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Discussion Starter #1 (Edited)
UPDATE AS OF 169 POSTS IN THIS THREAD:
* It turns out the answer to the questions in the thread title are complex which can be elaborated on below, but the answer tot he shortest question od "Does it make a difference?" and the answer is "Yes."
* Throttle response is much improved at higher octane.
* Acceleration is better at half throttle or less because the ecu is actively advancing spark timing to the limits of knock, but at full throttle it doesn't make a difference, if anything it is hurting power because the fuel has less energy density and the ecu is not allowing the spark to be advanced.
* Fuel economy can be better on 87 and 91, but the evidence is 93 octane is probably a bridge too far, resulting in lower fuel economy.
Modified cars with an intake and or exhaust benefit more from the tune in every way, because it reduces the potential for knock since the aftermarket parts make the engine run more lean.
* The biggest variable of all for higher octanes helping or hurting is simply temperature. At temperatures above 90 degrees 91-93 octane is unarguably better than 87, and can make the difference between heavy knock changing the engine to safe mode operation and not. At temperatures between 70 and 90 degrees 89 offers many of the benefits of higher octane without much compromises. At temperatures below 70 degrees it seems 87 is adequate for best full throttle performance and fuel economy without hurting throttle response too much. So seasonality could help in choosing which octane is optimal for your needs.




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20 years ago the answer would have been absolutely not in stock form.

About 10 years ago it started to become a question worth asking though for the most part the answer was still "no":

http://www.caranddriver.com/features/regular-or-premium
“According to Gottfried Schiller, director of powertrain engineering at Bosch, these block-mounted sensors-one or two of them on most engines and about the size of a quarter-work like tiny seismometers that measure vibration patterns throughout the block to identify knock in any cylinder. Relying on these sensors, the engine controller can keep each cylinder's spark timing advanced right to the hairy edge of knock, providing peak efficiency on any fuel and preventing the damage that knock can do to an engine. But, noted Schiller, only a few vehicles calibrated for regular fuel can advance timing beyond their nominal ideal setting when burning premium…”

Keep in mind Bosch was one of the first movers in Direct Injection systems so they know what they are talking about.

Fast forwarding to today:

http://www.edmunds.com/mazda/cx-5/2014/long-term-road-test/2014-mazda-cx-5-octane-rating.html
I looked it up in the owner's manual. Of course, I found the familiar refrain:
[87(R+M/2) method] or above (91 RON or above)
What does it mean? It means you can put 87 or above in the tank. We're seeing this sort of "don't go below 87, but you can go above" language more and more. In fact, we even proved (here) that even if it isn't required, that running premium fuel can save you money, under the right circumstances and in the right car. "Your results may vary."

The Mazda6 Manual says the exact same thing as the CX-5 manual.

Also note the Chevy Cruze can take advantage of higher octane for improved fuel efficiency:
The Ultimate Hot Weather MPG Test - Regular vs. Premium - 2011 Chevrolet Cruze LTZ Long-Term Road Test
"We decided a deeper dive was in order, so we decided to subject the Cruze to an extended hot-weather MPG test. We sent the car out into Death Valley, where it spent an entire month sipping nothing but 87-octane regular, followed by another on the "good stuff", premium unleaded rated at 91 octane.
The results are surprising.
87 octane: 4,381 miles, 179.00 gallons
24.5 mpg
91 octane: 4,551 miles, 169.73 gallons
26.8 mpg"

After all, the more advance the spark the sooner ignition happens thus the longer the burn, the more efficient the use of fuel, thus better gas mileage.

As an example of an OEM explicitly stating that 87 is recommended but using Higher Octane helps is the following:

http://www.focusst.org/forum/focus-st-discussions/6010-regular-fuel-gas-petrol-87-89-octane-5.html
See attached image for Focus ST Owner’s manual Supplement.

In Europe the Mazda 6 runs on 91 and has a 14:1 compression ratio which gives 189hp and 189 lbs of torque, and I'd really like to see one run through the EPA test cycle to see what numbers it puts up. Should be substantially better than the US model.

