Data logging regular vs. premium

[PandaBear]

Here's the bigger question: is knock detection always turned on, or only under circumstances where the OEM feels detonation is most likely to affect intended engine durability?

Things like these are always on a "normal" distribution, aka a bell curve. There will be statistically more pings on 87 vs 91 for the same timing and compression, that's a fact. The amount of retardation an ECU can do would be tuned to either make it safe enough, but reduces mpg, or they cannot do enough detuning and the extra ping would eat into the safety margin, leading to shorter life. This would definitely be internal data and not published outside.

 

[AZjeff]

Wow, you have cheap 91 E0. Here in PA, 90 E0 is $1+ more than E10 87 or E15 88.

You realize Herman's is almost 2 years old? Before you resurrected this thread the last post was in Oct 22. It was interesting then and still is.

 

[umungus1122]

You realize Herman's is almost 2 years old? Before you resurrected this thread the last post was in Oct 22. It was interesting then and still is.

Yes it is interesting. Prices here have not changed significantly in 2 years. E15 88 is $3.04 currently, while 90 E0 is $4.19. Same basic variation as 2 years ago.

 

[tvaughn]

Do I fill up with premium?
Opinion incoming: Yes. It's pretty obvious that the ECM doesn't have to intervene as much because knock is simply less present. Yeah, the extra cost stinks, especially when getting 9.5mpg while towing. For me, the better driveability is worth the extra cost. Much of the benefit for me comes down to the shift characteristics. GM's 8-speed isn't the most refined or sophisticated transmission. I'd go so far to say that the shifting is often mushy. What does that have to do with the fuel in the tank? It's all about timing control. GM's torque reduction strategy largely centers around retarding timing during a shift to reduce input torque while the shift is completed. I feel that the premium fuel allows much more stable timing control when the ECM is retarding and advancing during shifts. It makes the whole shift feel better because the ECM can begin advancing timing more aggressively after the shift, leaving the throttle feeling crisper when exiting the shift and less mushy. Same thing with regular throttle tip-in and during auto-stop restarts: Most stable timing control.

I appreciate you looking at this more holistically. For the same reason, I continue to run 91 on my GX460 (which is required) even though the same engine was quoted for 87 in the 4.6 Sequoia/Tundra. This can be a point of contention on the forums, especially since the Sequoia/Tundra were rated at an ever-so-slightly higher peak horsepower- they don't have full-time 4WD on that note like the GX.

But most people don't consider the under-curve power and drivability, something Lexus would be allowed to focus more on compared to the 4.6 Sequoia/Tundra, which had to be competitive in its field by allowing 87 octane. Not to mention in CA, 91 is usually only about $.30 more per gallon, as evident by one the least expensive stations near me.

 

[Pew]

How does it drive if you dump in a gallon of xylene or toluene to boost the octane to around 95? Adding some higher ethanol content E85 to raise it to 95-96 octane?

I've never done it before nor personally know anybody that has put in xylene or toluene but a few of us have put in a gal or two of 100oct with the rest being 93oct on track days to help against any knock. However, we were specifically tuned for 93oct so any benefits from higher oct fuel was purely for knock resistance.

There were a few individuals that 'blended' their own E85 or mixed ethanol before E85 became prevalent. For the evo the issue is getting the perfect percentage (because you would need a specific tune set for that oct level, pre-flex fuel) and you needed upgraded injectors and fuel pump for E85, even on a stock setup.

 

[KrisZ]

Here's the bigger question: is knock detection always turned on, or only under circumstances where the OEM feels detonation is most likely to affect intended engine durability?

I would argue that if OEMs determined that certain amount of knock will not cause damage, and it would be based on a lot of testing, not their feelings, then it goes back to the same question, does it really matter?

Drivability argument is really the only one we can settle on when it comes to this IMO. Engine damage? It’s all theoretical talk as we do not see failures like that.

