Octane Rating

[watermelon]

Bumping this up, it's been nearly a month since anybody reported on using high octane in the North American spec 2.0L gasser.

Very interesting thread. Lots of thoughts 'n theory.

I can only speak to my experience. I come from a 2 wheel motor background and have developed a pretty good feel for the machine, so to speak.

When it came to my previous car, i ran back and forth between 87 (10% eth) and premium (0%). There were 2 things I noticed with premium - one was increased mileage. A significant amount? Not really, only about 30-40km more on average, but it was more.

The second was power delivery. Not in straight-up punching power but the engine response felt more lively, more sharp. It's a bit hard to explain. It's not a power boost. It felt as if the engine and acceleration was running right, just as it should, making power smoothly and cleanly. Crisp. With regular (10% ethanol), the engine always felt just a touch sluggish, like it wasn't firing properly when accelerating. It was definitely subtle, but it was there.

This doesn't surprise me though, ethanol has less chemical energy than dino oil.

Anyways, with my CX-5, I'm only on my 3rd tank of gas. The first two was 87 (10% E), this third one was with 94 (0% E). It's going to be awhile till i get used to the engine since i'm still in break-in, but I'll be very interested to see at least the mileage difference.

Either way, I'm going to be running 0% ethanol/premium in the CX5 for two reasons - one is to get away from ethanol (that crap is just filler). Two, I don't strictly trust that all the tricks the engineers came up with to deal with 87 in a high compression engine will work. Hot summer day, fully loaded with people and gear in the mountains.. i wonder if someone will experience some knock.

Anyways, the primary reason for premium is the lack of ethanol for me. Not having to worry at all about detonation will be a bonus. I'll report back on the mileage difference when this premium tank is done, hopefully will be an increase but prob not much

 

[sylva143]

Any updates from those experimenting with 87 vs 91/92/93 octane? I just filled up with Shell 93 octane today to experiment myself. I wan't so much thinking of fuel economy as engine preservation, as Shell advertises that its V-Power premium as 4 x the detergent of their regular and mid-grade. Now that I read this thread, it seems like there might be some modest boost in power with at 13:1 compression engine, so perhaps I'll see a benefit there. We'll see...

 

[CX-SV]

My guess is that owners trying this high octane experiment lose interest after finding no measurable impact on economy or power. They gradually tire of being just another sucker over-buying higher octane gasoline for no valid reason (some say it feels good or better, just like changing oil every 3000 miles).

btw - European version of the 2.0L gasser tuned for premium gasoline (and with higher 14:1 compression) gets about 8 more horsepower if I remember correctly. Done right that's the power increase.

 

[CXVille]

Everything else equal, higher octane will not, in a modern engine, get better gas mileage. If the engine is not tuned for it, it won't take advantage of it. If you want to test it yourself, go ahead, run a dozen tanks through and let us know. If you compare 10% ethanol to 0% ethanol, that is not apples to apples.

 

[MikeM.]

Any updates from those experimenting with 87 vs 91/92/93 octane?

I've been running regular since the car was new. But two fill-ups ago my receipt said I filled with Premium (and of course was charged the higher price). I thought I hit the regular button on the pump but, to err is human. In any case, the fuel economy from that tank was slightly below average. But one tank, even though driven in similar conditions, is not conclusive, especially considering the next fill-up was at another station and the point at which a pump shuts off will vary from station to station (and even from pump to pump). I would not expect to get better economy in a US spec. CX-5 simply by filling with premium.

But the case is not so clear with every modern car. My Volvo S80 (for example) is designed to run on any octane from 87-93. And it definitely feels smoother, makes more power and returns more range when run on premium. So that's what I use. But it dynamically "retunes" the engine mapping based upon feedback from the anti-knock sensor. All cars are not created equal. While the US spec CX-5 is not setup to take advantage of the higher octane fuels, it would not surprise me to learn that it will retune the engine mapping if it detects knock - for example, if the car was fueled with regular that only had an octane of 85 RON (which is actually available in some areas of the US). And, sometimes gasoline does not meet the minimum octane it is sold at. This is proven by periodic lab testing of gasoline supplies in various areas of the US.

