Premium gas

chckboy5 said:

Do you guys have a preference on which top tier gas to use?

Click to expand...

It doesn't really matter. While there are measurable differences between different batches of fuel (depending upon which refinery unit it came from, when it was made, even the weather), fuel is treated like a commodity so the same fuel gets delivered to multiple locations with different branding. There are different additive packages for branded fuel but any top tier fuel will have adequate additives.

I buy fuel from the top-tier stations that have the lowest prices and return the highest MPG. If I notice a batch of fuel is not working as well I'll try another station next time. Works for me.

chckboy5 said:

Do you guys have a preference on which top tier gas to use?

Click to expand...

Given a choice, go with ethanol free if you can find it. (more BTU and less damaging to engine parts)

davefr said:

Given a choice, go with ethanol free if you can find it. (more BTU and less damaging to engine parts)

Click to expand...

That 10% ethanol will damage engine parts is an old wives tale created when fuel systems had rubber/plastic parts that were not alcohol resistant.

All late model cars are DESIGNED to be run on gasoline with 10% alcohol!

No damage will occur. None.

inlinev said:

Where do you see this? The sky active engine was specifically designed to work with 87 octane.

Click to expand...

If you go to the SAE site where the engines are tested and achieve official numbers. They used 91 octane to get their peak HP/Torque #'s

Yes, Mazda SkyActiv was designed to work with 87 octane BUT it does NOT achieve max/peak HP with 87 octane. If it's 95F outside and you have 4 people in the vehicle and climbing a hill. I guarantee you the computer is de-tuning the engine to prevent knock with 87 octane. Instead of the 185HP (2.5L) you are probably making 165HP +/-

inlinev said:

Where do you see this? The sky active engine was specifically designed to work with 87 octane.

Click to expand...

If you go to the SAE site where the engines are tested and achieve official numbers. They used 91 octane to get their peak HP/Torque #'s. I will try and find the link.

Yes, Mazda SkyActiv was designed to work with 87 octane BUT it does NOT achieve max/peak HP with 87 octane. If it's 95F outside and you have 4 people in the vehicle and climbing a hill. I guarantee you the computer is de-tuning the engine to prevent knock with 87 octane. Instead of the 185HP (2.5L) you are probably making 165HP +/-

If it is 60F outside with one person in the car on a flat level road with 87 octane, then it will make closer to the 185HP.

Fact is ALL engines will de-tune themselves without the driver ever even knowing it. The computer and sensors are constantly adjusting to conditions.

>If you go to the SAE site where the engine<

Which way was octane used measured RON, MON, or AKI (R+M)/2 ?

Since the SAE is international a link to that SAE page would be more enlightening.

MikeM. said:

That 10% ethanol will damage engine parts is an old wives tale created when fuel systems had rubber/plastic parts that were not alcohol resistant.

All late model cars are DESIGNED to be run on gasoline with 10% alcohol!

No damage will occur. None.

Click to expand...

Although ethanol does reduce the toxicity of car exhaust, it can also be very corrosive. Ethanol can absorb water and dirt very easily, and if those contaminants are not filtered out successfully, they can cause damage and corrosion inside the engine block. Fuel efficiency is also a consideration when considering the advantages of ethanol fuel. Ethanol, at least in its present form, does not appear to provide the same fuel efficiency as gasoline.

The problem is that ethanol free gas can be hard to find

inlinev said:

The light has nothing to do with the fuel octane rating. The vehicle will trigger the light if it detects a vacuum. Your gas cap just wasn't shut tightly.

Click to expand...

I took it off and put it back on several times, it didn't go out until I diluted it with regular gas. Coincidence, maybe....

Initial SkyActiv real world testing showed detonation when downshifting and passing on the highway. The actual "knock" was heard by engineers/testers back in 2011. They had to revamp and do some programming.

The quote was:
" In transitional throttle applications like tipping in quickly from steady state to brisk acceleration, like when passing a car or when making a quick turn from a standstill, we could hear the sharp crack of detonation. This only lasted an instant to two but it was unnerving."