So the real question is if the current Mazda 6 ECU is willing to advance spark timing right up against the knock sensor knock detection up through 91 or even 93 octane or is everything set up to stay away from knock with 87, and thus no benefits are possible?

Further, or is it set right up to knock detection at 87 such that when modifications such as a higher flow intake and exhaust are added that lean out the A/F mixture that knock does in fact start occuring forcing the ECU to retard the spark thus limiting the power and economy gains from those modifications?

Negatives of premium fuel is just to the wallet. Benefits are the potential gains above to fuel economy and power, but also the addative for the extra octane actually help keep the combustion chamber cleaner resulting in longer engine life.

I'm struggling to figure out any kind of testing methodology to prove that higher octane does or doesn't make a difference on our 6 if only because the changes would not be that dramatic in any case (perhaps a couple hp or extra MPG). Maybe dyno runs? or anybody with a very consistent commute trying both 87 and 91?

Thoughts?
 

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I've got some cash to burn, so I'll give it a shot. I track my mileage through Fuelly.com, and since adding the CorkSport exhaust and intake, I have not seen any changes in mpg's. I was thinking of trying higher octane fuel anyway to see what it would do. I drive the same amount pretty much every week, so I get pretty consistent mpg.
 

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I actually ran V-Power, 93 Octane on my last take and didn't see a noticeable difference in my fuel mileage over basic 87/89 octane. Just my experience.
 

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On my last Subaru I saw a difference between 87 and 93, but on two tanks of my M6, no difference.
 

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Once my exhaust is done I will do a baseline on 91. Then a few days later I may do another on 87. There may be some gains but if you look at my dyno runs, 3 runs within 3 minutes can have 1-2 percent difference in hp, which would probably be equal the small gains you might see. Therefore making it inconclusive. If I put in 87 and notice any difference I'll take it in for sure.


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[87(R+M/2) method] or above (91 RON or above)
Then this means that there is MOST LIKELY a power benefit from using higher octane. Owner's manual is written by engineers, this is legit
 

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higher octane helps when the engine is tuned for it by allowing more timing advance or higher compression. Where the UK engine is tuned for higher compression and premium is required, of course it helps. In the US, not so much, with a re-tune? maybe, but marginal gains at best even then.
 
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higher octane helps when the engine is tuned for it by allowing more timing advance or higher compression. Where the UK engine is tuned for higher compression and premium is required, of course it helps. In the US, not so much, with a re-tune? maybe, but marginal gains at best even then.
If an owner's manual, which is written by engineers says 87 or above, then 91 may produce some benefit
 
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Spent a month on 93 just to test it... Got .3 extra miles to the gallon.. Not worth it at all
what about engine sound/feel?
 

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I got about 10k on my 6 presently. I spent four full fuel tankfuls of 93 octane top tier gas searching for better mpg and hp.

Primarily I noticed a big dip in mpg's, about 1-2mpg loss going from 87 to 93. Very odd to me, as I expected the opposite. I've been tracking the mpg's manually with pen and paper since i purchased this car new for every fill up. Immediately switching back to 87 I got my 1-2mpgs back. From this reason alone I no longer use 93.

From a performance perspective, the engine runs a little better. The motor feels smoother and less laborous at full throttle right off idle.

My 2.5liter motor also pings noticably to my ears when flooring it, redlining up the gears. It seems to ping a little less with 93.

Under relaxed everyday driving, I notice no benefit, and only a slight loss in mpg. This is my wifes car, and she notices no difference.

Not worth the 50 cents per gallon difference to me. However if 87 vs 93 octane were very close in price, i'd stick with 93.
 

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Discussion Starter #14
@jon2002. This engine better not be pinging so new or it wont even make it to 60k. Sure you aren't hearing the injectors or something else?
 