 

[Jetronic]

Always lots of chatter about regular fuel versus premium and whether it makes a difference. The consensus usually lands somewhere between, "If the manufacturer doesn't recommend it, you're wasting your money," and "Modern engines have knocks sensors and will adjust timing accordingly, so you won't hurt anything." A link to Consumer Reports or Edmunds is usually thrown in there sometime too.

I decided to data log knock retard and get receipts.

The setup for this is my 2020 Chevrolet Silverado, 5.3L V8, 8-speed trans, and ~23k miles. Notably, GM only recommends premium for the 6.2L, not the 5.3L. Both examples I'm sharing were logged while towing my 5,500 lb. travel trailer, so the truck was certainly doing some work. Both logs were taken on the same stretch of 55mph two-lane road in similar ambient conditions. In the screen shots, knock retard is the graph with the single red trace.

Regular
View attachment 123151

In the regular fuel log, you can see the saw-tooth knock retard pattern. The ECM responds to knock by retarding timing (~3-5 degrees in most instances), the knock abates, the ECM reduces the knock retard, the knock returns, the ECM adds knock retard, and so on.

Premium
View attachment 123152

Again, same road and similar ambient conditions. This trace is much different than the previous. Knock is largely absent with premium and what few blips do occur are easily corrected with minimal (~2 degrees) knock retard.

So, does premium fuel make a difference? In the case of my truck, absolutely. This is an engine that the manufacturer doesn't specifically recommend premium too. Imagine this same scenario in a 6.2L that does recommend premium: I certainly wouldn't expect it to be better.

Because I know the statements and questions are coming:

Why did you do this?
On a whim, I filled with premium. The driveability was so much better. Throttle tip-in was crisper, shifts were less mushy, fuel economy was better, and even restarts after an auto-stop were less jarring. I wanted to know what was going on.

The difference is because it was hot when you logged the regular!
Nope. Neither one was logged when it was hot. They were both logged in early fall, about two weeks apart. It was actually warmer when I logged the premium, which you can see in the increased engine oil and transmission fluid temp. Ambient temp and IAT is part of the standard channels that I log, I just don't graph them.

It's because you were towing! I don't tow, so this doesn't apply to me.
I have dozens of logs over the past 6 months, regular and premium, with and without the trailer. Regular consistently has more instances of knock retard on any given trip, no matter the situation. I chose these two to compare because I knew they were on exactly the same road and in a very similar operating envelope (ambient conditions and load). Comparing these two in particular shows a stark different between the two and also shows that even with premium, there still may be instances where knock retard will pull timing.

You had a bad tank of 87!
Not likely. See the part above about similar results over 6 months and multiple tanks of fuel. Both fuels were pumped from a very high-volume Costco, so they're Top Tier as well. This is the same station I fill up my wife's car at too. Never an issue with her vehicle.

From here, do with this what you will. I really don't care whether you use premium or regular and I'm not making a recommendation. I'm just sharing data where often only exists opinion.

Do I fill up with premium?
Opinion incoming: Yes. It's pretty obvious that the ECM doesn't have to intervene as much because knock is simply less present. Yeah, the extra cost stinks, especially when getting 9.5mpg while towing. For me, the better driveability is worth the extra cost. Much of the benefit for me comes down to the shift characteristics. GM's 8-speed isn't the most refined or sophisticated transmission. I'd go so far to say that the shifting is often mushy. What does that have to do with the fuel in the tank? It's all about timing control. GM's torque reduction strategy largely centers around retarding timing during a shift to reduce input torque while the shift is completed. I feel that the premium fuel allows much more stable timing control when the ECM is retarding and advancing during shifts. It makes the whole shift feel better because the ECM can begin advancing timing more aggressively after the shift, leaving the throttle feeling crisper when exiting the shift and less mushy. Same thing with regular throttle tip-in and during auto-stop restarts: Most stable timing control.

Did you log both external air temp and intake air temp? Is the intake air temp measured anywhere near the engine? Do you see an influence of air temp on the knock retard?

 

[The Critic]

I would argue that if OEMs determined that certain amount of knock will not cause damage, and it would be based on a lot of testing, not their feelings, then it goes back to the same question, does it really matter?

