I believe you are correct. I did check the code with HP tuners on my Camaro and it was a lean bank. That car is tuned obviously. I just stay out of it for a bit and after a couple cycles the CEL goes away. Thats for both cars but never checked the C8. I do have a flex fuel kit on the Camaro but when I had the blower done I wasnt aware of the short falls with LT1 fueling and didnt touch it. If I knew then what I know now, I would of did a LT4 HPFP and injectors before putting the blower on. With my C7 thats exactly what I did during the build and even added a DSX sux pump for the hell of it. Shooting for 900ish HP on that build.

 

Not the LT2 I realize, but a lower hp 10.2:1 port injection NA V8 that was “tuned” for 89 octane though can run on 87. 93 is clearly overkill though it still made a noticeable amount more power than 87, which I think is similar to what you’d see with an LT2 on 94 vs 91. Not sure what octane is used for SAE testing exactly, but the last sentence in the link below comes as no surprise. “The vehicle with the highest compression ratio technology showed the largest and most consistent octane appetite.”
https://www.sae.org/publications/tec.../2020-01-0619/

 

Make up a E 30 mixture using about 2.5 gallons of pump E85 with 6.5 gallons 93 octane which is E10, you will notice a difference , the C8 self tunes.

 

We got In-N-Out in Texas homie 😉

 

We saw similar results with the stock LS3, moving from GM's recommended 91 to 93. And to 94/95 in some cars. Data confirmed less KR, less timing pulled, and higher MAF throughput, not to mention higher trap speeds, if you're into those things. Once we started tuning, 95/96 became the sweet spot for those who could get that octane.

 

And that’s a 10.7:1 SCR port injection/fixed IVC engine vs 11.5:1 SCR direct injection/variable IVC which is more sensitive to octane I’d say.

 

I do not know anything about the effectiveness of mixing fuels fuels with ethanol to achieve effectively a higher octane. What I think I know is the the C8 will adjust timing automatically to take advantage of a a higher octane. It is engineered to do. And, I do not know that result will be noticeable but I strongly suspect it will.. Here are the reasons I think that.

The early manuals "required" 93 octane but said that 91 was acceptable. Do no go below 91. The later manuals said 91 was required. But a careful read in the Track Events and Competitive Driving section reveals that 93 octane or higher is required for tracking. To me that is strong indicator that the C8 is engineered to fully take advantage of that octane, or higher. I have seen folks post the timing data when using octane higher than 93, and claim the timing will advance even further with higher octane. But they will have to chime in on details of that. I do no know if it results in perceivable or measurable performance.

Here is the information form the Service Manual on how the engine adjusts the timing to adapt to different octane fuels. Essentially what is says is there is some nominal "zero compensation level" for timing advance and the ECM will always attempt to move the timing back to that target. It never says, but I am going to suggest (based on those forum posts where timing was measured) that the nominal timing advance designed for at least 93 octane or higher. I think (again a conclusion on my part) that when 91 Octane is used, the ECM is actually pulling the time back from the target timing. And, based on what the Owner's Manual says, I think it cannot accommodate an Octane belwo 91. Here is the description of the process.

"Knock Sensor
The knock sensor system enables the engine control module (ECM) to control the ignition timing for the best possible performance while protecting the engine from potentially damaging levels of detonation, also known as spark knock. The knock sensor system uses one or two flat response 2-wire sensors. The sensor uses piezo-electric crystal technology that produces an AC voltage signal of varying amplitude and frequency based on the engine vibration or noise level. The amplitude and frequency are dependant upon the level of knock that the knock sensor detects. The ECM receives the knock sensor signal through two isolated signal circuits for each knock sensor. The control module learns a minimum noise level, or background noise, at idle from the knock sensor and uses calibrated values for the rest of the RPM range. The control module uses the minimum noise level to calculate a noise channel. A normal knock sensor signal will ride within the noise channel. As engine speed and load change, the noise channel upper and lower parameters will change to accommodate the normal knock sensor signal, keeping the signal within the channel. In order to determine which cylinders are knocking, the control module only uses knock sensor signal information when each cylinder is near top dead center (TDC) of the firing stroke. If knock is present, the signal will range outside of the noise channel. If the control module has determined that knock is present, it will retard the ignition timing to attempt to eliminate the knock. The control module will always try to work back to a zero compensation level, or no spark retard. An abnormal knock sensor signal will stay outside of the noise channel or will not be present. knock sensor diagnostics are calibrated to detect faults with the knock sensor circuitry inside the control module, the knock sensor wiring, or the knock sensor voltage output. Some diagnostics are also calibrated to detect constant noise from an outside influence such as a loose/damaged component or excessive engine mechanical noise."

Someone mentioned in this thread about whether or not the ECM will "experiement" with the timing. I think that statement above "The control module will always try to work back to a zero compensation level, or no spark retard" does indeed suggest that the ECM will attempt to advance the timing until knock is just detected or until it reaches zero compensation level. I do not know if it does that continuously, periodically - and I assume that however it does it - its not noticeable to the operator.