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Discussion Starter #15 (Edited)
From the responses of those trying the higher octane (thanks for your inputs BTW) the initial verdict appears to be no benefit. Possibly it's even detrimental to engine performance and fuel economy (due to the lesser power density?) which is in conflict with what I've read elsewhere.

I might run 89 if I get an aftermarket intake to go with my custom exhaust because the engine will be running more lean than the engine was tuned for, and because it might keep things a little cleaner with all my short distance driving.

This is more fodder for a custom ECU tune that can take advantage of higher octanes for sure.
 

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It's probably not going to run more lean unless you really mod the engine or trick the ECU to think it is. This is common with intake systems but mainly from the trickery aspect since many are designed with less concern over what the MAF thinks about the situation. Modern ECU's are pretty clever at figuring out these issues, most OBD2 systems will even outsmart piggyback computers in all but open loop (mainly WOT) tuning.

Running higher octane really just controls detonation. Whether intentional (ignition timing) for power or engine degradation over time using it as a safeguard (less likely). If you were going on a road trip with four people and luggage through the mountains it wouldn't be a bad idea to help the engine with a bit of high octane. Same of you fill up at a less reputable gas station or end up taking the car to track days. Modern knock sensors are pretty amazing but better safe than sorry occasionally :).
 

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@jon2002. This engine better not be pinging so new or it wont even make it to 60k. Sure you aren't hearing the injectors or something else?

Unfortunately my 2.5l pings, i'm very certain it is. It's a rare occurance, only happens when the gas pedal is welded to the floor, and you are redlining the gears. I notice this the most at the top of 3rd gear, on the slowww climb to redline, about 5000-6000rpm. The pinging is quite transient, as in a split second here and there. I'm imagening the knock sensors are sensing it and pulling back the timing.

I've noticed this behavior anywhere from 15 to 100 degrees ambient tempurature.

I dont think 99.9% of Mazda6 owners will notice this. Fortunately this car is my wifes daily driver/baby hauler...she will never notice. The car is under powered for my preferance.
 

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Unfortunately my 2.5l pings, i'm very certain it is. It's a rare occurance, only happens when the gas pedal is welded to the floor, and you are redlining the gears. I notice this the most at the top of 3rd gear, on the slowww climb to redline, about 5000-6000rpm. The pinging is quite transient, as in a split second here and there. I'm imagening the knock sensors are sensing it and pulling back the timing.

I've noticed this behavior anywhere from 15 to 100 degrees ambient tempurature.

I dont think 99.9% of Mazda6 owners will notice this. Fortunately this car is my wifes daily driver/baby hauler...she will never notice. The car is under powered for my preferance.

Mine doesn't ping in those situations. Also even if the knock sensors are pulling timing to reduce the ping (pre-detonation) the damage is already done, and every instance adds to the problem, scarring the tops of the piston (and available portion of the cylinder walls) and degrading the spark plug every time. Beats some of the older MS3/6/CX7 engines with a few mods though... that audio voice yelling knock as they rip away full throttle without a care in the world.... those seem to hold up just fine too LOL. Mazda engines like ping? haha.

In all seriousness though, this engine is designed to get the heat inducing knock out, and ours in the US are even de-tuned to 13:1 on 87 vs 14:1 on 91. Something isn't working at 100% for there to be ping.
 

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Mine doesn't ping in those situations. Also even if the knock sensors are pulling timing to reduce the ping (pre-detonation) the damage is already done, and every instance adds to the problem, scarring the tops of the piston (and available portion of the cylinder walls) and degrading the spark plug every time. .
Mine doesnt ping, knock or hesitate either. I would think in 2014 with a 13:1 direct injected engine if it was suffering detonation at the least it would be throwing codes and maybe even the check engine light.

It's also possible there is some exhaust resonance that is mimicking pinging. Chassis are getting more and more quiet these days. Just a guess, no offense to the OP. :)
 

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Interesting others are not getting knocks from the same scenarios. I should definitely bring this to the attention of my dealer during its next visit.

Certainly not too thrilled about this.
 
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