Again, it is a 100% guaranteed fact the the SkyActiv engine will de-tune itself during certain conditions to prevent engine knock that is due to the high compression and low octane fuel. Hot outside temps, loaded CUV with cargo or 2-4 people, climbing a hill/grade. It will not be making 185hp (2.5L) under those conditions, that is a fact. The computer will de-tune it to prevent the engine from destroying itself with detonation/knock.

With that being said, IF you drive the vehicle in high outdoor temps, load the CUV with people or cargo and climb mountain grades. It is well worthwhile to fill up with 91 octane or better. It will definitely help the engine from de-tuning itself and give you the full 185HP. Putting around town, 87 octane is fine.

littlebear said:

If you go to the SAE site where the engines are tested and achieve official numbers. They used 91 octane to get their peak HP/Torque #'s. I will try and find the link.

Click to expand...

You may be confusing 91 RON with 87 pump octane. In the US pumps are marked with pump octane ratings. 87 on the pump is equal to approx. 91.5 RON (Research Octane Number)

Yes, Mazda SkyActiv was designed to work with 87 octane BUT it does NOT achieve max/peak HP with 87 octane. If it's 95F outside and you have 4 people in the vehicle and climbing a hill. I guarantee you the computer is de-tuning the engine to prevent knock with 87 octane. Instead of the 185HP (2.5L) you are probably making 165HP +/-

Click to expand...

All engines make less power at 95 degrees than they do at 60 degrees (regardless of the octane used). Only cars in which the manufacturers recommend premium benefit from premium. These are cars that are designed to run on premium but will self-adjust to run on regular. I know because I own one, a Volvo S80 T-6. I fuel it with premium but I've tried regular and it does make more power with premium, I can easily feel the difference. The Mazda does not fall into this class of cars. The CX-5 avoids knock by using a number of technologies and does not make more power with higher octane fuel (even if it's 95 degrees outside). Knock is avoided by controlling the flow of exhaust gases, changing the valve timing on the intake valves, exhaust valves or both, using a piston with a special little hole in the middle into which the direct injection charge is released, controlling head temperatures with sophisticated water cooling design, etc. etc. etc. While the CX-5 does change the fuel mixture and spark timing based upon ambient temperatures and pressures, the changes are based not on detecting knock but on the environmental conditions themselves. In other words, it will dial the spark timing back whether you have super-duper 95 octane in there or plain old 87 octane. It's designed not to knock with 87 octane and, if it detects knock, something has gone wrong. My Volvo, on the other hand, is always trying to make maximum power until it detects knock and then it dials back boost pressure and/or timing until it doesn't detect knock any longer. The CX-5 does not work this way and higher octane will not provide any more power (assuming there is nothing wrong with the engine like excessive carbon build-up, etc). The difference is the Volvo Manual says it can run fuels from 87 to 92 but recommends 92 all the time. The CX-5 manual recommends 87 pump octane(or higher). That's the way you can tell which style of knock management any given vehicle uses. The method my Volvo uses allows it to maximize power (268 HP from a 2.8L straight six but only when using premium) but it is also the more expensive and potentially more problematic method should something go wrong.

Fact is ALL engines will de-tune themselves without the driver ever even knowing it. The computer and sensors are constantly adjusting to conditions.

Click to expand...

True, all modern cars will de-tune to suit atmospheric conditions and will make more power with cooler air. But not all cars will "up-tune" just because they are not knocking. Two completely different strategies.

littlebear said:

Mazda gets its HP numbers for the SkyActiv engines with 91 Octane fuel. The factory SAE numbers were achieved with 91 octane fuel/

Engine will NOT make more HP than the factory rated #'s but it will DEFINITELY make less HP with 87 octane fuel in hot weather. Engine will "detune" itself when it sense knock.

Click to expand...

