This is the paragraph that meant the most to me.Octane is a measure of a fuel's 'flashpoint'. That is at what temperature and pressure that fuel (in a vapor) will ignite. With lower octane fuel there is a wider range of pressures and temperatures where the fuel will ignite. This allows for a much less predictable piston location where the fuel will actually start to combust. [ ... ] Fortunately, higher octane fuel narrows the range of temperatures and pressures where it's vapor will actually ignite.
Once again, using an octane higher than what is recommended in the owner's manual does absolutely nothing to increase performance if it was not tuned for it. Perhaps you think you know more than the engineers who designed your Jeep. The placebo effect is strong with this one, Yoda.Wow, sometimes it's just not possible to get through to some people.
Please by all means run whatever fuel you care to. It's your engine treat it however you damn well want.
I spent a good part of my career as a Powertrain Software Engineer with Chrysler. For over a decade and only moved on to another great software development opportunity near Denver CO. Do I miss Michigan? Not in the slightest. Do I miss developing and calibrating Engine Controllers? Probably by far the most interesting and rewarding product development program I've ever worked on.
I've implemented many fuel delivery, spark timing, EGR, Auto Idle and a boatload of federally mandated OBDII emissions monitors. One of the primary concerns that is always evaluated is the quality of the fuel used. There used to be at one time a long thin stainless steel tube and other sensors to help determine gasoline viscosity, octane and ethanol content in order to select the best 'tuning' parameters for any sensed fuel condition.
However, that was both expensive and sometimes unreliable. It's remarkable the differences in fuel quality from different grades, seasonal additives, detergents, ethanol content, and yes, even octane from all the different suppliers, distributors and retailers. If you think fuel is the same everywhere, you're pretty foolishly naive.
Yet, your engine has to adapt and be able to cope with any of it...
In more modern engine designs, those fuel quality sensors have been thrifted away with more sophisticated algorithms which monitor engine metrics, such as power, temperature, various air pressures, knock but mostly emissions by-products via both the upstream and downstream O2 sensors.
While many particulates like Carbon Monoxide (CO), Nitrous Oxide (NO2) and others aren't directly detected, the overall amount of O2 or lack thereof, can infer quite a lot of information of the quality of the combustion events.
In these more sophisticated schemes, a reference standard is measured from all these various engine metrics in order to produce a specified performance goal. But this is based upon using a very high quality fuel (that you typically can't buy on the consumer market) as a baseline. This is the top of the line quality fuel that all others are compared to.
As these performance metrics degrade with the introduction of lower quality fuels, the engine controller tries to continue to achieve the very lowest amount of emissions typically sacrificing even more performance. It does this by 'de-tuning' things such as fuel-to-air ratio, spark timing, idle speed setpoints, exhaust gas recirculation among others. Recall, the EPA rules.
Typically, the lower the fuel quality the lower the performance in order to achieve a federally regulated emissions output goal. This should be obvious.
While octane itself, is a small factor to the overall quality of the gasoline purchased, the lower the octane, the less reliable the ignition flashpoint becomes. The spark timing equations become less 'predictable'. A natural by-product of this is pre-detonation which causes knock. Any knock, of any amount is DETRIMENTAL to the well being of your piston rings and cylinder wall surfaces. Knock creates violent vibrations that cause excessive wear that will lower compression over time.
Higher octane fuels dramatically lowers the potential of knock because it's flashpoint is much more precise for a given temperature and pressure threshold within the spark chamber. The engine controller can therefore better predict what the optimal ignition point is going to be and adjust the spark timing to it's most optimal position of the piston after Top Dead Center (not before). Hence a much lower probability of pre-detonation (knock).
So while lower octane by itself doesn't necessarily lower the overall fuel's quality, it doesn't help. The only factor you as a consumer can control at the pump is octane. However, the lower the octane, typically also the lower the grade (overall quality) of the gasoline offered. The higher priced grades of fuels are not just due to octane alone, but they're marketed that way as an easy number to indicate at the pump, besides just price.