Drivability argument is really the only one we can settle on when it comes to this IMO. Engine damage? It’s all theoretical talk as we do not see failures like that.

I think the key here is, OEMs feel it will not cause any detriment when measured against their design lifespan.

For many BITOGers, OEM’s desired lifespan is different than what folks want. Hint: lifetime transmission fluid.

 

[burbguy82]

Always lots of chatter about regular fuel versus premium and whether it makes a difference. The consensus usually lands somewhere between, "If the manufacturer doesn't recommend it, you're wasting your money," and "Modern engines have knocks sensors and will adjust timing accordingly, so you won't hurt anything." A link to Consumer Reports or Edmunds is usually thrown in there sometime too.

I decided to data log knock retard and get receipts.

The setup for this is my 2020 Chevrolet Silverado, 5.3L V8, 8-speed trans, and ~23k miles. Notably, GM only recommends premium for the 6.2L, not the 5.3L. Both examples I'm sharing were logged while towing my 5,500 lb. travel trailer, so the truck was certainly doing some work. Both logs were taken on the same stretch of 55mph two-lane road in similar ambient conditions. In the screen shots, knock retard is the graph with the single red trace.

Regular
View attachment 123151

In the regular fuel log, you can see the saw-tooth knock retard pattern. The ECM responds to knock by retarding timing (~3-5 degrees in most instances), the knock abates, the ECM reduces the knock retard, the knock returns, the ECM adds knock retard, and so on.

Premium
View attachment 123152

Again, same road and similar ambient conditions. This trace is much different than the previous. Knock is largely absent with premium and what few blips do occur are easily corrected with minimal (~2 degrees) knock retard.

So, does premium fuel make a difference? In the case of my truck, absolutely. This is an engine that the manufacturer doesn't specifically recommend premium too. Imagine this same scenario in a 6.2L that does recommend premium: I certainly wouldn't expect it to be better.

Because I know the statements and questions are coming:

Why did you do this?
On a whim, I filled with premium. The driveability was so much better. Throttle tip-in was crisper, shifts were less mushy, fuel economy was better, and even restarts after an auto-stop were less jarring. I wanted to know what was going on.

The difference is because it was hot when you logged the regular!
Nope. Neither one was logged when it was hot. They were both logged in early fall, about two weeks apart. It was actually warmer when I logged the premium, which you can see in the increased engine oil and transmission fluid temp. Ambient temp and IAT is part of the standard channels that I log, I just don't graph them.

It's because you were towing! I don't tow, so this doesn't apply to me.
I have dozens of logs over the past 6 months, regular and premium, with and without the trailer. Regular consistently has more instances of knock retard on any given trip, no matter the situation. I chose these two to compare because I knew they were on exactly the same road and in a very similar operating envelope (ambient conditions and load). Comparing these two in particular shows a stark different between the two and also shows that even with premium, there still may be instances where knock retard will pull timing.

You had a bad tank of 87!
Not likely. See the part above about similar results over 6 months and multiple tanks of fuel. Both fuels were pumped from a very high-volume Costco, so they're Top Tier as well. This is the same station I fill up my wife's car at too. Never an issue with her vehicle.

From here, do with this what you will. I really don't care whether you use premium or regular and I'm not making a recommendation. I'm just sharing data where often only exists opinion.

Do I fill up with premium?
Opinion incoming: Yes. It's pretty obvious that the ECM doesn't have to intervene as much because knock is simply less present. Yeah, the extra cost stinks, especially when getting 9.5mpg while towing. For me, the better driveability is worth the extra cost. Much of the benefit for me comes down to the shift characteristics. GM's 8-speed isn't the most refined or sophisticated transmission. I'd go so far to say that the shifting is often mushy. What does that have to do with the fuel in the tank? It's all about timing control. GM's torque reduction strategy largely centers around retarding timing during a shift to reduce input torque while the shift is completed. I feel that the premium fuel allows much more stable timing control when the ECM is retarding and advancing during shifts. It makes the whole shift feel better because the ECM can begin advancing timing more aggressively after the shift, leaving the throttle feeling crisper when exiting the shift and less mushy. Same thing with regular throttle tip-in and during auto-stop restarts: Most stable timing control.

