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Discussion Starter #1
So, is there any advantage to using greater than 87 octane on the LGX 3.6 motor? The owner's manual just says use 87 octane or higher. I have a 2016 3.6 Performance Coupe.

I'm wondering if there is any documented performance improvement when using premium fuel, i.e. will the LGX 3.6 respond and allow for an increase in timing advancement, injector pulse width, etc.?

My prior training in the FCA world was that generally speaking a motor tuned for 87 won't respond to higher octane. In fact, using higher octane can actually be harmful and will lead to an increase in carbon deposits. Wondering if it's the same for GM?
 

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There are no less than 10 gas wars currently running in the forums for vehicles that use the 3.6 in its several iterations. Snoop around.
 

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No, there is no advantage, on that engine. Most all gasoline brands have the same additive package between 87 and 91/93 octanes except for shell and exxon/mobile, who are advertising their premiums with more additives.

If you got a tune from Trifecta, they specify that you'll only get the advetised gains if you use premium.
 

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Discussion Starter #4
Thanks for responding. There doesn't seem to be any octane consensus at all on any forum on the stock tune for the LGX. I'm keeping mine stock so I'll send pick with 87.
 

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Discussion Starter #5
There are no less than 10 gas wars currently running in the forums for vehicles that use the 3.6 in its several iterations. Snoop around.
I did look around and couldn't find any credible information beyond what is vaguely worded in the owners manual. There seems to be no consensus on the stock LGX beyond anecdotal speculation that using above 87 "might" be beneficial. I was hoping to hear from someone who had some technical expertise regarding the ECM's ability to make adjustments with higher than 87 octane and potential subsequent higher knock threshold.
 

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'93 SedanDeville 60 Special
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The answer is,
Your engine is telling you
It is not just the fuel but other factors also involved as to weather, elevation, drive style and gas brand (as what cleaners they use) so what gas may be good for one is engine makeup, not for another engine

Let your engine tell you, listen to it
If using 87 octane and you hear no engine knock then all is fine, and paying for higher octane gets no gains

IF engine is reporting knock then raise the octane level
Reason is, the PCM is getting information, if knock sensors report active knock then PCM will react and start pulling timing
The more knock and longer there is knock the PCM pulls even more timing to a point PCM feels the quality of gas is not great and switches to a low octane timing table and stay there until at least 25% more fuel is added to gas tank and then switches back to the high octane timing table being used.

Really what octane amount is for is to fight off knock.

Also the amount of engine compression for a engine design is, the higher it is the more apt there will be knock
so a higher octane is required.

In short if no knock use lower grade, if knocking and want NOT to lose performance
(by lower timing = less torque, means less HP)

DO not let lack of maintenance induce more knock by keeping the cylinders and valves clean with gas with good cleaners but also keep internals clean with a good decarb product like SeaFoam
The more carbon buildup layer in cylinders then increases the compression which increases knock.

Before upping octane level make sure that carbon buildup is not the real cause and just masking the problem by upping the octane level and do not forget heat, may be able to use 87 octane in winter but in summer or racing heat needs higher octane and lastly crap Ethanol, reason some states require a summer fuel sold and another for cold months. E10 gas can cause engine to run even leaner (by about 7% more) causing hotter charge to cylinders and induces more knock. Add summer heat and it is worse

For us performance types we go further by using only non Ethanol type fuel (allows for lower octane level) and added water/methanol injection kits to assure internals are kept clean, cools the cylinder charge and also that ups the octane level

Now getting a tune in PCM for performance and it is set to run higher timing then what stock was, that will cause more knock and hence a higher octane is required.
 