Your information is incorrect. SkyAciv-G 2.5L/2.0L are listed as 184/155 hp with lowered 13:1 compression ratio for regular gas in North America market wheras in other regions they're listed 5~8 more hp due to 14:1 compression ratio (not for 2.5L) for premium gas. Your statement is for engines where premium gasoline is required or recommended to reach manufacture claimed horsepower. But Mazda SkyActiv-G engines for NA market specifically tuned down for regular gas and rated as such. See this Car and Driver article for more details:

Mazda Skyactiv-G and Skyactiv-D Engines in Detail

littlebear said:

Initial SkyActiv real world testing showed detonation when downshifting and passing on the highway. The actual "knock" was heard by engineers/testers back in 2011. They had to revamp and do some programming.

Click to expand...

Don't be ridiculous! (attn) That's why they were driving a test car in 2011. The CX-5 released to the public is designed and tuned to not knock no matter what the atmospheric conditions are (as long as the fuel is at least 87 octane).

chckboy5 said:

Do you guys have a preference on which top tier gas to use?

Click to expand...

Although the base may be the same, but different brand of gasoline has different type of detergent pack. So my preference is based on type of detergent used and price. I like Shell Nitrogen Enriched Cleaning gasoline and feed our CX-5 with such. My second choice would be Chevron with Techron. Our poor CR-V gets Top-Tier Costco gas with Warren Buffett's Lubrizol detergent as it's cheaper.

MikeM. said:

True, all modern cars will de-tune to suit atmospheric conditions and will make more power with cooler air. But not all cars will "up-tune" just because they are not knocking. Two completely different strategies.

Click to expand...

Correct. The SkyActiv engine will NOT make any more power than the SAE verified 185HP (2.5L). That is the maximum HP the engine will make in IDEAL conditions. It will never make more HP BUT it can and will always make less HP in not ideal conditions.

Mazda engineers built in tons of "safety" factors to prevent detonation. Nothing would destroy Mazda's reliability and warranty claims than a high compression engine that detonates to death and falls apart with a hole in the piston or a spun rod bearing.

Here is the crux of it:
A - CX-5 with 4 people inside climbing a grade with 90F outside ambient air temps running 87 octane
VS
B - CX-5 with 4 people inside climbing a grade with 90F outside ambient air temps running 91 octane


Vehicle "B" will have more HP on tap as the computer will not de-tune as much as vehicle "A" since detonation will be inevitable with either options but vehicle "B" with 91 octane will be less prone to detonate and therefore de-tune itself

littlebear said:

Correct. The SkyActiv engine will NOT make any more power than the SAE verified 185HP (2.5L). That is the maximum HP the engine will make in IDEAL conditions. It will never make more HP BUT it can and will always make less HP in not ideal conditions.

Click to expand...

This is getting tiring. All engines make less than their rated power when the air is hot or less dense. Putting higher octane fuel is NOT going to magically produce more oxygen or more power (in an engine where the manufacturer recommends 87 octane).

Mazda engineers built in tons of "safety" factors to prevent detonation. Nothing would destroy Mazda's reliability and warranty claims than a high compression engine that detonates to death and falls apart with a hole in the piston or a spun rod bearing.

Click to expand...

There is only one safety factor built in to prevent detonation and that is the knock sensor. The engine is designed to not knock unless something goes wrong with one of the other systems. The engines computer knows when it's 90 degrees out, it knows what the coolant and oil temps are and it knows what the barometric pressure is. It also knows how much load is on the engine. Knowing all this, it assumes you have octane as low as 87 (or a little lower as a safety margin) and then it adjusts the timing and other parameters to values which will not cause detonation. It will never know if you filled the tank with 100 octane aviation gasoline, it has no way to know.

The knock sensor would only come into play if you "surprised" it with octane below 87, or, for whatever reason, carbon had built up in the combustion chamber or one of the sensors was providing bad data. If your CX-5 is running properly the knock sensor will never hear a knock, even if it's 120 degrees out. The knock sensor is only there as a fail-safe. What is it that you don't understand about that?

