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Mazda Skyactive octane/mpg #4228183
10/18/16 08:21 AM
10/18/16 08:21 AM
Joined: Jan 2010
Posts: 1,736
Rochester, NY
NateDN10 Offline OP
NateDN10  Offline OP
Joined: Jan 2010
Posts: 1,736
Rochester, NY
This summer I got a new car, a 2016 Mazda3, stickshift, 2.0L. In the US the owner's manual recommends 87 octane and the engine has a 13:1 compression ratio, but in other countries it recommends higher octane and has a 14:1 compression ratio. I was interested in whether higher octane would have any benefit in the US version of the engine.

I didn't do a super scientific test, just did 2 fillups of 87 octane followed by 2 of 93, then 2 more of 87 and 2 more of 93.
Here's the raw data:
Code:
fuelup_date	model	  miles	 gallons mpg	octane
10/17/2016	Mazda 3	  309.9	 8.295	 37.36	93
10/11/2016	Mazda 3	  306.6	 7.672	 39.96	93
9/22/2016	Mazda 3	  344.1	 7.846	 43.86	87
9/9/2016	Mazda 3	  334.6	 9.286	 36.03	87
8/29/2016	Mazda 3	  362.1	 7.806	 46.39	93
8/23/2016	Mazda 3	  362.7	 9.105	 39.84	93
7/28/2016	Mazda 3	  331.4	 9.206	 36	87
7/17/2016	Mazda 3	  302.7	 8.315	 36.4	87


And here are the statistics. I tried to do a box-and-whisker plot, but I can't spare the time to figure out how to make Excel give me what I want!
Code:
	87 octane mpg	93 octane mpg
median	36.215	        39.9
q1	36.0225	        39.22
min	36	        37.36
max	43.86	        46.39
q3	38.265	        41.5675


So it seems I get a little better mpg statistically with 93 octane, but it's certainly not worth the extra cost!


2016 Mazda3 - 20,000 mi.
2011 Toyota Sienna - 100,000 mi.
Re: Mazda Skyactive octane/mpg [Re: NateDN10] #4228196
10/18/16 08:36 AM
10/18/16 08:36 AM
Joined: Dec 2015
Posts: 571
Arkansas
mazdamonky Offline
mazdamonky  Offline
Joined: Dec 2015
Posts: 571
Arkansas
I think this has been discussed before on Mazda forums and tends to come to a similar conclusion. Though a lot of them decide to either run midgrade or 93 because they claim it seems to have a little better acceleration. In theory this makes since as it is a high compression engine and higher octane fuel would help substantially with keeping this engine from pinging which would let the engine run at full power more often.


2018 mazda3 hatch 2.5 263 miles
1985 rx7 1.1 98k miles
2002 protege 220k miles
1985 rx7 with a 5.0 swap
2002 Protege 299k miles Girlfriend's
4 more running cars in yard not mentioned
Re: Mazda Skyactive octane/mpg [Re: NateDN10] #4228204
10/18/16 08:47 AM
10/18/16 08:47 AM
Joined: May 2009
Posts: 12,189
N.H, U.S.A.
ARCOgraphite Offline
ARCOgraphite  Offline
Joined: May 2009
Posts: 12,189
N.H, U.S.A.
Its not all or nothing with octane. Its finding the sweet spot for optimum combustion timing. And sometime you might optimize a low rpm luggability to the detriment of high rpm. On my car with lowly 9.X comp ratio, it usually wants a couple to 3 gallons of 93 on top of the 87 tankfull in "dry" weather. In High humidity it does fine on swill.
Anymore octane and it gets sluggish. Also it appears to take more run time than you would expect to write over LT fuel trims and timing maps. I still am disappointed with typicall OBDII engine performance and mapping and snowballing/ detuning. Lambda control with safeguards aint what it could be. MAybe it is in UHP cars. I hear the monster corvette still has problems due to failsafe nannies where the engine choked at (possibly) bad fuel and would not build advertised boost/power. Think the was RodentRack?


2014 Nissan Rogue S CVT, OC#9 41392mi-QSUD10W30 + M110A CHAMP Filter; 2017 Subaru Crosstrek CVT OC#2 ?? mi-SOA/Idemitsu 0w20 + SOA Filter
Re: Mazda Skyactive octane/mpg [Re: NateDN10] #4228209
10/18/16 08:51 AM
10/18/16 08:51 AM
Joined: Dec 2008
Posts: 3,079
Occupied Virginia
Bottom_Feeder Offline
Bottom_Feeder  Offline
Joined: Dec 2008
Posts: 3,079
Occupied Virginia
Not sure where or why you're making a connection between octane and fuel economy. Higher octane is to fight pinging and pre-detonation, not for increasing fuel mileage although that may be the end result if the engine runs better on it (even if the manual says it doesn't 'require' it).

Running 87 octane in a 13:1 engine just does not seem right to me, but it's the 21st century so who knows.

