Experience Running CX-90 Turbo S With US 87 Octane?

Has anyone been regularly running one of the Turbo S engines (nominal 340 HP) on US-standard regular unleaded (87 octane)?

I know there'll be a drop to 319 HP on the lower octane, and max torque caps at 3500 rpm vs. 4500 on premium, but have you experienced knocking or other things?

Given that Mazdausa does list the HP/torque for both premium and regular unleaded, it sounds like it should operate okay with it.
1708268331006.png
 
Last edited:
I expect it will work just as well as the 2.5T turbo. Mazda states both figures for that engine as well and it has been running fine on 87 for my CX-9 for the last 5 years. Not much changes on the 2.5T as long as you stay below 4000 rpm. Above 4000 rpm you really see the difference. It will likely be the same for the inline 6.
 
Agree with the above. Also if it behaves like the 2.5T, Coleman said in the winter you don't even need 91 to get the full hp, 87 should give you max. Summer is different though.
 
Always best to use 91 to prevent detonation on turbo cars. Remember, your computer will retard ignition timing when it detects detonation. Detonation comes first, computer adjustments second.

However, Mazda can't deny a warranty claim for using 87 octane if the owner's manual says you can, so I assume the computer is rather conservative.
 
Last edited:
Agree with the above. Also if it behaves like the 2.5T, Coleman said in the winter you don't even need 91 to get the full hp, 87 should give you max. Summer is different though.
I used to think this but I don't know that it applies to turbo cars. While cold temperatures help prevent detonation, it's not going to be enough to make the same power as 91 octane (let alone 93). The time to drop octane is at high altitudes and on long, steady, low-load road trips.

And there is another factor. Higher humidity reduces the need for octane. This means in the midwest USA when freezing temperatures brings very dry air, you may not see the engine needing less octane.
 
If this can put you at ease. I have not seen anyone on this forum with detonation damage to their engine.
 
Always best to use 91 to prevent detonation on turbo cars.
even if its non turbo. even if its not "designed" for 91 octane! in my experience, engine ran FAR smoother using 91, ethanol free, even though my skyactiv 2.5 says 87 only.
Remember, your computer will retard ignition timing when it detects detonation. Detonation comes first, computer adjustments second.

However, Mazda can't deny a warranty claim for using 87 octane if the owner's manual says you can, so I assume the computer is rather conservative.
ecu cannot differentiate between different octane types, only, which one burns with less knock/pre-detonation detected. I suggest sticking to 91.

switching to 91 paid itself off 100% . i calculated it. ran so much smoother too. I'm tuned for 91 octane now.
 
even if its non turbo. even if its not "designed" for 91 octane! in my experience, engine ran FAR smoother using 91, ethanol free, even though my skyactiv 2.5 says 87 only.

ecu cannot differentiate between different octane types, only, which one burns with less knock/pre-detonation detected. I suggest sticking to 91.

switching to 91 paid itself off 100% . i calculated it. ran so much smoother too. I'm tuned for 91 octane now.

Ethanol free is likely more what is affecting your experience than the octane level in engine not designed for 91.

Also some engine will see fuel efficiency gain with 91, some won’t. Saying that using 91 will pay itself off 100% is not true of all cars.
 
Where I live in NY it's a 25% premium for premium 91 vs. regular 87 unleaded ($4 vs. $3.20 right now, $5 vs. $4 when prices were higher). It would be a surprise if people are getting a 25% improvement in mileage on 91 compared to 87.
 
Ethanol free is likely more what is affecting your experience than the octane level in engine not designed for 91.

Also some engine will see fuel efficiency gain with 91, some won’t. Saying that using 91 will pay itself off 100% is not true of all cars.
Very true!
 
I do a lot of longer distance road trips and have tried 87, 91, and 93 with my regular 2.5L and have noticed no difference in fuel economy or performance depending on octane. What I do notice is cold temps are kind to the 2.5L when warmed up and you can get some low to mid 7s 0-60 times according to my OBD scanner (with 87 octane). You'd be better off going 5 MPH slower than going from 87 to higher octane fuel. I've gotten over 36 MPG going 55 MPH for 120 miles. I've also gotten 27 the same stretch going (allegedly) 75.
 
I do a lot of longer distance road trips and have tried 87, 91, and 93 with my regular 2.5L and have noticed no difference in fuel economy or performance depending on octane. What I do notice is cold temps are kind to the 2.5L when warmed up and you can get some low to mid 7s 0-60 times according to my OBD scanner (with 87 octane). You'd be better off going 5 MPH slower than going from 87 to higher octane fuel. I've gotten over 36 MPG going 55 MPH for 120 miles. I've also gotten 27 the same stretch going (allegedly) 75.
I've seen similar mpg and far lower with my Mazda 6 Skyactiv 2.5, from 36 - 47mpg at 100km/h, down to like 58mpg averaging about 50-60km/h steady. (Ethanol free)

As someone rightly pointed out above, going ethanol free can make a big difference.
 
Where I live in NY it's a 25% premium for premium 91 vs. regular 87 unleaded ($4 vs. $3.20 right now, $5 vs. $4 when prices were higher). It would be a surprise if people are getting a 25% improvement in mileage on 91 compared to 87.
That's almost half the price of fuel here in Canada.

There's a roughly 15% difference between 87 and 91 here. 10-15% difference in mpg after I made the switch
 
Still hoping to hear from any CX-90 Turbo S variant owners...

Love the continuing discussion, but if any CX-90 Turbo S owners can chime in with their experiences regarding engine knock while on 87 octane, that would be really helpful.

I wonder if new Turbo S owners are so few and so careful that they aren't really willing to test the waters with their own cars? Anyone leasing a Turbo S want to experiment a little? Lol
 
Maybe ask yourselves.
How often do you bring RPM above 4k?
If you do it frequently, maybe you should consider using 91.

I have been using 87 on my 2.5T ('22 CX-5).
Happy engine. Haven't observed anything abnormal.
It is not a sports car.
I don't bring it above 4K that often.
 
CX-9 here. I switch around and make sure I'm running premium when I plan on long highway trips. There's a noticeable difference at the top end. If you're pulling out to pass in heavy traffic at highway speeds, 87 Octane is not the fuel you want to be burning.
 
Last edited:
Still waiting to see if there are any CX-90 Turbo S owners who have tried regular 87 octane - this is a differently tuned turbo than the base Turbo, so comparisons with earlier turbo versions doesn't work.

Thanks for the inputs, though - it's always nice to hear how other Mazda engines perform.
 
CX-90 PHEV here....I switched to 93 as 91 is not available at the station I use 99% of the time. Performance is noticeable between 87 and 93. Much smoother experience when using the gas engine versus EV motoring.
 
Back