Here is the crux of it:
A - CX-5 with 4 people inside climbing a grade with 90F outside ambient air temps running 87 octane
VS
B - CX-5 with 4 people inside climbing a grade with 90F outside ambient air temps running 91 octane


Vehicle "B" will have more HP on tap as the computer will not de-tune as much as vehicle "A" since detonation will be inevitable with either options but vehicle "B" with 91 octane will be less prone to detonate and therefore de-tune itself

Click to expand...

Where's your evidence of this? (blah)

MikeM. said:

The knock sensor would only come into play if you "surprised" it with octane below 87, or, for whatever reason, carbon had built up in the combustion chamber or one of the sensors was providing bad data. If your CX-5 is running properly the knock sensor will never hear a knock, even if it's 120 degrees out. The knock sensor is only there as a fail-safe. What is it that you don't understand about that?

Click to expand...

We will just have to agree to disagree. It's not worth debating over. I leave with this from Motor Trend:

If the engine is tuned for regular but fueled with something of higher octane, things are a tad more complex. Most modern knock-sensed ignitions seek MBT timing and thus, at least in theory, profit from the added octane. Some, though, have preset ceilings beyond which they won't advance. These days, our engines' electronic control units select optimal timing. What's more, modern engines have knock sensors listening for incipient ping. If detected, they dial back ever so slightly on ignition timing to eliminate it even before it's audible to the likes of us.

littlebear said:

We will just have to agree to disagree. It's not worth debating over. I leave with this from Motor Trend:

Click to expand...

Uh... your quote is from Road and Track, not Motor Trend. And that article you quoted from has something more specific to our CX-5's than the blurb you posted from the same article.



It's unclear to me why you quoted the part that said "If the engine is tuned for regular but fueled with something of higher octane, things are a tad more complex. Most modern knock-sensed ignitions seek MBT timing and thus, at least in theory, profit from the added octane."

Notice the part of the article you quoted says "Most modern knock-sensed ignitions" but that the same article goes on to address specific examples. And I quote:

Mazda's new SkyActiv engine family is exemplary of the trend for higher efficiency and also of marketing considerations. Direct injection, artful design of piston geometry and other nuances give our Mazda3's SkyActiv powerplant an octane appetite for regular; this, despite its 13.0:1 compression ratio. The Euro version gets an even loftier 14.0:1 with commensurate enhancements of power and efficiency—but also with a premium fuel requirement unwarranted for the North American market.

Click to expand...

Given the context of this article (discussing whether running premium in an engine designed for regular is of any benefit) I would say the phrase "a premium fuel requirement unwarranted for the North American market." means exactly what it says - there is no benefit to running premium fuel in a North American Skyactiv engine. And it's precisely because of it's "artful design of piston geometry and other nuances" that premium is unwarranted.

This is from the same article you tried to use to prove your point. So it's unclear to me why you still believe the fallacy that at "90 degrees F" while "climbing a steep hill" the CX-5 all of a sudden benefits from a fuel it was not designed or tuned for.

MikeM. said:

This is getting tiring. All engines make less than their rated power when the air is hot or dense. Putting higher octane fuel is NOT going to magically produce more oxygen or more power (in an engine where the manufacturer recommends 87 octane).

Click to expand...

No, but higher octane in those conditions may reduce the degree of timing retardation the engines PCM will dictate if it starts to detect knock. Suboptimal timing retardation reduces power.

davefr said:

No, but higher octane in those conditions may reduce the degree of timing retardation the engines PCM will dictate if it starts to detect knock. Suboptimal timing retardation reduces power.

Click to expand...

(attention)

littlebear said:

If you go to the SAE site where the engines are tested and achieve official numbers. They used 91 octane to get their peak HP/Torque #'s....

Click to expand...

I'd suspect they use 91 octane in order to control the testing conditions since some engines do require the higher octane.

Then it could be just unclear about RON/MON/AKI as noted elsewhere in the thread.