Do we have to run premium?

[srt20]

Hopefully this thread is dead.







I'll see all you guys next week when it gets brought up again.

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[chevymitchell]

Jeezus you guys are slow.

Less octane has the potential to make less power because of ECU mapping due to preignition.

The BTU of all pump gas fuels is the same.


End this shit!

A little back and forth is healthy for uneducated minds. The majority of people on here aren't sure what the (R+M)/2 is let alone understand what a BTU is and how to use it in a calculation. I can appreciate that you do. Instead of approaching the conversation like this, you could offer up another professional perspective and help make this something people can read and learn from.

I love the "end this shit" at the end. Lol. That was cute. First time on the internet?

 

[srt20]

A little back and forth is healthy for uneducated minds. The majority of people on here aren't sure what the (R+M)/2 is let alone understand what a BTU is and how to use it in a calculation. I can appreciate that you do. Instead of approaching the conversation like this, you could offer up another professional perspective and help make this something people can read and learn from.

I love the "end this shit" at the end. Lol. That was cute. First time on the internet?

So all this shit isn't discussed every week?
You and that other dude are arguing 2 different things to arrive at the same conclusion......LMAO Somebody has to be stern with folks like you.

 

[chevymitchell]

So all this shit isn't discussed every week?
You and that other dude are arguing 2 different things to arrive at the same conclusion......LMAO Somebody has to be stern with folks like you.

It will likely be discussed every week because people are too lazy to search through the forums. It's the same with gearing, as well. The 4.88/5.13 conversation is just as much fun to have. Lol. It's not enough to give short answers. People will argue the holes or unassumed points. I gave many examples. I can't just come out and say the BTU's are the same. Then someone will bring up E85. Haha. It's a pump gas and it's not the same as the rest. I do agree... we'll talk about it again next week. and the month after that. and the week after that. Most people don't even look at the manual, let alone search the forum. However, this octane conversation is lateral to every corner of the gearhead world and has been around for a very long time. It'll never go away. Just wait until people learn that nitrous isn't flammable. Lol.

 

[neil]

I would rather a tank of non ethanol 87 than ethanol 93.

I buy non ethanol when out rurally and it's quite better mpg. But this is usually 89 or higher.

 

[N875ED]

Chevymitchell:

Octane DOES have much to do with power. The OBDII computer detects knock relative to the fuel's octane, and advances the spark timing up to the onset of engine knock. By advancing the spark, the combustion pressure increases and so does horsepower.

Piston aircraft engines in WW2 required fuel with somewhere around 130 octane (courtesy of buckets of tetraethyl lead added at the refinery) due to their high compression ratio, which was the way to get higher horsepower with a relatively lighter engine.

 

[chevymitchell]

Chevymitchell:

Octane DOES have much to do with power. The OBDII computer detects knock relative to the fuel's octane, and advances the spark timing up to the onset of engine knock. By advancing the spark, the combustion pressure increases and so does horsepower.

Piston aircraft engines in WW2 required fuel with somewhere around 130 octane (courtesy of buckets of tetraethyl lead added at the refinery) due to their high compression ratio, which was the way to get higher horsepower with a relatively lighter engine.

Let this die, please. Lol. No need to explain to me how this works. Please read the whole thread then start a new one if this is something you feel strongly about. This one is dead.

Like I mentioned before, it's only a prerequisite. Hemmings, Amsoil, Edelbrock, and any gearhead knows it doesn't make power. Please read the entire thread or Google it. It's very simple to understand.

I've unfollowed and ignored this thread now.

@srt20 Took a little longer than a week. Lol!

https://www.amsoil.com/newsstand/articles/high-octane-gas-boost-performance/

 

[randeeezy]

David,

I used to be a Powertrain Software Engineer for Chrysler back on the 2000 through 2008 model year programs. I helped design and implement quite a bit of the software on their Small Car, Large Car and Jeep/Truck Engine Control Module programs back then. And candidly, I had only left that really phenomenal gig in Auburn Hills, MI to move to the Front Range of Colorado. I still design and develop really cool software, just no longer for the automotive industry. However I feel I'm still qualified to answer your question.

As a matter of personal opinion (with some inside knowledge), I'm quite certain the owner's manual specifies using the lower octane (lower cost) fuel simply as a subtle mechanism to promote a lower cost of ownership for it's vehicles. If it did mention the possible range of fuels, or to use only the best possible fuel, may possibly turn some potential buyers off. Yet regardless of their reasons, they can certainly do a better job in trying to minimize the confusion on this subject. I suspect that their market research explicitly determined to avoid this subject altogether.

First, the car company needs to certify both emissions and fuel economy based on worst case fuel specifications, not the best. Second, there are indeed installed systems on the engine designed to detect knock dynamically (on-the-fly) in real time and adjust various engine parameters to decrease the amount of knock sensed. It does this through both dedicated knock sensors and engine performance metrics. The parameters adjusted are typically spark timing and fuel injector pulsewidth. There are other variables as well but this detail isn't really that important for our overall (informal) discussion. The physics and the implemented algorithms are indeed way more sophisticated than what I'm simply describing here.

