Octane Rating

Hi!

I purchased my 2013 CX-5 back in beginning of May. After the initial tank of gas that the dealer filled for me, I have been putting in two tanks of 91 from Chevron. But the last fill up i decided to put in 94. I know the manual says put in 87 octane and up with no more than 10% ethanol. At local gas stations in BC, Canada, only 94 is ethanol free. I thought because of the high compression of the skyactiv-g would perhaps benefit from the 94. Since putting in 91 and 94, I have noticed the exhaust note seems to have more of a "growl" to it compared to the 87 that the dealer put in. Just wondering have other people tried it as well or just the "mind trick" that my mind is playing with me(wow)

Thanks!

It has to do with what the engine was designed to run.

High Compression or not.. if the timing curve of the car was not designed to operate with 93 or 94, the you could actally make less HP and look silly doing it because the fuel is $0.10 - $0.15 more / L


I believe that you are wasting your money. Run 87

Just 87 for me. That's what the engine was designed to run with, so that's what I use.

Thanks for the input! What about the ethanol part? I have read ethanol is undesirable for engines...

Agreed "mind trick".

actually they had to lower compression in usa to 13:1 due to the lower octane. performance MAY be better with higher octane because most PCMs nowadays advance timing until detonation is detected then back it up so higher octane would allow for more timing

neit_jnf said:

actually they had to lower compression in usa to 13:1 due to the lower octane. performance MAY be better with higher octane because most PCMs nowadays advance timing until detonation is detected then back it up so higher octane would allow for more timing

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Actually Mazda selected the 13:1 ratio for US market so that regular fuel could be specificed (they didn't have to, they chose to), so main impact of running higher octane premium fuel will be felt in wallet, not noticeably increased horsepower.

In Europe Mazda uses a 14: ratio and specifies a higher octane premium fuel requirement, and horsepower is reported as higher too.

neit_jnf said:

actually they had to lower compression in usa to 13:1 due to the lower octane. performance MAY be better with higher octane because most PCMs nowadays advance timing until detonation is detected then back it up so higher octane would allow for more timing

Click to expand...

Yea I wonder too if the PCM would advance timing enough to have a benefit.

kampfire said:

Yea I wonder too if the PCM would advance timing enough to have a benefit.

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A tank of premium to try/experiment would not hurt.

I'm in the camp that running 91 octane will improve performance and mileage. I disagree with CX-SV here, SkyActiv-G is great, but it doesn't prevent knock.

Our USA CX-5's run 13:1 instead of 14:1 so we are able to run 87. That doesn't mean that they don't knock running 87 octane, or prefer running crappy gas. The engine knock is more simply more tolerable at 13:1 and won't damage the engine. Mazda intended the original SkyActiv-G engine to run on premium fuel. We can't be trusted over here to run 91 all the time, so we get a lower performance Skyactiv-G.

I'm currently running 3/4 of a tank of 91 octane, mixed with 87. I've noticed that low end response has improved slightly. I can also report MPG avg on the dash is now showing around 32 instead of 28. If the on board computer's range is correct I should get about 415 miles out of this fill up. I'm at 260 miles on this fill up and have 1 dot less than 1/2 a tank to go. I'll post my final results, but with MPG this good it may be a while. I'm interested to see if a full tank of 91 will improve it much from what it is now. I'm doubtful there will be much more improvement. I've also got less that 600 miles total, so I'm still in the break in period. My car is a manual transmission, but I would think the automatics would see at least some gains in MPG. For me, I think that running 91 may actually cost less per mile than running 87... YMMV

We have a road trip coming up in the next couple weeks. Im going to try a tank back to back and see.

That sounds totally Scientific..



Ambient Temp Uncontrolled.
Barometric Pressure Uncontrolled
Driving Style Uncontrolled

I know I am coming off as a troll..

Bad data is better than No Data. Sometimes..

I drive about 50 miles a day and get about 35mpg on the dash. I'll run this tank of 87 dry and run 91 and report back. Got a full tank now though so it will be a few weeks.

