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Since the pumps in Canada display the AKI, I believe a RON of 98 would translate to what I would see as 93 on a pump here. I use a Chevron 94 AKI pretty much exclusively when I'm at home in Calgary, and when on the road try to avoid anything less than 91. Is that study inferring that 98 RON introduces so much engine knock that its killing performance? Seems odd, but there are other folks on the forum much more versed in fuel distinctions than I am, and they may be able to shed more light on what you've found.

Let's just say I'm confused as the owner manual clearly states the recommended use of premium fuels, which would be exactly in that 98 RON range. I have to be missing something in the big picture here.
 
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Discussion Starter · #3 · (Edited)
Since the pumps in Canada display the AKI, I believe a RON of 98 would translate to what I would see as 93 on a pump here. I use a Chevron 94 AKI pretty much exclusively when I'm at home in Calgary, and when on the road try to avoid anything less than 91. Is that study inferring that 98 RON introduces so much engine knock that its killing performance? Seems odd, but there are other folks on the forum much more versed in fuel distinctions than I am, and they may be able to shed more light on what you've found.

Let's just say I'm confused as the owner manual clearly states the recommended use of premium fuels, which would be exactly in that 98 RON range. I have to be missing something in the big picture here.
I am very confused because this is only on this motor. Can it be the multiair ? or is a calibration issue like spark plug gap ,ignition timing, and so...
Also if you look on audi a3 there you will see more fuel burned but got more power. Strange !
Also from what i read the mfc recommend 98 RON .
98 RON =87-88 MON(USA)=93AKI
 

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I have been using 91 octane in Quebec and Ontario, mind you some services only have 87 reg, 89 mid and 91 super. Yes there are other have a 93. But 91 is good for my Spider belly.
 
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I have been using 91 octane in Quebec and Ontario, mind you some services only have 87 reg, 89 mid and 91 super. Yes there are other have a 93. But 91 is good for my Spider belly.
I have used Race Gas to boost my octane from 91 to 95, and can verify that Spidey very much likes that juice. But it's a bloody expensive way to get there. So when I found a local Chevron that sells a 94, that's now my favourite place to fuel up. Unfortunately, in Alberta, 91 for premium is pretty much the norm. When I drive across Canada, there's one point as I'm crossing through Ontario where I have no choice but to fuel up in a location that only sells regular (yikes). I can attest that the car does not like lower octane fuel, and responds accordingly. The wild card with all this is that we, like many others, are running a tune.... so that would affect our engine's performance characteristics such that they don't mirror what might be seen in a stock setup.
 

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Maybe this will help explain a few things, or maybe it will just add to the confusion . . . I'm just hoping it helps everybody get the correct fuel in their cars - keep in mind that those 124 Spiders with a stock tune want a minimum 91 octane rating (R+M)/2. Also, please seek out "Top Tier" gasolines. So for an explanation of Octane, please see " www.eia.gov/energyexplained/gasoline/ " . Also click on "Octane in Depth" in the above link. Please keep in mind that using too low an octane fuel can result in engine damage. The engine control system in modern cars utilize a knock sensor, and the PCM controls timing and fuel delivery as needed - but there are limitations to this system. So, using too low of an octane rating can be bad for your engine. Also, using too high of an octane rating can also be detrimental. As octane rating is a measure of what temperature/pressure gasoline burns at, too high of an octane rating could potentially result in incomplete combustion. This, in turn, may foul an 02 sensor, compromise the effectiveness of a catalytic converter, and/or cause some carbon buildup in the cylinders. Please note: in no way am I suggesting that, say, a 95 octane fuel will harm our engines, esp. if it has had a "tune" but the potential may exist. In the case of a "tune" I would be tempted to consult the provider of your particular tune. For stock cars, I would stick with 91 to 93 Octane as recommended regardless of a promised miniscule change in power output or fuel economy. Just my opinion. Hope all this helps folks - that's all I'm trying to do. Happy Spidering, s.
 

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On my post on another thread, I said that 93 octane fuel was not available in Orange County / Southern California. Apparently there are a few stations that carry 93 octane (very few) but none near me in the LB. There are a few a hike away that sell 100 octane racing fuel but I would not put that in my Spider. So for the most part, I am stuck with 91 octane fuel. I use Chevron or Shell gas because those are Top Tier rated. The Spider's owner's manual says to use only Top Tier rated fuel. I did find a Chevron station out beyond Lost Wages that has had historically bad gas. My car (not the Spider, a since sold ML350) choked badly on that station's offering. I know of one person who habitually put 87 octane fuel in her ML350. Needless to say, it died an early death.
 

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Hi @DougGTR , I am not sure just what is offered out your way, but here all grades of both Shell and Mobil are Top Tier rated, and both have 93 Octane. Hope this helps! Best, s.
 

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The list shows just about everyone. I don't recall seeing stickers on pumps. Maybe better to know how to avoid stations that don't sell it?