I may have missed it in your post, but how long did you drive after you changed the fuel? Was it long enough for the computer to learn?

 

[MrHorspwer]

I may have missed it in your post, but how long did you drive after you changed the fuel? Was it long enough for the computer to learn?

GM ECMs actually do a really neat trick when it comes to ignition timing and fuel octane (other OEMs may as well, I just have experience on the GM side).

When a significant change occurs in fuel level, indicating a large amount of higher or lower octane fuel may have been added to the tank, the ECM will briefly advance ignition timing to the point of detonation and make note of how much advance was required. This is used as a base indicator of how much timing advance the fuel will support and a roundabout way of the ECM knowing the fuels octane.

Early GM ECMs for LS engines (Gen III P01, P59, E40) actually used two completely different base maps for high and low octane fuel. Later Gen IV and V ECMs use a base offset on the timing for fuel quality.

This is all to say: The ECM adapts base timing really quickly after adding fuel.

These logs were taken a few weeks apart (two different camping weekends to the same campground). There was plenty of time for any learning to take place.

 

[350Rocket]

GM ECMs actually do a really neat trick when it comes to ignition timing and fuel octane (other OEMs may as well, I just have experience on the GM side).

When a significant change occurs in fuel level, indicating a large amount of higher or lower octane fuel may have been added to the tank, the ECM will briefly advance ignition timing to the point of detonation and make note of how much advance was required. This is used as a base indicator of how much timing advance the fuel will support and a roundabout way of the ECM knowing the fuels octane.

Early GM ECMs for LS engines (Gen III P01, P59, E40) actually used two completely different base maps for high and low octane fuel. Later Gen IV and V ECMs use a base offset on the timing for fuel quality.

This is all to say: The ECM adapts base timing really quickly after adding fuel.

These logs were taken a few weeks apart (two different camping weekends to the same campground). There was plenty of time for any learning to take place.

Would this have anything to do with how my fuel trims go from slightly lean (+9-+15%) to 0 or minus 5% for a fuel minutes after a refuel?

I'll have to watch the timing.

 

[WobblyElvis]

Modern engines have the ability to vary throttle angle, valve timing, intake plenum geometry, ignition timing and perhaps more. The mechanical compression ratio of the engine does not determine the max pressure in the combustion chamber all on it's own. Focusing on ignition timing is not seeing the whole picture. I have a 4 cylinder 2011 manual car with cable controlled throttle body. I can totally floor the throttle at 30mph is 5th gear and the engine does not hiccup at all. I wouldn't worry and detonation/ping damaging a new computer controlled engine.

 

[TiGeo]

I log a few of my cars regularly. Here is my '18 Atlas with the 3.6 VR6. This engine in prior models would call for premium fuel but now is shown for 87. I've posted details of this around here before so seraching it should be simple with my username but here you go. Variable control the extent I could. Similar temps. Same station (Costco). Both winter blend. Same WOT 2-3 gear pull on the same road. Clearly more KR with 87 than 93 but even that 93 has quite a bit which jives with what I see in my Sportwagen that winter blends ignite easier/cause more KR. What does this tell me? I run 87 but would run 93 if I was towing to gain a bit of power. I see zero difference in mpgs in normal driving that anyone could attribute to running 87 or 93 that could ever justify the cost difference per gallon. Final comment, this does represent audible pinging which is VERY rare in a modern vehicle, the knock sensors are very sensitive and effectively are preemptively retarding timing when they sense even the most minimum irregular ignition. If you hear audible knock, you have issues. There is nothing unsafe about either of these logs.

 

[wpod]

My Ford P/U with the 2.7 has a noticeable difference in power when at wot and running 91 octane gas when running 91 octane premium. I like to do Italian tune ups weekly cause Italian is in my genetics.