 

Since it happens mostly in V4 mode, light load in high gear at 1250-1400 rpm, it seems timing related. Sometimes it will happen in V8 mode when rolling away from a stop slowly. I use 93 octane sometimes 94.

 

You are fortunate to have 91 octane non ethanol fuel. If you put in three gallons of E85 and the rest 91 octane non ethanol you will increase the octane in your tank to about 93 and not violate the 15% ethanol maximum stipulated by Chevrolet. Your car runs perfectly well on 91 octane but it will have a slight increase in power and torque on 93 (assuming you live at low altitudes). I submit that you may not feel the difference at anything but WOT.

 

Back to the ethanol argument - I've always liked E85 in terms of bang for the buck, but you do need the capability in the fuel system to tolerate and deliver it. Ethanol has less energy per molecule (enthalpy of combustion), but if you write out the chemical reaction equations from basic chemistry you see that many more molecules of ethanol combine with air as compared to gasoline, so the net effect is ethanol delivers a little more energy into the cylinder for a fixed amount of air. You also get this extra cylinder pressure from ethanol along with a lower exhaust gas temperature, as well as a lower manifold air temp after the ethanol vaporizes, so less heat transferred to the water jacket and inlet air. E15 gains will be less.

 

DA is density altitude , car runs super good in low DA IE 1000 versus 3000 and even better in minus DA

 

Yup and denser air increases cylinder pressure as I’m sure you know.

 

Last night I stopped at a local Kum and Go. It turns out this one has E85 and 91 no ethanol available on the same pump with separate hoses. I put 4 gallons of E85 in the tank and topped with 91. Haven't put many miles on but no CEL so far. Should be a fairly accurate mix depending on the percentage of ethanol that the E85 has.(sign on pump said minimum 70%) Last several previous tanks of fuel have been 91 no corn juice so I think it will be a good try out mix to see if there is any noticeable difference.

By the way the white car that was dynoed in the Paragon clips is a car local to this area. If I run into him, I will ask if it was box stock when those runs were recorded. He has made many changes over a period of time so could have been some unmentioned tweaks.

 

The Kum and go stations in Colorado have a very consistent 66% in their E85. This is what the ECU reports on my 19 Z06 that is flex fuel capable.

 

No, it's not. but timing advance doesn't change the CR. Nor does variable valve timing.

 

Sort of, but the engine doesn't pull timing based on the octane of the fuel. It has no sensor that tells the ECU what the octane of the fuel is. The ECU pulls timing when the knock sensors detect incipient knock. At low loads and moderate temps, even on 91 the engine isn't going to trigger the knock sensors. I suspect that even for short full throttle blasts the ECU won't pull timing. Under low loads, even 89 might work OK. But at high loads, high temps, track use, and other conditions the knock sensors are likely going to trigger spark retard with 91.

Related: Because timing is retarded ONLY when the ECU detects incipient knock, I doubt the ECU is actually tuned for higher than 93 octane. That would mean than when running 93 the engine is going to be verging on knock when under load. I don't think GM would want the engine running that close to knocking a lot of the time.

 

Variable valve timing doesn’t change the static compression ratio, but it does change the dynamic compression ratio which an earlier IVC will increase cylinder pressure as well as advancing the timing increases cylinder pressure.

Have you ever driven a 5.0L 12:1SCR F150? The thing is constantly on the verge of detonation trying to make as much lowend torque as possible and be as efficient as possible which means running as much timing as possible. Computers have gotten so good they’re running as much timing as possible to lessens emissions and it’s almost always pulling timing/adding it back as load varies.

 

Anyone try 260GT Sunoco gas ? I tried 1/4 tank of that + 3/4 93 in my 2017 GT350 once and it really did feel like it was different, revved way easier.
I might try a little in my C8.

 

I never said it sensed the octane in the post that you quoted. I said " the C8 will adjust timing automatically to take advantage of a a higher octane". And, in the part of my post that you did not include when you quoted me, I went on to say "Here is the information form the Service Manual on how the engine adjusts the timing to adapt to different octane fuels." And following that, I posted the description from the Service Manual that describes in some detail how the knock sensors are used to adjust the timing. Part of that description says ""The control module will always try to work back to a zero compensation level, or no spark retard". While it is a fact that the Owner's Manual says "Premium unleaded gasoline meeting ASTM specification D4814 with a posted octane rating (R+M)/2 of 91 or greater is required," and in the section on tracking it says "Unleaded gasoline, rated at 93 octane or higher, is required," it is speculation as to whether or not "zero compensation level" timing is optimized for 93 octane, or higher.

The final ignition timing is determined by the ECM, and it include inputs from the knock sensors, as well as other factors. There is an ignition timing parameter that is observable with a scan tool (as well as a few intermediate timing parameters), described as "displays the final spark advance in terms of crankshaft angle," but the range of values is not given in Service Manual. And the Service Manual that I have does not state anything about octane requirements other than to use " fuel that meets the vehicle minimum octane requirements."

 

Your C8 will respond to full strength E30 mixture because of the benefits of ethanol and the wide band tuning in our cars