Fuel (unless otherwise specified in the Owner's Manual). Using a higher octane fuel may only minimally improve performance or mileage.


I was surprised to see him add that last sentence, and now I'm thinking this is what some people were referring to. So it seems there is something, albeit minimal, there.

Click to expand...

Mazda engineers admit that 91+ octane will show some improvement BUT it depends on where and how you are driving. If you are riding around town on smooth and level surfaces keeping it under 4,000 RPM, then the difference will not be noticeable.

If you are taking on steep inclines, driving in mountain grades, towing or being fully loaded, driving in summer time with high outdoor temps, etc. Then the higher 91+ octane will make a difference.

Mazda engineers admit to it and when logging computers show the results, the SkyActiv engine pulls DRASTIC amount of timing a lot of time (reducing HP). If there is a slight hint of possible detonation (which happens more often than people think in these engines) the computer will pull timing and put the engine into "safe" mode and keep timing pulled for over 1 minute. The fact is the computer tables show drastic timing being pulled and the engine software puts the engine into a safe mode and it stays there for a long time, losing 10-40HP.

I read a post a few month back about this, so I tried it and I DID notice a difference. Been using 91 since.
It's nothing huge but it's enough to make me pay the extra $1.50 a fill up for it. I won't go back to anything less now.

Inclines are better, over-all revving is higher and more responsive to hitting the gas. And yes, RMP over 4K is when it kicks in.
Without it, the CX just kinda moves along in it's "MPG efficiency mode" and doesn't kick down as fast. It's a DOG on the climbs without it.

When tuned for it, it does wonders!! I'm tuned for 89 and can feel the difference big time!!

dragonsback79 said:

I read a post a few month back about this, so I tried it and I DID notice a difference. Been using 91 since.
It's nothing huge but it's enough to make me pay the extra $1.50 a fill up for it. I won't go back to anything less now.

Inclines are better, over-all revving is higher and more responsive to hitting the gas. And yes, RMP over 4K is when it kicks in.
Without it, the CX just kinda moves along in it's "MPG efficiency mode" and doesn't kick down as fast. It's a DOG on the climbs without it.

Click to expand...

"Doesn't kick down as fast"?

Are you suggesting that running 91 octane alters the transmission shift points? I have a hard time guessing how that could be.

It suggests that in normal driving it might get better mileage. Do you notice any difference?

Rarebit said:

"Doesn't kick down as fast"?

Are you suggesting that running 91 octane alters the transmission shift points? I have a hard time guessing how that could be.

It suggests that in normal driving it might get better mileage. Do you notice any difference?

Click to expand...

For me, going up long hills my car used to kick down two gears right away,,,, with higher octane the mapping makes more torque thus no need to downshift right away. And when it does, it's usually only one gear.
Plus, on hot days the timing cuts back way early,,,, with higher octane there is no need for the ECU to do so,,,, IE: More torque!

Is higher octane the perfect remedy for everyone? NO! We all have different driving situations, some may see a benefit, some may not.

I was so tempting to try 91, but decided to wait a little longer until I have a consistent feel for 87 to establish a baseline for comparison. However, 3,500 miles so far, and performance varies wildly. I found just a slightly different gas pedal position affects the throttle quite a lot, yet someday I sit a little straight, other days I lean a little back. Outside temp is also a huge factor, especially when the car just warmed up, I can totally tell if the engine is rough or smooth, and Minnesota weather at this time fluctuates between 50-80F.

It's also hard to consistently gauge the torque/power with just my butt. When going up a ramp, the impression of acceleration hugely depends on whether the car in front is a Prius or an Audi, whether the traffic is moving at 60mph or 80mph.

And then, I'm not patient enough to try to feel it any longer. Before I know it, my right hand just started moving the stick to M and shift up and down on its own. I was so thrilled with Sport mode at the beginning, but as I got used to manual shifting, I actually prefer controlling the gears myself (when needed) and found it's more than adequate to go uphill or keeping power ready for merging/passing.

I guess maybe I'll wait until I can feel the car better. Maybe after 10,000 miles, but I heard others mentioned that the car will feel different after the first oil change, that'd totally screw up the "baseline" I've been building up.

Thought it was nonsense until I tried the 91, picked up an extra 2 miles per gallon and has a little more oomph. Tried it on alternate fills. Had 2 months of warm dry weather around here lately. For me the extra cost doesn't warrant using it all the time whereas 89 is only 10 cents more and feels a tad better than the 87. Great discussion in this link also includes high octane use in the CX5 once you get past all the fighting..http://www.mazdas247.com/forum/showthread.php?123854217-CX-9-Skyactiv-2-5L-turbo-engine