 

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I don't see stickers on all the pumps either, and if you ask the people who work at gas stations if their product is "Top Tier" you are greeted with a blank stare. However, the list on the Top Tier website is accurate to the best I can tell. Note that there are some major suppliers not listed (such as Gulf). We had a manufacturers engineer here about 2 years back that did chemical tests on several different brands of fuel for detergent. Mobil, Shell, and Citgo all showed significant detergents, Gulf had none. This in itself showed me the list on the Top Tier website is accurate - at least the best we can get. s. P.S.: I would avoid any place not on Top Tiers list, including 'No Name Brand' gas stations and corner stores.
 

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Neither Shell nor Mobil offer 93 octane regularly in SoCal. Here is a website for finding 93 octane (or higher) fuel.
THANK YOU FOR THIS LINK!
I didn't know anything better than 91 was available in my area and wouldn't mind giving 93 a go.
Shortly after buying me spider I asked both the Fiat mechanic and my local shop the same silly question, what do you think is the best gas for these motors you're working on? They both gave the same answer! Chevron first, then Shell. Weird.
 

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Also, using too high of an octane rating can also be detrimental. As octane rating is a measure of what temperature/pressure gasoline burns at, too high of an octane rating could potentially result in incomplete combustion.
That's not correct. Octane rating or number is the result of testing a sample of gasoline and finding out what blend of iso-octane (2,2,4-trimethylpentane, defined as 100 RON) and n-heptane (defined as 0 RON) gives the same knock intensity under standard conditions. For example 91 RON means the fuel gives the same knock intensity as a blend of 91% isooctane plus 9% heptane. RON is "research octane number" and is similar to MON (motor octane number), the two tests are carried out the same way but RON is done at 600rpm whilst MON is at 900rpm. ASTM test methods are D2699 and D2700 for RON and MON (or similar ISO tests 5164 and 5163)

Modern car engines can take advantage of higher octane fuel by adjusting timing but once at a limit, higher octane is a waste of money. Octane is neither a measure of energy content nor fuel efficiency, just resistance to knocking.
 

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Discussion Starter · #14 · (Edited)
Maybe this will help explain a few things, or maybe it will just add to the confusion . . . I'm just hoping it helps everybody get the correct fuel in their cars - keep in mind that those 124 Spiders with a stock tune want a minimum 91 octane rating (R+M)/2. Also, please seek out "Top Tier" gasolines. So for an explanation of Octane, please see " www.eia.gov/energyexplained/gasoline/ " . Also click on "Octane in Depth" in the above link. Please keep in mind that using too low an octane fuel can result in engine damage. The engine control system in modern cars utilize a knock sensor, and the PCM controls timing and fuel delivery as needed - but there are limitations to this system. So, using too low of an octane rating can be bad for your engine. Also, using too high of an octane rating can also be detrimental. As octane rating is a measure of what temperature/pressure gasoline burns at, too high of an octane rating could potentially result in incomplete combustion. This, in turn, may foul an 02 sensor, compromise the effectiveness of a catalytic converter, and/or cause some carbon buildup in the cylinders. Please note: in no way am I suggesting that, say, a 95 octane fuel will harm our engines, esp. if it has had a "tune" but the potential may exist. In the case of a "tune" I would be tempted to consult the provider of your particular tune. For stock cars, I would stick with 91 to 93 Octane as recommended regardless of a promised miniscule change in power output or fuel economy. Just my opinion. Hope all this helps folks - that's all I'm trying to do. Happy Spidering, s.
Hi Steve
Your explanation about octane and the influence on engine is perfect but known.
This wasn't the point on my post.
In Europe we use 95 as premium and 98 as super.
The manufacture ignition timing is for 98 with lower limit till 95 .
Regards this research i understand that 95 octane for 1.4 l multi-air engine did better than 98.
This is the paradox that confuse me because is known that 98 octane can be compress more than 95 and if the engine ignition timing is mapped for it i don't understand why the result is showing the opposite.
The second issue is the result in compare with other cars on research as Audi A3.
I am running on stock with 95 . I tried 98 and nothing change (12 km more for a tank and the hole in the pocket)
For cars with bigger turbos and increased inter coolers maybe 98 octane is a must and for sure with an other map.
My question is why there is no increase in power using 98 .
 

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That's not correct. Octane rating or number is the result of testing a sample of gasoline and finding out what blend of iso-octane (2,2,4-trimethylpentane, defined as 100 RON) and n-heptane (defined as 0 RON) gives the same knock intensity under standard conditions. For example 91 RON means the fuel gives the same knock intensity as a blend of 91% isooctane plus 9% heptane. RON is "research octane number" and is similar to MON (motor octane number), the two tests are carried out the same way but RON is done at 600rpm whilst MON is at 900rpm. ASTM test methods are D2699 and D2700 for RON and MON (or similar ISO tests 5164 and 5163)

Modern car engines can take advantage of higher octane fuel by adjusting timing but once at a limit, higher octane is a waste of money. Octane is neither a measure of energy content nor fuel efficiency, just resistance to knocking.
I'm not quite sure what you are referring to when you say that is "not correct". As a low octane fuel ignites more easily than a high octane fuel, the potential exists for incomplete combustion at octane levels that get too high. That can lead to cat problems, etc. I am not saying this WILL happen with our cars, but that it could depending on how high of an octane you go. This is based on what I have been taught by instructors in manufacturers schools where some instructors are engineers in the area they teach in. Hmmm . . .
 