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Discussion Starter #7
The answer is,
Your engine is telling you
It is not just the fuel but other factors also involved as to weather, elevation, drive style and gas brand (as what cleaners they use) so what gas may be good for one is engine makeup, not for another engine

Let your engine tell you, listen to it
If using 87 octane and you hear no engine knock then all is fine, and paying for higher octane gets no gains

IF engine is reporting knock then raise the octane level
Reason is, the PCM is getting information, if knock sensors report active knock then PCM will react and start pulling timing
The more knock and longer there is knock the PCM pulls even more timing to a point PCM feels the quality of gas is not great and switches to a low octane timing table and stay there until at least 25% more fuel is added to gas tank and then switches back to the high octane timing table being used.

Really what octane amount is for is to fight off knock.

Also the amount of engine compression for a engine design is, the higher it is the more apt there will be knock
so a higher octane is required.

In short if no knock use lower grade, if knocking and want NOT to lose performance
(by lower timing = less torque, means less HP)

DO not let lack of maintenance induce more knock by keeping the cylinders and valves clean with gas with good cleaners but also keep internals clean with a good decarb product like SeaFoam
The more carbon buildup layer in cylinders then increases the compression which increases knock.

Before upping octane level make sure that carbon buildup is not the real cause and just masking the problem by upping the octane level and do not forget heat, may be able to use 87 octane in winter but in summer or racing heat needs higher octane and lastly crap Ethanol, reason some states require a summer fuel sold and another for cold months. E10 gas can cause engine to run even leaner (by about 7% more) causing hotter charge to cylinders and induces more knock. Add summer heat and it is worse

For us performance types we go further by using only non Ethanol type fuel (allows for lower octane level) and added water/methanol injection kits to assure internals are kept clean, cools the cylinder charge and also that ups the octane level

Now getting a tune in PCM for performance and it is set to run higher timing then what stock was, that will cause more knock and hence a higher octane is required.
thanks
 

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I dont have experienced with the lgx, however with the lfx I do notice a difference between 87 and 93 octane. On 87 octane I regularly see knock retard upwards of 7 degrees and with 93 I rarely ever see any knock retard.
 

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Discussion Starter #10
I dont have experienced with the lgx, however with the lfx I do notice a difference between 87 and 93 octane. On 87 octane I regularly see knock retard upwards of 7 degrees and with 93 I rarely ever see any knock retard.
Thank you. Interesting to hear some thing factual. I'll do some experimenting on the LGX to see if my seat dyno can feel any improvement on 93. Appreciate your response!
 

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2013 3.6 RWD Premium - 2006 BMW Z4M
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Here's information on the LFX but I have never seen something similar for the LGX - https://www.cadillacforums.com/threads/3-6-ats-testers-needed-for-tune-development-at-diablosport.616921/page-2

Originally had 89 octane in the car -
"So, for those who enjoy running less than premium fuel (I don't even want to imagine what 87 would have been like), this car was pulling 9° of timing right away and wasn't even worth making a full pull. Knock city.
If you are running 87 in a 3.6 ATS/CTS, I'd guess you are missing out on an easy 10-15 rwhp and a good amount of torque. "
"OK, on 93 the car picked up about 12 rwhp and 15-17 ft/lbs for a big range. Believe it or not, it was still knocking on 93, the stock cal leaves much to be desired. It needed to be fixed to find power, rather than the traditional means. "
 

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Discussion Starter #12
Thank you! Very interesting to see some real data. I wonder what the chances are the fuel mapping strategy is the same on the LGX? Somewhat likely, I would assume. I'm looking forward to doing some octane experimenting. I'm guessing someone will eventually do a deep dive on the LGX and we'll know for sure.
 

