CX-9 2.5T drives better with 91 Octane

thugzy

Member
:
2016 Mazda CX9 Signature, 2013 Merc GLK350 4Matic, 2001 S2000
4200kms on my Signature and after experiencing 87, 91 vs 93 octane..... IMO, the engine has better drivability qualities using 91 Octane or higher.

At lower revs, I feel the engine is more responsive, has less turbo lag, and is smoother using 91 vs 87.... it feels very apparent when you are accelerating under full boost between 2000-4000rpms. Using 87 the engine's NVH is high.
At higher revs above 4500rpms, the power is noticeably higher while using 91.

For myself, I'm going to only use 91 based on what I have experienced.
 
I agree, for sure. A few tanks of 91, and it's noticeable. Mid range torque in 2nd and 3rd is really more usable. I am guessing Mazda limits HP in 1st, to keep things sane, and get you into 2nd quickly.
I'd be interested to see one of the tuners get a hold of the 2.5T, and see what its capable of. Not that I would upgrade, its my wife's car. :)
 
As for us, with 2 tanks of 93 and 2 tanks of 87 we have seen no difference in fuel economy. And having driven fairly consecutively we haven't noticed much difference in performance.
 
As for us, with 2 tanks of 93 and 2 tanks of 87 we have seen no difference in fuel economy. And having driven fairly consecutively we haven't noticed much difference in performance.


I have as well seen a negligible difference in fuel economy. I also agree, driving very conservatively you wont notice too much difference.... it all depends on driving style and environment.

My drive consists of 50/50 city/highway....there are many times where I need to accelerate more than conservatively (shifting 3-4000rpms) to pass or get around other motorists... Toronto drivers are ruthless!

However, if you drive steady highway at constant speed (not towing anything, or not needing to quickly pass people) you will be ok.... but this is not always the case
 
4200kms on my Signature and after experiencing 87, 91 vs 93 octane..... IMO, the engine has better drivability qualities using 91 Octane or higher.

At lower revs, I feel the engine is more responsive, has less turbo lag, and is smoother using 91 vs 87.... it feels very apparent when you are accelerating under full boost between 2000-4000rpms. Using 87 the engine's NVH is high.
At higher revs above 4500rpms, the power is noticeably higher while using 91.

For myself, I'm going to only use 91 based on what I have experienced.

Let me tell you I'm using Premium fuel as well. Feels better. No more regular gas on this beauty. My cx9 deserve it, the turbo love special gas. We don't have 93 in MX or 91, we have 92 octanes and damn I "feel" is now better.
 
we have seen no difference in fuel economy
Do you mine in miles per gallon, or in miles per dollar? The cost per mile is the true measure of economy.
 
I don't see a difference in miles per gallon, so the cost per mile was actually worse.

With that said, we just took a 450 mile round trip and averaged 26mpg. Most of the trip was interstate with adaptive cruise set at 72 mph and two moderate traffic jams, 20 mph headwind on the way down and negligible wind in the return journey. Pretty happy with that, our previous 2010 CX-9 FWD would have averaged 23 mpg.
 
Does anybody know what the horsepower number would be using 91 octane? I don't come across anything higher than that in most of the western US. Also wonder how the mid-grade 89 octane would be.
 
Does anybody know what the horsepower number would be using 91 octane? I don't come across anything higher than that in most of the western US. Also wonder how the mid-grade 89 octane would be.

Well, if it is a linear relationship between octane and HP, a 4 increase in octane should give ~15 hp increase, from 227 to ~242. This is just a guess because I really have no clue how the ECU deals with the octane levels.
 
Last edited:
Well, if it is a linear relationship between octane and HP, a 4 increase in octane should give ~15 hp increase, from 227 to ~242. This is just a guess because I really have not clue how the ECU deals with the octane levels.

I would also assume a linear relationship. Mazda probably stated HP figures based on the minimum (87) and maximum (93) octane range that is most commonly found at gas stations.
 
I would also assume a linear relationship. Mazda probably stated HP figures based on the minimum (87) and maximum (93) octane range that is most commonly found at gas stations.

If that is the case, 242 is not bad.

I will say, I recently did my first "highway" drive with the CX-9, about 200 miles and ended up getting 27 MPG. The speed limits were 55-65 mph and I generally drive at most 9 MPH above the speed limit. But I was happy to say the least. My old CX-5 would probably get 28-30 MPG in the same setting.
 
I don't see a difference in miles per gallon, so the cost per mile was actually worse.

With that said, we just took a 450 mile round trip and averaged 26mpg. Most of the trip was interstate with adaptive cruise set at 72 mph and two moderate traffic jams, 20 mph headwind on the way down and negligible wind in the return journey. Pretty happy with that, our previous 2010 CX-9 FWD would have averaged 23 mpg.

26mpg?

Jeez. In 20,000 miles, I've never broken 20mpg. 89 octane, 93 octane. Wide open highway, stop and go highway.
 
Really, how hard are you driving? I am getting close to 23 just driving around town.

I bought it for the zoom-zoom, right :)

In all honestly, not really any different than the Honda Pilot that I had before that - got right around 21mpg with that.

I do spend a LOT of time in stop and go traffic driving in the ring of hell around the Boston area. But even on clean highway trips in the low to mid 70's I've never seen anything approaching 26mpg.

I've long suspected, but have been unable to prove, that there is something off with my car.
 
I've long suspected, but have been unable to prove, that there is something off with my car.

Sounds like you are correct. i routinely get 22.4 mpg (10.5l/100km) just driving into town and back doing shopping and the like, and I averaged 26 mpg (9l/100km) on a recent highway trip of about 300 km, typically running at about 10 km/h over the limit. All on regular gas.

Could there perhaps be a problem with your right foot? :)
 
I bought it for the zoom-zoom, right :)

In all honestly, not really any different than the Honda Pilot that I had before that - got right around 21mpg with that.

I do spend a LOT of time in stop and go traffic driving in the ring of hell around the Boston area. But even on clean highway trips in the low to mid 70's I've never seen anything approaching 26mpg.

I've long suspected, but have been unable to prove, that there is something off with my car.

I wonder if the cold temps and bad traffic are playing a big role. I am now in South Carolina and a cold day for us is 45 degrees. Most days have been in the 50's and 60's since my purchase. That has to be close to ideal temps for a car! I am also pretty good about coasting when I can and I generally don't drive much over the speed limit in town and only up to 9 MPH over the speed limit on the highways
 
I bought it for the zoom-zoom, right :)

In all honestly, not really any different than the Honda Pilot that I had before that - got right around 21mpg with that.

I do spend a LOT of time in stop and go traffic driving in the ring of hell around the Boston area. But even on clean highway trips in the low to mid 70's I've never seen anything approaching 26mpg.

I've long suspected, but have been unable to prove, that there is something off with my car.


The likelyhood of something being wrong with a new car in that it affects fuel economy is super slim.
There's millions of variables that determine economy, mostly driving style. Engine development is extremely consistent with only rare lemons. My CX-9 also hangs around 20 mpg.
 
K
Well.. very cold weather will yield poor mpg

Very true indeed. I*ve been driving the turbo four in the 7 these past 12 years, and in extreme cold temps, say below 20 degrees F, gas miliage drops precipitously. If temps get into single digits, it is easily 20-25% fewer miles per gallon. That engine was never known for great efficiency, so a drop from 18 or 19, down to 13 or 14 mpg is very noticeable. I think turbos are likely more susceptible than naturally aspirated engines.
 
Back