I would be interested to learn if the US spec CX-5 has the capability to protect itself from fuel with octane below 87 RON by remapping the ECU.

 

[CX-SV]

Premium is recommended by Lexus for use in my IS for example, so I have used only Chevron premium. Given the 11.8:1 compression ratio (even w/port and direct injection), I really don't want to experiment with lower octane gasoline even if the engine is capable of adjusting to avoid damage with a negative impact on power and efficiency.

I do wish our US versions of CX-5 gas 2.0L and 2.5L were Euro-spec with the higher compression ratio, even if premium fuel was required. But I understand why Mazda spec'ed the US versions for regular given the market and the typical compact SUV buyers here.

 

[CXVille]

I've been running regular since the car was new. But two fill-ups ago my receipt said I filled with Premium (and of course was charged the higher price). I thought I hit the regular button on the pump but, to err is human. In any case, the fuel economy from that tank was slightly below average. But one tank, even though driven in similar conditions, is not conclusive, especially considering the next fill-up was at another station and the point at which a pump shuts off will vary from station to station (and even from pump to pump). I would not expect to get better economy in a US spec. CX-5 simply by filling with premium.

But the case is not so clear with every modern car. My Volvo S80 (for example) is designed to run on any octane from 87-93. And it definitely feels smoother, makes more power and returns more range when run on premium. So that's what I use. But it dynamically "retunes" the engine mapping based upon feedback from the anti-knock sensor. All cars are not created equal. While the US spec CX-5 is not setup to take advantage of the higher octane fuels, it would not surprise me to learn that it will retune the engine mapping if it detects knock - for example, if the car was fueled with regular that only had an octane of 85 RON (which is actually available in some areas of the US). And, sometimes gasoline does not meet the minimum octane it is sold at. This is proven by periodic lab testing of gasoline supplies in various areas of the US.

I would be interested to learn if the US spec CX-5 has the capability to protect itself from fuel with octane below 87 RON by remapping the ECU.

The ECU will have some latitude in this respect. From my experience, the ECU can retard the timing pretty far, but it will throw a CEL before it reaches it's limits. I'm not sure about the one in the CX-5 but expect it can handle 85 without to much trouble - from a safety standpoint.

 

[BRIAN_MP5T]

Do not go lower than what Mazda recommends. 85 is simply going to ruin the engine or throw timing so far that the underpowered engine will be even worse

 

[sylva143]

So, I'm a day into my experiment, which is of course too early to draw any conclusions. Fuel economy is inconclusive. One encouraging sign...I live on the side of a mountain with a very steep driveway. On the 87 octane, the car bogged down badly in second gear going uphill. My one experience last night with 93 was that the car zipped up the mountain in second gear much more easily. I'll try to replicate this over the next several days.

While I remain skeptical that the 93 premium will provide much benefit, I am a bit intrigued by the comments (posted here and on other forums) by the Mazda engineer who speculates that some modest boost in horsepower might be achieved with premium gas. The cost of a premium tank of gas is only $2.50 higher than the cheap stuff, so I don't feel too bad about doing some experimenting. The worst case scenario is that I run a couple tanks of V-Power through the system and enjoy the benefits that the extra detergents provide.

 

[CX-SV]

So, I'm a day into my experiment, which is of course too early to draw any conclusions. Fuel economy is inconclusive. One encouraging sign...I live on the side of a mountain with a very steep driveway. On the 87 octane, the car bogged down badly in second gear going uphill. My one experience last night with 93 was that the car zipped up the mountain in second gear much more easily. I'll try to replicate this over the next several days.