Re: Mazda Skyactive octane/mpg [Re: Bottom_Feeder] #4228214
10/18/16 09:01 AM
10/18/16 09:01 AM
Joined: Jan 2010
Posts: 1,736
Rochester, NY
NateDN10 Offline OP
NateDN10  Offline OP
Joined: Jan 2010
Posts: 1,736
Rochester, NY
Originally Posted By: Bottom_Feeder
Not sure where or why you're making a connection between octane and fuel economy. Higher octane is to fight pinging and pre-detonation, not for increasing fuel mileage although that may be the end result if the engine runs better on it (even if the manual says it doesn't 'require' it).

Running 87 octane in a 13:1 engine just does not seem right to me, but it's the 21st century so who knows.

The idea is that the engine may have to retard timing to get pinging in check, and retarded timing reduces efficiency.


2016 Mazda3 - 20,000 mi.
2011 Toyota Sienna - 100,000 mi.
Re: Mazda Skyactive octane/mpg [Re: NateDN10] #4228241
10/18/16 09:29 AM
10/18/16 09:29 AM
Joined: Aug 2003
Posts: 12,896
NE,Ohio
Rand Online content
Rand  Online Content
Joined: Aug 2003
Posts: 12,896
NE,Ohio
The problem is gas mileage is dependent on conditions as well.

I always get better gas mileage in fall and spring.. or even with certain weather conditions.

Last night driving to Grove city I got [email protected] on the way there.

coming home I got [email protected]

Now If I had filled up @grove city would I say the gas did it?
but I didnt fill up it was merely atmospheric ie headwind.

Throw in A/C use traffic.. even stopping at a drivethrough.. and there is no direct comparison. In my Case it was a straight 90mile drive with no A/C use.

I do feel there might be a slight bump in MPG with 93 on my vehicle as well.. but its definitely not worth the 25% price difference for premium here
2.09 vs 2.59

Now If I had a turbo that is almost guaranteed to run better on 93 vs 87.



2019 Jeep Cherokee Trailhawk 2.0T
Re: Mazda Skyactive octane/mpg [Re: NateDN10] #4228242
10/18/16 09:33 AM
10/18/16 09:33 AM
Joined: Dec 2008
Posts: 3,079
Occupied Virginia
Bottom_Feeder Offline
Bottom_Feeder  Offline
Joined: Dec 2008
Posts: 3,079
Occupied Virginia
Originally Posted By: NateDN10
Originally Posted By: Bottom_Feeder
Not sure where or why you're making a connection between octane and fuel economy. Higher octane is to fight pinging and pre-detonation, not for increasing fuel mileage although that may be the end result if the engine runs better on it (even if the manual says it doesn't 'require' it).

Running 87 octane in a 13:1 engine just does not seem right to me, but it's the 21st century so who knows.

The idea is that the engine may have to retard timing to get pinging in check, and retarded timing reduces efficiency.

I get that, hence my '... if the engine runs better on it' statement.

Re: Mazda Skyactive octane/mpg [Re: NateDN10] #4228273
10/18/16 10:21 AM
10/18/16 10:21 AM
Joined: Apr 2008
Posts: 12,859
Onondaga County
Miller88 Offline
Miller88  Offline
Joined: Apr 2008
Posts: 12,859
Onondaga County
My parents GTDI Escape gets enough of a mileage increase going from 87 to 91 that the 91 ends up being something like $.50 cheaper per 1000 miles.

We calculated that a few years back when gas prices were higher and there was a larger price difference between 91 and 87. They went from 23 to 26/27 with it in daily commuting.


18 Forester 2.5I 6M
00 Jeep Cherokee
01 Ford F-350 XL 4x4 5M
Re: Mazda Skyactive octane/mpg [Re: Bottom_Feeder] #4228295
10/18/16 10:39 AM
10/18/16 10:39 AM
Joined: Sep 2016
Posts: 156
MN
Tman220 Offline
Tman220  Offline
Joined: Sep 2016
Posts: 156
MN
Originally Posted By: Bottom_Feeder
Originally Posted By: NateDN10
Originally Posted By: Bottom_Feeder
Not sure where or why you're making a connection between octane and fuel economy. Higher octane is to fight pinging and pre-detonation, not for increasing fuel mileage although that may be the end result if the engine runs better on it (even if the manual says it doesn't 'require' it).

Running 87 octane in a 13:1 engine just does not seem right to me, but it's the 21st century so who knows.

The idea is that the engine may have to retard timing to get pinging in check, and retarded timing reduces efficiency.

I get that, hence my '... if the engine runs better on it' statement.


So what is it you do not understand? or were you just making a statement?

I would say most cars these days with anything approaching 10:1 compression and above would benefit mileage-wise and power by increasing the octane.

This is due to the higher efficiency attained by keeping the timing advanced closer to peak efficiency rather than the point where the knock sensor gets angry. (as has been pointed out already) I have proven this with my own vehicles as well.

Last edited by Tman220; 10/18/16 10:41 AM.

