Do we have to run premium?

[tts42572]

Now that's an excellent repsonse.

I spoke to a service manager at a large dealership on this issue and he essentially said the same exact things. He told me he runs premium in his Turbo Jeep. Basically said if you only plan to have the Jeep for a few years, run 87 and don't worry about it. But if it's a vehicle you plan to own long term, treat it right with premium you're likely to reap the benefits down the road.

I'll be running premium in my 2.0T.

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

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[Bruce Willys]

Octane has NOTHING to do with power. Please stop spreading this fallacy around.

That’s not true. Once the ECU detects knock, it will revert to a lower power map and pull timing. Whether most consumers would notice or even be able to tell the difference at all is another matter. There’s a reason FCA recommends premium in hot weather and under high load (towing) with the turbo, the engine is more likely to knock in those scenarios if running lower octane fuels —-> pull timing ——> less power.

 

[chevymitchell]

That’s not true. Once the ECU detects knock, it will revert to a lower power map and pull timing. Whether most consumers would notice or even be able to tell the difference at all is another matter. There’s a reason FCA recommends premium in hot weather and under high load (towing) with the turbo, the engine is more likely to knock in those scenarios if running lower octane fuels —-> pull timing ——> less power.

Yes. It is true.

Pulling timing once detecting knock is an ECU function as you have stated.

Nothing to do with Octane ratings of the fuel. The energy in the fuel does not change from 87-91-93.

This has been beat to death for decades.

Here's one of dozens of videos available for some learnin'. :

 

[Bruce Willys]

Yes. It is true.

Pulling timing once detecting knock is an ECU function as you have stated.

Nothing to do with Octane ratings of the fuel. The energy in the fuel does not change from 87-91-93.

This has been beat to death for decades.

Here's one of dozens of videos available for some learnin'. :

When the ECU pulls timing, it reverts to a fuel map that makes less peak power like you said, you’re agreeing with me if you understand what less ignition timing does. I’ve tuned multiple turbo engines over the years, I’ve personally seen the difference between the different fuel tables on multiple platforms and the effects of heat and lower octane fuels on fuel strategies/timing.

When did I say anything about less energy? If the ECU pulls timing, the engine makes less power. The ECU will pull timing running regular under the conditions I mentioned (and the conditions that FCA mentions in the owners manual). Again, whether it’s a noticeable amount depends on the user and operating conditions.

 

[chevymitchell]

When the ECU pulls timing, it reverts to a fuel map that makes less peak power like you said, you’re agreeing with me if you understand what less ignition timing does. I’ve tuned multiple turbo engines over the years, I’ve personally seen the difference between the different fuel tables on multiple platforms and the effects of heat and lower octane fuels on fuel strategies/timing.

When did I say anything about less energy? If the ECU pulls timing, the engine makes less power. The ECU will pull timing running regular under the conditions I mentioned (and the conditions that FCA mentions in the owners manual). Again, whether it’s a noticeable amount depends on the user and operating conditions.

...and when did I say anything about timing?

 

[chevymitchell]

When the ECU pulls timing, it reverts to a fuel map that makes less peak power like you said, you’re agreeing with me if you understand what less ignition timing does. I’ve tuned multiple turbo engines over the years, I’ve personally seen the difference between the different fuel tables on multiple platforms and the effects of heat and lower octane fuels on fuel strategies/timing.

When did I say anything about less energy? If the ECU pulls timing, the engine makes less power. The ECU will pull timing running regular under the conditions I mentioned (and the conditions that FCA mentions in the owners manual). Again, whether it’s a noticeable amount depends on the user and operating conditions.

No need to post anymore about it. Run 87 in your 2.0T if you want until you need to pull something. I run 93 all the time because the net weight gain from a long arm with 37's and all my camping stuff is like pulling a trailer all the time.

 

[jeepoch]

Yes. It is true.

Pulling timing once detecting knock is an ECU function as you have stated.

Nothing to do with Octane ratings of the fuel. The energy in the fuel does not change from 87-91-93.

Shawn and others referring to the octane value as not the fuel's energy rating is correct. Gasoline as refined for the standard American market all have the same energy content per volume independent of it's octane rating. They all have the same amount of energy.

It's only the CONSISTENCY of the flash-point of the fuel which is specified by it's octane rating.

All power perception is indeed a function of the engine controller unit (ECU), not the fuel. If there is a noticeable difference, it is due to how the controller is 'reacting' or adapting to it's current dynamic operating conditions. Some ECU's and it's hardware/software are certainly better than others. High performance muscle cars will have more refined designs than that of a lower cost economy vehicle. I'm pretty confident that our JL's are somewhere middle of the road in terms of controller sophistication.