Furthermore, all auto manufactures selling 'afforfable' vehicles for the masses specify the use of lower octane fuels as a way to advertise a lower cost of ownership. Nothing more. No science whatsoever to what's printed in the owners manual. Pure propaganda. The science all boils down to each and every combustion event in real time.
So go ahead, continue to put grape juice in your jalopy. Psychologically feel good at pressing the button for the cheapest, lowest quality fuel at the pump. I'll however follow the science and get another 350K+ miles from my current engine.
I'll bet you didn't read this post in it's entirety. Tl;Dr. Too long; Didn't read. Well pal, not only did I read them, I've also wrote a few of them and better yet, I've lived and helped developed lots of the engine controllers on the road.
There's a pretty decent chance that either you or someone you know has driven a vehicle running with some of my Engine Controller software. I'm pretty proud of that, whether or not anyone reads anything on this forum.
Jay
uuuuuhhh....did you read the part about how he actually was one of those engineers...?Perhaps you think you know more than the engineers who designed your Jeep.
I'd be interested in those "official" studies.I could post more links to official studies but I doubt it would make any difference to you.
What part of ”for optimal performance” from the manual makes anyone think that Jeep is not recommending or tuning for 91 octane? Will it run on 87? Of course. Will it have better performance on 91 octane? Even according to the manufacturer, YES. Is it enough of a difference to feel in day to day cruising? Probably not. Will it make a difference in high altitudes, hot days, towing, or blasting up a steep loose hill/ through deep sticky mud/ or making first tracks in deep powder? Most likely yes. You can run whatever you want, but Jeep absolutely does recommend 91 octane in black and white. Mazda and Ford actually publish different power figures for their turbo engines. Mazda gains 23hp and 10ftlbs from 87-93octane. Car and driver tested the F150 eco boost extensively and showed a 20hp difference. 0.6 second quicker 0-60 and a half second quicker 1/4 mile time by a simple octane change. These are not NA engines from the 90’s with no built in tuning adjustments to take advantage of octane increases. That’s not opinion, butt dyno, or emotion, it’s measurable fact period. https://fordauthority.com/2019/08/is-premium-fuel-better-in-an-ecoboost-ford-f-150/Once again, using an octane higher than what is recommended in the owner's manual does absolutely nothing to increase performance if it was not tuned for it. Perhaps you think you know more than the engineers who designed your Jeep. The placebo effect is strong with this one, Yoda.
Also, using a higher octane than what is recommended to reduce knock is just putting a Band-aide on a larger problem that should be corrected.
I could post more links to official studies but I doubt it would make any difference to you.
John,I guess this settles it. The intranets have spoken and now we know. No need to listen to people that make a living at doing calibrations, the armchair calibrators know better. Seat of the pants is much better than data. As we all know, manufacturers just design and build a vehicle, then never do real world testing. They know every owner will ask for the best of the best and use it religiously. I bet all of the 2018 2.0T motors from 2018 in a Jeep with 200K on the clock, have grenaded by now. They have never posted here because they are embarrassed that they threw in regular gas as opposed to premium.
We have a customer with a 2018 and it just hit 200K on his 2.0T Wrangler. He uses our non Mopar oil filters, the non Mopar oil and he runs regular in it. I'll let you know when it blows up as he's doing it the wrong way.
What is better? Do you need to use the best of the best for everything? When I see older vehicles, the motor is the one thing that outlasts the rest of the vehicle. Yet on the intranets, we obsess about the internally lubricated engine parts and what gas we put in it.John,
Not to belabor anything further but the thought becomes "could he have even done better?"
The answer always comes down to "how good is good enough?"
Everyone personally has the absolutely correct right to answer that for themselves. But at least (I hope) some education may have transpired where people may now make a more informed decision.
The concept of a better decision is still up to them.
Jay
As you can tell from the overall conversation in this thread that opinions will be all across the entire spectrum regarding using 87 or higher octane fuels. But since you're asking me, I'll be consistent with my answer.@jeepoch How does this effect the 4xe? The supplemental manual states to run 87 octane (no benefit stated for higher) and I can only assume that the "boost" from the electric motors is the reason. Does this mean that Jeep re-tuned the 2.0L for the 4xe? Or might I still see an advantage with 91 even with the electric motors?