While I remain skeptical that the 93 premium will provide much benefit, I am a bit intrigued by the comments (posted here and on other forums) by the Mazda engineer who speculates that some modest boost in horsepower might be achieved with premium gas. The cost of a premium tank of gas is only $2.50 higher than the cheap stuff, so I don't feel too bad about doing some experimenting. The worst case scenario is that I run a couple tanks of V-Power through the system and enjoy the benefits that the extra detergents provide.

Been almost a week, other than perceptions of bogging, zip, and other signs, anything significant?

btw-The engineer speculating about modest boost in horsepower with premium gas has been silent now for over a year.

 

[IHeartGroceries]

I wouldn't speculate an output boost as much as I would improved linearity of the power band. I think, if any, the true benefits of running premium will come in the hot summer months, when the hotter intake temp/air charge will significantly increase the probability for knock on the very high compression engine, with the ECU implementing knock retard of the spark advance, in order to avoid pinging (and thus having a drop in power).

And as for Shells premium having more detergent, yes, it does. But you wont enjoy the full benefit of that, seeing as that detergent will never see an intake valve. I doubt also it will have much positive effect on injectors, seeing as DI injectors are so high pressure, gunking is a much less significant issue than on PI engines. May be a positive on keeping clean the tank pump and CDFP, however...

 

[sylva143]

Been almost a week, other than perceptions of bogging, zip, and other signs, anything significant?

btw-The engineer speculating about modest boost in horsepower with premium gas has been silent now for over a year.

Well, I'm away on vacation, so the test is temporarily on hold. Before leaving town, I burned approx 1.5 tankful s of 93 octane. Preliminary mileage seems as good or better, maybe an improvement of 1 mpg, but still in the margin of error. I will need some more time to see any additional trends. I've been averaging 31.5 mpg with 80 percent mountain highway driving.

As for power, there does seem to be some improvement in mountain driving. I do detect some better fluidity in acceleration within the same gear, and maybe some improvement in engine sound. I don't know if there would be much difference in flat-land driving, but my very early impressions of mountain performance are encouraging.

Will update late next week after I return.

 

[sylva143]

Now back from vacation, I feel like I can provide a bit better feedback on my experiement with Shell 93 octane fuel.

Let's start with fuel economy. While I am getting about 1.5 more mpg since starting the experiment, I must also report that the weather has warmed up nicely which also helps to improve gas mileage. I'm now getting 32 mpg versus about 30.5 mpg in mountain driving (80% highway) in my AWD model. Given the improving weather, I don't know that I can draw any firm conclusions.

We'll cover power next. Please don't expect an objective report from me. I don't have all the tools necessary for a scientific report, so I will report only on my impressions...Low end torque does seem a bit better -- just a perception of easier accereration in first and second. And for some reason, I do feel a bit more confident when merging at highway speeds, so perhaps there is some advantage at higher RPMs as well. I can't say that my experience has been transformed, but there does seem to be some modest improvement for me.

My last impression will be regarding engine noise, which I believe sounds slightly smoother and maybe not quite as buzzy as before. Again, this is a subjective evaluation

While I agree that the 2.0 CX-5 will run just fine on 87 octane, and that the engine is programmed to handle 87 without problems, it does seem logical to me that 13:1 engine might modestly benefit from better gas, once the computer recognizes a higher quality product and makes the necessary adjustments. I have determined, in my own subjective way, that there is some modest benefit. Since we really aren't talking about huge amounts of money, I'm completely happy with my decision to stick with 93, at least for a while.

 

[backpackerx]

For me it's an economical issue since mine runs great on 87. In my area there is a .40 cent spread between regular and premium. So taking those numbers above:

Regular = $3.55 30.5 mpg = 11.64 cents a mile
Premium = $3.95 32.0 mpg = 12.34 cents a mile

That .7 cents a mile higher would cost me $126 extra a year for Premium for the same equivalent miles. 18,000/yr in my case.

Another way of saying the same thing is for Premium to be worth it I would have to go from 30.5 mpg to 33.95 mpg.

I'm not saying don't do it, there could be other benefits from the higher octane and it's your car so I'm not one to tell people want to do with their own property. Just wanted to walk through my thought process when I considered higher octane so please don't read it the wrong way.