However, while the engine can certainly 'react' to limit knock as it happens it is still nonetheless 'after-the-fact' of the knock event itself. In other words, the knock prevention algorithms only work after these conditions have happened to begin with.

The theoretical goal is to prevent any knock in the first place. Engine knock of any type or amount is DETRIMENTAL in some way. Knock is caused by improper detonation which works against the mechanics of the crankshaft's rotation. So rather than contributing to the engine's overall power output (torque) any knock at all, no matter how small, is retarding it. Unfortunately, this improper detonation can also cause piston damage (due to the unintended mechanical vibrations from the knock itself). These vibrations are acting on the piston and the rings causing excessive and undesireable wear on the piston's walls (all of it's sliding surfaces).

Suscinctly stated, the best possible internal combustion operation is therefore to NEVER have any knock whatsoever in the first place, period.

Another misconception is that octane is a measure of a fuel's energy content. This is false. Octane is a measure of the fuel's ignition flashpoint. The higher the octane value, the more consistent the pressure and temperature needs to be in order to ignite. It's a measure of the fuel's ability to combust at the exact same flash-point threshold reliably. The lower the octane, the larger the range of pressure and temperature values where this flash-point may occur.

Therefore the higher the octane, the more consistent this threshold is where the fuel actually ignites. The more consistent this is the easier it is for the engine controller software to determine and maintain the best possible spark timing, using the smallest possible injector pulsewidth (least amount of fuel) to produce the desired output torque based on accelerator pedal position (demanded speed).

Again with lower octane fuel, it's ignition flash-point is less consistent and the 'predicted' spark timing or pulsewidth calculation for each cylinder may not be as accurate for each particular combustion event. If this prediction is ever even slightly wrong, improper combustion can occur leading to a knock condition. So in theory, anything that can contribute to a more accurate combustion equation, where the spark is delivered to the piston's stroke in the most optimal position, lowers the probability for a knock event in the first place.

Recall, the engine controller software must always readjust it's variables to predict the spark timing for the next combustion event based on what it currently sensed for this as well as statistical calculations from some number of previous events. The more consistent these dynamics are, the smaller the adjustment required between events and the better the engine performs.

In summary, using premium fuel regardless of what they recommend and independent of whether you can afford it, will always be in both you and your engine's best interest.

I personally always use premium fuel and full synthetic oils (different topic). However, I achieved almost 300,000 miles on my previous vehicle, a 2005 Dodge Grand Caravan. The only thing that was not stock on it's 3.3L engine was a replaced water pump and an EGR valve. I might still be driving it if a distracted 16 year old on his phone hadn't pulled out into traffic. Luckily I swerved at 40mph, or he would have been T-boned. No one was injured but both vehicles were totaled. It's the reason I now have this wonderful JL Sport. I'm truly intending to put even more miles on this vehicle.

Hope this helps.
Jay

great and informative post, I'm reading it a year later but wondering if you think the 2.0 has the potential (if well maintained) to reach that kind of mileage, or if the 3.6 is the better long-term option?

 

[Iowa_Wrangler]

Anything without Ethanol! My manual says 91 is recommended.

 

[entropy]

I remember about 10 years ago in Thermo 101 class. We had an entire hour class about this. compression ratio, turbo engines, and octane. This was 10 years ago and it was explained to us, through science, how this all works. It was a fun week, we looked at the otto engine (which I remember this is where automobile word comes from), diesel, regenerative braking, turbochargers, etc... all of the different cycles. I dont remember shit now. All I remember is that higher octane was created to increase the temperature at which it starts to burn. To reduce knocking from high compression engine. Knocking is literally an explosion, and bad for the engine. And that's it. It is old science, it is all in an introductory engineering thermodynamics book, I have it somewhere might pull it out for fun to see if I can remember.

If our computers can now, through logic, reduce knocking. Then let it go, you can use 87. But people keep wasting their money at the pump, because some slimy business people had the great idea to call higher octane gasoline "premium". Watcha gonna do.

 

[W4V3]

Not to revive a dead horse, but has any consideration been given to the new requirements for the start/stop system? Were the compression ratios changed for this functionality? I'm running 87 in my 2020 3.6 and it runs fine.

 

[entropy]

Not to revive a dead horse, but has any consideration been given to the new requirements for the start/stop system? Were the compression ratios changed for this functionality? I'm running 87 in my 2020 3.6 and it runs fine.

Hahahahah yeah I looked into this a few months ago. I checked online and realized the compression ratio of the 3.6 on the JL is higher than the 2.0 turbo . It was a mindfuck moment for me.

To your question. I think the whole timing thing people are discussing, with the ECU adjusting to avoid knocking is negligible. What I mean is, you wont notice any improvements in performance. There is a possibility that at very high loads you might notice a difference (towing).

The reality is that if your engine isn't knocking, then everything is safe and you don't need to worry about reliability. People saying you might get an increase in power; those people have a point. People saying that your engine is gonna last longer on premium gas are full of it.

I personally wasted money to see what happened with higher octane gas once I found out my compression ratio. It didn't do anything. Absolutely the same as 87.