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Here is part of 3 stock GM calibration tables for a 2016 LFX V6 engine within the PCM

As seen looking (tables below) at what the timing values the PCM will command as to what RPMs and per how much air/fuel in cylinders
If after adding fuel to the gas tank, PCM using the HIGH octane timing table.
If no knock then those higher values are used as seen below

IF there is knock then PCM looks at the values of low octane timing table and begins to start lowering the timing values from what high table values are and PCM can yank as much as 8 deg at a time

As more knock occurs then PCM pulls even more timing until if knock happens multi times in a row drops down to the low timing table values
As I have mentioned IF PCM drops into low table it then will continue to only use that table values until at least 25% more fuel is added to gas tank and that resets PCM to go back to using HIGH octane timing values

No, knock, using 87 octane gas then no gain go to higher octane fuel
Unless you come to someone like I do and raises the timing tables, engine gets a performance gain
BUT now must only use higher octane gas

576151
 

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2019 XTS Luxury AWD, 2004 SRX N* AWD (gone)
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:confused: Team ZR-1. Would you please explain in layman terms. Is 87 okay or should high octane be used for the LFX. Pros and cons of each. Tx!
 

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How is this ?

1. Look at gas cap or owners manual, in cases like my 1993 4.9 liter Deville it says uses premium fuel, so does my 1999 Corvette. Has higher engine compression so needs higher octane.

2. If using 87 and for most of your drive style you hear no engine ping/knock then stay with 87, no performance gains using higher octane in this case

3. If though in hot weather months hear ping then for those months using higher octane, will prevent losing performance due to PCM (Powertrain Control Module) yanking timing out. Go back to winter grade in colder months.

4. Quality of cleaners in gas, good idea maybe like every month or for 1 tank is change brands of gas station because if using the same brand all the time then only using the cleaners they have in gas and by switching to another brand it may have different type of cleaners other brand did not.

5. CHECK the gas pump for a label that must state how much Ethanol percent it has. Best use E10 gas, E15 will make the AFR leaner and cause more ping. If not labeled ask station what you would be pumping in

6. If you decide to use E15, then must use a higher octane level to reduce ping and loss of timing/torque

7. Do not judge quickly judge gas pumped in as time for that fuel to reach engine and the PCM then takes time to re-learn maybe 30 miles or so using different drive styles

8. Using higher octane at higher costs when engine is not knocking is waste of money and no performance gains

9. If engine pings using 87 octane the negative is lots of ping/knock means pistons/rings bouncing against cylinder walls, not good long term and the PCM operating within the low octane timing table is loss of performance

10. by using a good de-carb product (like SeaFoam) couple times a year will keep the valves and cylinders clean which would help limit ping and octane level needed

Being you can get OBD-II scanners for like $60-70 that work off your cellphone and is easy to use, get one because you can easily see if there is knock and by how much would allow you to make the right decision to use 87 or move up to another grade.
Could have a OBD-II knock meter/gauge seen on cellphone that is set for ping/knock and then a simple glance will tell you what your engine needs to your drive-style or weather.
 

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To Explain about percentage of Ethanol and octane level
The more Ethanol is in the gas the leaner the AFR (Air Fuel Ratio) will be and that induces more engine ping

GM has a table I show below that PCM is using some sensor to determine how much Ethanol is in fuel and from that commanding what the AFR will be for most engine modes.

As seen below if using straight gas, no Ethanol then PCM commands the AFR to be about 14.7:1
(14.7 parts of air to 1 part of gas ratio)
But if it senses % of Ethanol is E10, being it burns leaner and causes ping then PCM is forcing the AFR richer to like
14.3:1 and if E15 then about 13.9:1

So as to octane, if the Ethanol gas brand used causes engine to run leaner which causes more ping then up the octane level of gas being used.

576162
 

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Thanks for the reply. My XTS Luxury calls for high tier 87 (or better). In Canada 87 has up to 10% E. Shell V has no E, but cost is a lot more than 87. Because the engine compensates for ping, I doubt if it would be heard by most imo. I have a maxdiag Elite. It lists the spark retard, but I really don't understand it, that is, what is a bad amount vs good amount on different fuel Octanes. I try to switch gas - mobil or Esso, Shell from one fill to another, but it doesn't always happen. From what I've read a fuel additive doesn't do much good for direct injection such as the LFX. I just want to use a good octane for my engine but not pay for a higher octane if not needed.
 