 

[dad of jon]

Premium is recommended by Lexus for use in my IS for example, so I have used only Chevron premium. Given the 11.8:1 compression ratio (even w/port and direct injection), I really don't want to experiment with lower octane gasoline even if the engine is capable of adjusting to avoid damage with a negative impact on power and efficiency.

I do wish our US versions of CX-5 gas 2.0L and 2.5L were Euro-spec with the higher compression ratio, even if premium fuel was required. But I understand why Mazda spec'ed the US versions for regular given the market and the typical compact SUV buyers here.

Minimum of 95 ron in europe, so europe gets 14:1 comp ratio and around 163hp compared to 155hp. about a 5% increase. I remember VW group having a 1.2 engine in standard and HC (high-compression) versions. If Mazda offered a HC version in the us then you'd have to commit to higher octane fuel for the ownership of the vehicle. I suppose only enthusiasts would go for that option, but then Mazda has more change of attracting that type of customer than some brands. perhaps they could offer it as a sport+ / sport-X with 6 speed manual.

 

[sylva143]

Ok, something new to report...

Now on my 4th tank of 93 octane, I am noticing that my MPG is going gradually higher. Before the experiment, I was averaging 30.5 mpg. I reset the computer when I filled with with 93 octane, and the average MPG has been steadily increasing, first to 31.5 mpg the second week, then to 32 last week, and now I'm sitting at 32.5. I realize that warmer weather can make a difference, but would a 2 mpg be realistic? I was skeptical about the MPG until now, as it is steadily increasing with idential driving.

 

[MikeM.]

I realize that warmer weather can make a difference, but would a 2 mpg be realistic? I was skeptical about the MPG until now, as it is steadily increasing with idential driving.

Yes, warmer weather can have quite a noticeable effect. The best way to check for this is to do three or four tanks of one, switch back to three or four tanks of the other and then do it all over again. If you chart your MPG on Fuelly (and there is a difference between the fuel blends in terms of efficiency) you will see a pattern emerge in the Fuelly graph. But I would not expect the higher octane to be advantageous unless the regular grade is not up to spec (either in terms of alcohol percentage, water in the gas or octane that is below specification). But that is just an educated guess. It is certainly possible there is something about the higher octane blend that makes it run more efficiently (and it probably isn't the higher octane rating).

When doing this type of testing/comparison, it is important not to have a personal bias that could make you drive faster or more aggressively with one blend than the other. It will also help to discern small differences in efficiency between blends if you wait until your tank is nearly empty before switching blends.

 

[jabba]

Ok, something new to report...

Now on my 4th tank of 93 octane, I am noticing that my MPG is going gradually higher. Before the experiment, I was averaging 30.5 mpg. I reset the computer when I filled with with 93 octane, and the average MPG has been steadily increasing, first to 31.5 mpg the second week, then to 32 last week, and now I'm sitting at 32.5. I realize that warmer weather can make a difference, but would a 2 mpg be realistic? I was skeptical about the MPG until now, as it is steadily increasing with idential driving.

And something else to take into account: ethanol in gasoline will yield lower mpg due to ethanol's lower energy content. So you should ensure that the ethanol content (if any) in the gas that you were buying is the same. I have heard that some companies may put more ethanol in their regular gas, but less in the premium.

 

[Gregx-5]

The warmer weather is having a noticable effect on my mpgs. It's easy to see especially since I drive the same road every day for work, holding to an exact speed on cruise control. I never hit 40mpg @ 60mph during the winter, but I've been doing it fairly consistantly.

The engine enjoys the warmer weather too. Past cars of mine seemed to prefer cooler air, like around 40 degrees, but this car runs differently (atkinson vs otto cycle), it's got to be related.

 

[CX-SV]

Note: Many living in major US urban areas will be impacted by change in gasoline from winter blends to summer blends, right about the time when weather is warmer. Impact on MPG will be noticeable.