For reference and full disclosure, about 50% of all the software features that I had worked with had very specific torque constraints to limit power output in order to prevent transmission and powertrain damage. The ECU developers and calibrators always had to walk that very fine line of power perception and equipment protection.

Furthermore, the obvious exception for fuel energy ratings are variants such as E85, percentage of ethenol content, seasonal additives, or even contaminants such as water in the fuel. Typically however, the fuel sold at any pump, offering different octane options, all have the exact same energy content per volume.

One last piece of advice, never fill up at a station when the tanker truck is there. NEVER, not even in haste. Either go somewhere else or wait a while (perhaps a half hour or so). When filling the underground tanks, sediment does seep into the holding tank over time. The adding of new product stirs whatever sediment has accumulated around. It takes time for it to settle again to the bottom of the tank. You certainly want to keep it there rather than inadvertently bringing it into your vehicle's tank. There are of course filters that minimize the larger particulates but anything that seeps through has a chance to clog an injector or even worse making into your piston. It doesn't take much abrasion on the rings or walls to degrade compression.

So please be cognizant of not only the octane content but also the quality of the fuel as well.

Jay

 

[Bruce Willys]

...and when did I say anything about timing?

You said:

Octane has NOTHING to do with power. Please stop spreading this fallacy around.

I wrote why that’s not correct, lower octane fuel will cause the ECU to pull timing and run a lower power map. Nothing personal, I disagree with some of what you wrote and said why. That’s how a forum works, reply if you disagree with anything that I said and set the record straight.

 

[chevymitchell]

You said:



I wrote why that’s not correct, lower octane fuel will cause the ECU to pull timing and run a lower power map. Nothing personal, I disagree with some of what you wrote and said why. That’s how a forum works, reply if you disagree with anything that I said and set the record straight.

Alright, man. This is the last reply I'll give you on this topic. Please do your homework.

My point is: Octane has nothing to do with power.

You can run 87 - 91- 93 - 105; it doesn't matter. They will all produce the same or marginally the same power.

In order for the octane to come into play for power, other things must be changed. You must change those "other" things in order to make more power. The octane of the fuel is not what is making the power. The advanced timing is. The higher boost pressure is. The air density is. The cooler air is. NOT the octane rating of the fuel. Having a higher octane rating just allows you to advance timing. I understand what you're saying. I've been doing this a long time, as well. There is no power increase unless you change timing. Octane doesn't matter without timing.



You will not feel a difference unless something else changes. Even then, most timing algorithms are written to cut the advanced timing short. This is why people that run 93 in their corollas (generally speaking) end up with plugged catalytic converters at 100k miles. The knock sensor input and the ECU will not allow for endless timing advance. It will cut it short unless you have a tunable ECU and a map created outside the factory tune, which are likely dialed way back to keep from breaking things to begin with.

 

[Bruce Willys]

Alright, man. This is the last reply I'll give you on this topic. Please do your homework.

My point is: Octane has nothing to do with power.

You can run 87 - 91- 93 - 105; it doesn't matter. They will all produce the same or marginally the same power.

In order for the octane to come into play for power, other things must be changed. You must change those "other" things in order to make more power. The octane of the fuel is not what is making the power. The advanced timing is. The higher boost pressure is. The air density is. The cooler air is. NOT the octane rating of the fuel. Having a higher octane rating just allows you to advance timing. I understand what you're saying. I've been doing this a long time, as well. There is no power increase unless you change timing. Octane doesn't matter without timing.



You will not feel a difference unless something else changes. Even then, most timing algorithms are written to cut the advanced timing short. This is why people that run 93 in their corollas (generally speaking) end up with plugged catalytic converters at 100k miles. The knock sensor input and the ECU will not allow for endless timing advance. It will cut it short unless you have a tunable ECU and a map created outside the factory tune, which are likely dialed way back to keep from breaking things to begin with.

You tell me to do my homework, yet nothing I said was incorrect and it comes from first hand experience. You don’t seem to understand that the engine isn’t running at optimal efficiency on low octane fuel when the ECU starts pulling timing. The engine produces less power on low octane fuel under high load conditions and high heat conditions to protect itself. There is a benefit to running premium fuel depending on operating conditions which is why the engineers recommend it.

Stay true to your word and make that last post your last reply to this, you’re giving people bad info on the subject. The engineers knew what happens with low octane gas which is why they recommend premium under those conditions.

 

[kapk22]

Alright, man. This is the last reply I'll give you on this topic. Please do your homework.

My point is: Octane has nothing to do with power.

You can run 87 - 91- 93 - 105; it doesn't matter. They will all produce the same or marginally the same power.