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Look at the 2 OBD-II results below from 1 car, as how it performed stock tune and 87 octane
Look at the left side for the scales and then follow at the same time as to what RPMs, amount of knock and what the timing is

Then look at the lower results of same car after I tuned the PCM and used 92 octane E10 gas
As you see in the before results when doing WOT there was as much as 16 deg of timing yanked due to knock and then notice how the timing drops and what the torque was

Compare that with the after results and notice knock even at 6,000 RPMs is only pulling 3 degrees and how stable the timing is holding
End results is look at what the torque is before and then after
Notice the width (time it took) for start to end of knock before and then how narrow the time is for after as it now reacts quicker to recover from that knock

PCM is either going to control by low timing GM put in stock calibration or a after effect of yanking timing after knock occurs but the PCM is not to be perfect for best performance, its task it to limit warranty issues and passing smog testing and reacts slowly as the co-processor it uses if fairly slow

Add other factors such as heat, weather, elevation and that will also effect amount of knock and what effects PCM does to try and recover quickly from the effects of ping

In the end the results show WHEN a engine knocks the ill effects to performance but how to limit that with better fuel
and then tune to add more timing and better what the AFR is to assure good cylinder charge for best performance

Tuning changes then can up the torque and HP while reducing the chances of ping's ill effects to timing
Gains doing this only by PCM tuning can be 30-40 flywheel HP and low to mid range RPMS faster and higher torque output

Totally stock with 87 Octane gas :

576168



After changes made and better gas :

576167
 

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Thanks for your time, and Happy New Year to you in one hour 6 min (my time here). Okay, I think I see what you mean ..the less spark retard the better which depends on gas/tune if I have understood correctly. My XTS is stock, no tune, so would 87 be fine and not pay for higher octane gas or should I use higher octane without E...which will give me the least knock/timing retard and hence performance ie. run best in your estimate? I guess it may be differ according to season - summer vs winter? I could connect my scanner and see which fuel has the least retard/knock after a couple of fill ups with higher octane, but as mentioned, in your estimate which would you recommend for this engine?
 

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Discussion Starter #20
Here is part of 3 stock GM calibration tables for a 2016 LFX V6 engine within the PCM

As seen looking (tables below) at what the timing values the PCM will command as to what RPMs and per how much air/fuel in cylinders
If after adding fuel to the gas tank, PCM using the HIGH octane timing table.
If no knock then those higher values are used as seen below

IF there is knock then PCM looks at the values of low octane timing table and begins to start lowering the timing values from what high table values are and PCM can yank as much as 8 deg at a time

As more knock occurs then PCM pulls even more timing until if knock happens multi times in a row drops down to the low timing table values
As I have mentioned IF PCM drops into low table it then will continue to only use that table values until at least 25% more fuel is added to gas tank and that resets PCM to go back to using HIGH octane timing values

No, knock, using 87 octane gas then no gain go to higher octane fuel
Unless you come to someone like I do and raises the timing tables, engine gets a performance gain
BUT now must only use higher octane gas

View attachment 576151
Here is part of 3 stock GM calibration tables for a 2016 LFX V6 engine within the PCM

As seen looking (tables below) at what the timing values the PCM will command as to what RPMs and per how much air/fuel in cylinders
If after adding fuel to the gas tank, PCM using the HIGH octane timing table.
If no knock then those higher values are used as seen below

IF there is knock then PCM looks at the values of low octane timing table and begins to start lowering the timing values from what high table values are and PCM can yank as much as 8 deg at a time

As more knock occurs then PCM pulls even more timing until if knock happens multi times in a row drops down to the low timing table values
As I have mentioned IF PCM drops into low table it then will continue to only use that table values until at least 25% more fuel is added to gas tank and that resets PCM to go back to using HIGH octane timing values

No, knock, using 87 octane gas then no gain go to higher octane fuel
Unless you come to someone like I do and raises the timing tables, engine gets a performance gain
BUT now must only use higher octane gas

View attachment 576151
Thanks for the detailed response. Very interesting stuff.
 
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