2012 Regal GS Turbo PP 5w30
1994 Camaro Z28 LT1 355 CI, 430 RWHP PP 5W30
Re: Mazda Skyactive octane/mpg [Re: NateDN10] #4228310
10/18/16 11:04 AM
10/18/16 11:04 AM
Joined: Sep 2012
Posts: 5,381
DFW
DBMaster Offline
DBMaster  Offline
Joined: Sep 2012
Posts: 5,381
DFW
Too many uncontrolled variables involved in any fuel economy testing described on BITOG. Also, Mazda states 87 octane is to be used for Skyactiv engines in the U.S. That is why the U.S. version has lower compression than other countries' versions. If the car would "run better" or get better fuel economy on premium gas what would be the drawback of Mazda saying so in the owner's manual? I have seen no convincing evidence that using higher octane improves anything. I ran a few tanks of premium in mine and realized that if there was a difference I would need some sort of precision equipment to tell because I didn't "feel" anything.

Re: Mazda Skyactive octane/mpg [Re: Miller88] #4228317
10/18/16 11:08 AM
10/18/16 11:08 AM
Joined: Aug 2003
Posts: 12,896
NE,Ohio
Rand Online content
Rand  Online Content
Joined: Aug 2003
Posts: 12,896
NE,Ohio
Originally Posted By: Miller88
My parents GTDI Escape gets enough of a mileage increase going from 87 to 91 that the 91 ends up being something like $.50 cheaper per 1000 miles.

We calculated that a few years back when gas prices were higher and there was a larger price difference between 91 and 87. They went from 23 to 26/27 with it in daily commuting.


Right that is a turbo car. Almost always its worth it to run at least 91 octane in those.

the FA20DIT in some subaru foresters has a 10.6:1 ratio and boost(psi) in the mid-high teens. giving it a very high effective compression ratio. .. it will run "crippled" on 87 but 91+ is really a must.

The FB25 NA has a 10:1 and I can tell with 93 some difference over 87 however my gas mileage would have to go up near 7mpg to cover the cost difference so unless I know I'll be towing in hilly terrain I usually roll 87 octane.

Now back when it was 10cents extra for 89 and another 10cents for 93 (20c total)
I would just run 93 because I hate pinging.

Right now the premium is more 50-60C total for 93 vs 87. or around 25%


2019 Jeep Cherokee Trailhawk 2.0T
Re: Mazda Skyactive octane/mpg [Re: NateDN10] #4228332
10/18/16 11:32 AM
10/18/16 11:32 AM
Joined: Mar 2010
Posts: 1,001
SE Wisconsin
danthaman1980 Offline
danthaman1980  Offline
Joined: Mar 2010
Posts: 1,001
SE Wisconsin
In my '14 Mazda 6, I get better mileage on premium too.

The high-compression Skyactiv engines pull all sorts of tricks in order to avoid predetonation with lower octane gasoline. One particular trick I heard somewhere is that when you use regular gas, the engine runs slightly rich (maybe only under load) to keep the pistons cooler. Not sure if this is accurate, but given that it has been widely reported that Skyactiv engines have avoided fuel dilution by using premium gasoline, it stands to reason that the reason for the fuel dilution could be that the engine is running rich on 87.


2003 Chevy Silverado 1500 5.3 LS Quadrasteer ~230,000 miles; M1 0W-30

2014 Mazda6 Sport 2.5 Skyactiv ~40,000 miles; M1 AFE 0W-20
Re: Mazda Skyactive octane/mpg [Re: NateDN10] #4228346
10/18/16 11:53 AM
10/18/16 11:53 AM
Joined: Dec 2010
Posts: 436
Indianapolis, IN
09_GXP Offline
09_GXP  Offline
Joined: Dec 2010
Posts: 436
Indianapolis, IN
Here's a boxplot and 2 sample t-test showing that the MPGs with 87 is not statistically less than the MPGs with 93.


image upload

upload foto


2017 Miata Global Cup Car #02 - Castol A3/B4 5w30 w/ OEM Fitler
2017 Miata RF - PP 0w20 w/ M1 Filter
2015 F-150 2.7L Ecoboost - PPPP 5w30 w/ MC
Re: Mazda Skyactive octane/mpg [Re: danthaman1980] #4228365
10/18/16 12:26 PM
10/18/16 12:26 PM
Joined: Sep 2012
Posts: 5,381
DFW
DBMaster Offline
DBMaster  Offline
Joined: Sep 2012
Posts: 5,381
DFW
Originally Posted By: danthaman1980
...it has been widely reported that Skyactiv engines have avoided fuel dilution by using premium gasoline, it stands to reason that the reason for the fuel dilution could be that the engine is running rich on 87.


I have seen it reported by one member on BITOG. Do you have other references to this phenomenon other than badtlc's posts? I ran 30,000 miles on the same oil using microGreen filters and had no signs or symptoms of fuel dilution in the UOA.

Re: Mazda Skyactive octane/mpg [Re: 09_GXP] #4228379
10/18/16 12:41 PM
10/18/16 12:41 PM
Joined: Jan 2010
Posts: 1,736
Rochester, NY
NateDN10 Offline OP
NateDN10  Offline OP
Joined: Jan 2010
Posts: 1,736
Rochester, NY
Originally Posted By: 09_GXP
Here's a boxplot and 2 sample t-test showing that the MPGs with 87 is not statistically less than the MPGs with 93.


image upload

upload foto

Thanks!


2016 Mazda3 - 20,000 mi.
2011 Toyota Sienna - 100,000 mi.
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