In order for the octane to come into play for power, other things must be changed. You must change those "other" things in order to make more power. The octane of the fuel is not what is making the power. The advanced timing is. The higher boost pressure is. The air density is. The cooler air is. NOT the octane rating of the fuel. Having a higher octane rating just allows you to advance timing. I understand what you're saying. I've been doing this a long time, as well. There is no power increase unless you change timing. Octane doesn't matter without timing.



You will not feel a difference unless something else changes. Even then, most timing algorithms are written to cut the advanced timing short. This is why people that run 93 in their corollas (generally speaking) end up with plugged catalytic converters at 100k miles. The knock sensor input and the ECU will not allow for endless timing advance. It will cut it short unless you have a tunable ECU and a map created outside the factory tune, which are likely dialed way back to keep from breaking things to begin with.

You tell me to do my homework, yet nothing I said was incorrect and it comes from first hand experience. You don’t seem to understand that the engine isn’t running at optimal efficiency on low octane fuel when the ECU starts pulling timing. The engine produces less power on low octane fuel under high load conditions and high heat conditions to protect itself. There is a benefit to running premium fuel depending on operating conditions which is why the engineers recommend it.

Stay true to your word and make that last post your last reply to this, you’re giving people bad info on the subject. The engineers knew what happens with low octane gas which is why they recommend premium under those conditions.

This has gotten interesting.

 

[YellOhJL]

I think this is what is missing:

Will the average car gain power by putting in a higher octane gasoline? No. If the car is made to run on 87 and it does not knock with 87, you are just wasting money.

Will a car that is design to run on a range on octane gain power with a higher octane? Yes, if it is designed to increase performance parameters when higher octane is used. Is it gaining power because 91/93 has more energy; no. It is running a tune that produces more power that would cause pre-ignition (knock) if 87 octane was run.

 

[Zandcwhite]

Octane has NOTHING to do with power. Please stop spreading this fallacy around.

Octane has everything to do with allowable timing advance without Pre-detonation, especially in boosted applications. Explain why Mazda literally rates their engine at 23 more horsepower on premium fuel? An ecu capable of further advancing timing with the added octane does indeed make more power. Older fuel injection systems didn’t take advantage of that fact, but clearly Mazda does. Jeep recommending the higher octane for peak performance would make one think they do too. Guess what the difference between canned 87 octane and 93 octane tunes is...timing. With that timing and added knock resistance, those tunes make more power. Adding octane to the same tune won’t do anything, so you are sort of correct.

 

[chevymitchell]

Octane has everything to do with allowable timing advance without Pre-detonation, especially in boosted applications. Explain why Mazda literally rates their engine at 23 more horsepower on premium fuel? An ecu capable of further advancing timing with the added octane does indeed make more power. Older fuel injection systems didn’t take advantage of that fact, but clearly Mazda does. Jeep recommending the higher octane for peak performance would make one think they do too. Guess what the difference between canned 87 octane and 93 octane tunes is...timing. With that timing and added knock resistance, those tunes make more power. Adding octane to the same tune won’t do anything, so you are sort of correct.

Lol. You guys are awesome. These are all great points. Good beer convo, for sure.

Look at it this way. Higher octane rated fuel gives the vehicle "permission" to adjust timing. (Timing adds power, not the fuel.) By permission, I mean adjust timing without knock or damage.

You cannot take an old small block and go from 87 to 93 and make power. Higher octane does not have anything to do with making power. (It's a prerequisite to making power.) This is my point. You must adjust timing and before you do, the prerequisite of having the right fuel has to be there. A lot of old school guys timed their cars based on knock. If you didn't have a timing light, you turned the timing back until it knocked, then advanced from there.

Any modern car automatically adjusts timing based on sensor inputs. It's what Honda does with their VTEC. (Variable TIMING electronic control) VTEC is controlled by oil pressure allowing more air in, not just by the ECU adjusting timing. There is a very similar system on the Mazda and many, many others. Again, nothing to do with octane. The higher octane isn't creating the power, the timing is.

We're all arguing the same points, really, but you don't have an argument without timing. Remove timing and my point stands. Higher octane is just a prerequisite to adding power. Your last sentence says exactly what my point is.

I ran a mix of 93/110 purple in my Camaro. When I went to straight 110 (no mix), If I didn't adjust timing, there was no bump in power.

When you're at the strip and you have your laptop plugged into your FAST ECU and you want to add power... you're not adding higher octane fuel. Only adding and taking away timing. We all agree on the same things. My only point is that: Octane has nothing to do with power. It's a prerequisite.

Thanks for the entertaining conversation. This has been fun. I love Gearheads. Lol. We're all the same.

Bonus article from Amsoil: https://www.amsoil.com/newsstand/articles/high-octane-gas-boost-performance/

"...nothing to do with energy content..."

 

[srt20]

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!

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