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Thread: CX-9 2.5T drives better with 91 Octane

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    CX-9 2.5T drives better with 91 Octane

    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.

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    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. :-)

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    Quote Originally Posted by thugzy View Post
    I'm going to only use 91 based on what I have experienced.
    Have you measured the dependence of octane rating on fuel economy?

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    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.

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    Quote Originally Posted by dennyd75 View Post
    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

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    Quote Originally Posted by thugzy View Post
    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.

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    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.

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    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.

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    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.

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    Quote Originally Posted by Montanaman View Post
    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 by dougal; 02-11-2019 at 10:55 AM.
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    Quote Originally Posted by dougal View Post
    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.

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    Quote Originally Posted by sm1ke View Post
    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.
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    Quote Originally Posted by dennyd75 View Post
    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.

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    Quote Originally Posted by MattGoose View Post
    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.
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    Quote Originally Posted by dougal View Post
    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.

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