Originally Posted by BJ67

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

Originally Posted by jpmotorsport

After reading this thread I def want to try a gal or 2 of E85 , IF I can find some ...

Believe it or not where I am, I can get to a Sunoco that pumps 100 Octane 260GT in way less time than the nearest station with E85 ... 14.99/gal tho

Originally Posted by Andybump

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."

Originally Posted by PRE-Z06

It basically is sensing the octane though if it’s trying to run as much timing as possible without knock? Octane rating is just a measurement of resistance to detonation. You can therefore run a later IVC or less timing to lessen the chance of detonation on a lower octane with a relatively high compression ratio, which I think is what some may not understand. I built a 6.0 in my C5 that had 11.8:1 SCR though it had a 233 intake lobe on a 113+2, so it didn’t close as early as the smaller emissions compliant LT2 cam. A later IVC doesn’t build as much cylinder pressure all else equal, therefore it lowers the octane requirement or allows more timing. All I’m saying is I believe the timing tuning on the LT2 is pretty optimized with 93 fuel and the gains from “tuning” are more so from leaning out the 60k mile warranty safe factory tune, but someone else can correct me if I’m wrong.

Originally Posted by Andybump

Yes -it uses the knock sensors to adjust timing to accommodate a range of octanes from 91 up to 93 or higher (100 based on the info below). And max advance is (or was) 28 degrees. The correction varied from -18 degress to 0 degrees.

A while back @bhvrdr reported results when running blends of fuel above 93. With the stock tuning. He report that "The Corvette, however, is programmed from the factory with aggressive timing tables that in this case can take advantage of around 100 octane or e30 roughly......So on a car that is targeting 28 degrees of timing but only able to make around 18 degrees of timing on 91 octane you will see 10 degrees knock retard....So now you try 96 to 98 octane fuel or e20 to e25 and you see 24 to 25 degrees timing advance with 3 to 4 degrees of knock retard. I used to also see these timing numbers adding one bottle of Lucas octane booster to 93 octane (don't use that in cars with cars and cars under warranty).....So now you try 100 octane or e30 and see 28 degrees timing advance with no knock retard. Great deal!......Now finally you can try 105 octane ms109 to check your work and you will see the identical 28 degrees advance and no knock because you reached the max timing the car was programmed to target."

Interested readers can find it at post 10 here https://www.corvetteforum.com/forums...post1606815595

Anyway, that is one of the reasons I say that will, using the knock sensors, adjust the timing to accommodate different octanes between 91 and 98 or higher (apparently up to 100). It’s not a comment about the resulting performance - just a comment on how the timing can vary.