I've seen many experiments done regarding higher octane fuels and their impact on performance and fuel economy. I tried to find a couple of them because they are a perfect illustration of everything discussed here.

Firstly a quick explanation of the Octane rating variances to avoid confusion.

There are two international measures of Octane:
Research Octane Number (RON) - A fuel is measured in laboratory conditions using a control engine throughout many compression-ratios then comparing to the standard output of two control alcohols.
Motor Octane Number (MON) - Uses a similar method to above but is a test of fuel under high load conditions. The ignition timing is changed, fuel is pre-heated and the engines rpm is much higher. This measure is typically used for aviation and is used to test racing engines.

Out of the two, RON is used internationally to measure the octane level of cars mainly because MON is a pointless figure for road legal vehicles.

The US (and therefore coincidently Canada) have adopted an altered Octane measurement; a fence sit between RON and MON.
The measure used is called AKI (Anti-Knock Index/Rating) is used, which is roughly an average of RON and MON.
On some pumps you may see this noted as R+M/2 (Or RON + MON / 2)

In the videos therefore, the typical Octane ratings quoted are 91 RON, 95 RON and 98 RON - which are in US Terms, 87 AKI, 89 AKI and about 91.5 AKI respectively.

Will power and torque improve?
The summary in this video is that it really depends on the vehicle and what fuel it is designed for.
A side note is that the Golf GTI when sold in Australia as a 98 RON only vehicle whereas in the UK it's 95 RON optional 98 RON.
Conversely the CX-5 is sold as a 91 RON in Australia (13:1 compression) just like US, whereas the UK gets the 14:1 95 RON version.

I have seen tests done on a 91 tuned vehicle which was drained of fuel the multiple tests on the 91, 95 and 98 fuels to show that the 98 did in fact allow greater fuel economy that the lesser octane fuel. But choosing one over the other really depends on the cost of the local fuel versus the actual % of distance gained.
If for example you gain an addition 4% range, but it costs 5% extra then it's not worth it.

But it is worth testing.
With my previous Mazda 3 I noticed fueleconomy benefits that were roughly similar to the additional price. So I decided to stick with 98.

In Australia of late as well, 91 is sometimes E10, whereas 95 and 98 are not allowed to contain ethanol by law. Anything greater than E10 is banned by law (flex-fuel cars are not sold in Australia).

MPG has to have the cost of the fuel included in the calculation.

If I am getting 100 MPG running on a fuel that is $75.00 Per Gal then it isn't a good value..

BRIAN_MP5T said:

MPG has to have the cost of the fuel included in the calculation.

If I am getting 100 MPG running on a fuel that is $75.00 Per Gal then it isn't a good value..

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Of course cost is what really matters, but added performance is also a nice benefit too. I put together an Excel spreadsheet to help with my "miles per dollar" calculations. At current gas prices, the extra 20 cents per gallon is worth it if I'm able to get only 1.4 MPG better running 91. Everything so far points to a least 2 MPG better, maybe up to 3 or 4 at the very most. I plan on running at least 2 more full tanks of 91 to get a better average MPG estimate. I'm not sure I'll want to swtich back to 87, so maybe someone else with a FWD 6MT can provide so additional numbers. I signed up for a Fuelly account so I can track and share data.

I will be experimenting with this as well. Just reached 2000 miles on the odometer running only 87, filling up at 1/8 of a tank. When Im empty Ill be using 91 for hopefully about the same miles. Tracking on fuelly too.

Interesting thread.....what kind of mileage do you think we would get running 104+ Octane fuel(thought)

^ 104+, like wow for even a bigger "mind trick". Already we have speculation about getting 2, 3, maybe 4 more MPG.

I just came across this thread while my last fuel up was with 91 for the first time, I do believe my cx-5 has a little more pep than on 87... I also noticed what looks like better MPG, but again, different day, different driving, etc.

I think I may go for 3 tanks and report back when I put some 87 back in there. I think the best test would be to have someone else fill the thing for me and not tell me when 87 or 91 is in there.