Do you wanna pay extra money to get an increase .5% performance driving around town or highway? it is negligible and a waste of money.

The people claiming 10%~20% increase in power have absolutely no data to prove this. It is all speculation, I felt this, I felt that, I saw Jesus. I had a dream with Riley Reid after I filled my Jeep with premium gas. It is all speculation and fantasy to a point.

 

[jmccorm]

Do you wanna pay extra money to get an increase .5% performance driving around town or highway? it is negligible and a waste of money.

The performance improvement from higher octane gas was significant enough that Jeep wrote about this very topic in the manual...

...but Jeep doesn't say by how much higher octane will increase performance, do they? Just that it does by some noticeable amount.

I stumbled across this very topic by accident. When I picked up my vehicle from the dealer, it ran well enough. Then suddenly, right at the 500 mile mark (after what the manual calls a break-in period), the engine came to life and offered up a big boost in performance. Knowing nothing about this issue, I started a forum thread asking if Jeep put a governor on the vehicle to keep things for engine break-in during the first 500 miles. HA!

What I eventually figured out was that up until recently, I had been filling the vehicle with 87 octane gas. The last two times I tried 91 octane just for the hell of it. I completely forgot about it, and when I got a hell of a boost, I was wondering why! And you know why I got such a significant boost? These were sizzling hot 102 degree days. The very condition under which Jeep says the ncreased performance is most noticeable.

So hey, I agree with you the performance is not always going to be there. And if you look at the section I posted about the 3.6L engine, "higher octane premium gasoline will not provide any benefit [...] in these engines". It's not universal, it's situational (having a turbo, having hot temperatures, towing a vehicle). The temperatures have cooled off quite a bit (low 70s) but I still believe I'm seeing increased performance.

Earlier you asked for proof that premium runs better. Jeep says it won't do anything for your 3.6L engine, so I can understand why you don't see anything (despite compression ratios). Anyhow, come next summer, if you've got a metric for proof that you'd like to see, I'm game. Let me know and I'll give it a shot.

Now if you're asking for me to run a couple of dyno tests, I'm afraid that you're going to have to foot the bill for that one.

PS: I agree with you on the issue of engine life. The vehicle appears to adapt and remember it's adaptation to a tank of gas. Sure, there might be a small bit of initial knock for a very brief period before it adapts, but that's insignificant compared to years gone by where a vehicle would run in that state the entire time. Unless the engine was on the edge of being damaged, I don't see a short term knock harming anything.

 

[entropy]

The performance improvement from higher octane gas was significant enough that Jeep wrote about this very topic in the manual...

...but Jeep doesn't say by how much higher octane will increase performance, do they? Just that it does by some noticeable amount.

I stumbled across this very topic by accident. When I picked up my vehicle from the dealer, it ran well enough. Then suddenly, right at the 500 mile mark (after what the manual calls a break-in period), the engine came to life and offered up a big boost in performance. Knowing nothing about this issue, I started a forum thread asking if Jeep put a governor of the vehicle to keep things mild for the first 500 miles. HA!

What I eventually figured out was that up until recently, I had been filling the vehicle with 87 octane gas. The last two times I tried 91 octane just for the hell of it. I completely forgot about it, and when I got a hell of a boost, I was wondering why! And you know why I got such a significant boost? These were sizzling hot 102 degree days. The very condition under which Jeep says we'll see increased performance.

So hey, I agree with you the performance is not always going to be there. (And if you read the section I posted about the 3.6L engine, "higher octane premium gasoline will not provide any benefit [...] in these engines." It's situational (having a turbo, having hot temperatures, towing a vehicle). The temperatures have cooled off quite a bit (low 70s) but I still believe I'm seeing increased performance.

Earlier you asked for proof that premium runs better. Jeep says it won't do anything for your 3.6L engine, so I can understand why you don't see anything (despite compression ratios). Anyhow, come next summer, if you've got a metric for proof that you'd like to see, I'm game. Let me know and I'll give it a shot.

Now if you're asking for me to run a couple of dyno tests, I'm afraid that you're going to have to foot the bill for that one.

My answer was to someone asking about the 3.6 V6. Jeep has never hinted at the use of higher than 87 for the 3.6 V6. I don't really care much about the 2.0 Turbo because I didn't buy that. But I am always curious about random shit, just for the sake of it, and so I came here.... But I am not willing to pay for something that wont change my life at all lol.

 

[jmccorm]

My answer was to someone asking about the 3.6 V6. Jeep has never hinted at the use of higher than 87 for the 3.6 V6. I don't really care much about the 2.0 Turbo because I didn't buy that. But I am always curious about random shit, just for the sake of it, and so I came here.... But I am not willing to pay for something that wont change my life at all lol.

You're quick to the draw! I edited my message just a little too late. I agree with you on brief engine knock and the life of the engine. I don't see it having an impact. I am led to believe that, in general, the higher octane fuels also have higher amounts of detergent added to them.

So you and I agree on octane on the 3.6 (and knock and engine life), what are your thoughts on the increased additives added with higher octane fuel and their impact on engine life?

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