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What I mean is that when you say "octane rating is a measure of what temperature/pressure gasoline burns at" - that is not correct. Octane rating is a comparison of knock intensity with reference fuel blends (octane/heptane).

One other thing to remember is that in the US and Canada, the octane number posted on the pump is (RON+MON)/2 (sometimes called "road" octane, or AKI anti-knock index) whereas everywhere else on the world, only RON is referenced. Typically MON is around 10 points lower that RON (it will depend on the nature and relative quantities of the various refinery streams that are blended onto the gasoline), so for example "regular" 95 RON in Europe is equivalent to around 90 road/AKI and "premium" 98 or 99 RON is equivalent to 93-94 road/AKI. And that's pretty much it for the choice of gasoline in Europe, just 2 grades that vary little from country to country.

Oh, and BTW I am a (chemical) engineer in the field (of oil refining and petrochemicals)
 

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My question is why there is no increase in power using 98 .
Because octane is not a measure of energy content or ultimate power produced, it's just a measure of knock-resistance. In fact there is no specification for energy content, you just get what you get!
 
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...and whilist 98 RON gasoline can be compressed more than 95 RON until the same knock intensity is reached, engines don't have variable compression ratio, and air flow is pretty much fixed. The only variable is the ignition advance which in theory can be increased with higher octane fuel and potentially create more power, but only if the ECU is programmed to do that (which an aftermarket "tune" is specifically designed to do). It could be that the standard ECUs in the cars in the AAA test have different expectations on the range of fuel octane.
 
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Hi @azzura , OK, so I understand that my statement "octane rating is a measure of what temperature/pressure gasoline burns at" is what you say is incorrect. Your knowledge of this subject certainly trumps (no pun) mine, and I fully respect that. So please let me explain what I was trying to say, in a different way, in hopes of being more accurate (as my only goal here is to help my fellow Spider owners and others who may be interested), and tell me what you then think.
It is a given that a low octane rated fuel, say 87 octane using the (R+M)/2 standard will ignite and burn at a lower temperature than a 94 octane, and that pressure (compression in an engine) greatly increases the temperature. Conversely, the 94 octane gasoline requires higher temperature and pressure (compression) to burn than the 87 octane gasoline. Hence, the temperature/pressure statement. Maybe I was trying to be overly simplistic? Trying to get a point across that maybe one should seek out the proper octane rated gasoline for their particular engine and intended use? What I was trying to say was "Low octane rated gasolines burns at lower temperatures and pressures than a high octane rated gasoline" . I agree that octane is an indicator of, or a measure of, a particular gasolines blend to resist knocking (also called spark knock, or pre-ignition) and is useful in comparing fuels. And, I agree that the octane numbers are shown as a comparison to standard reference gasolines that have octane numbers of 0 (having no resistance to knock in a test engine) and 100 (a reference blend having a lot of resistance to knocking).* Further agreed that a vehicles management system can compensate for knock to a certain degree by altering spark timing and other things, but there is a limit.
While I am writing this I might as well add that using MMT's (Manganese Fuel Additive for short , a.k.a. octane boosters) is discouraged by Fiat, and mentioned in our U.S. owners manuals. MMT's are thought to shorten spark plug life as well as damaging catalytic converters and other issues like those I have noted above. The use of MMT's in gasoline supplies in the U.S. is prohibited, but one can purchase octane boosters over the counter. I'm not sure what the situation is in Great Britain or Europe as far as buying these products over the counter, but please weigh in on this @azzura. Your input is appreciated. Best, s.

* An octane rating of, say, 101 will resist knocking more than that of the standard.
 

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Hi Steve
Your explanation about octane and the influence on engine is perfect but known.
This wasn't the point on my post.
In Europe we use 95 as premium and 98 as super.
The manufacture ignition timing is for 98 with lower limit till 95 .
Regards this research i understand that 95 octane for 1.4 l multi-air engine did better than 98.
This is the paradox that confuse me because is known that 98 octane can be compress more than 95 and if the engine ignition timing is mapped for it i don't understand why the result is showing the opposite.
The second issue is the result in compare with other cars on research as Audi A3.
I am running on stock with 95 . I tried 98 and nothing change (12 km more for a tank and the hole in the pocket)
For cars with bigger turbos and increased inter coolers maybe 98 octane is a must and for sure with an other map.
My question is why there is no increase in power using 98 .
I am sorry, ADI, for not directly addressing the issue. What I was trying to do was to get across a simplistic explanation of octane. And I guess I failed a bit at that.
For the loss of power issue with a higher octane? I agree completely with @azzura when he said above that octane was not a measure of power, that you "get what you get". I can venture a guess, and it is only a guess, because I do not know for sure but maybe that Renegade has a 1.4L with a lower compression ratio than our Spider engines, or some other variation that may want only a regular grade of fuel? Best, s.
 
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