I was careful when choosing my words. The stock tuning does not benefit from using premium fuel. There are very few vehicles that are designed from the factory to re-tune the engine for premium fuel. I never said to use premium fuel with the 87 octane tune. I was referring to your claim that the engine does not "require it" and chemical knock retard.
You said that running premium is of no benefit unless your vehicle is tuned to run it i.e. advanced timing etc. I am simply agreeing with this and taking it one step further by questioning why should I run premium with the diablo tune when it is less or the same spark advance as my factory tune. I mean exactly why does the diablo tune benefit from running premium? I have read...you should run 93 with the diablotune because WOT timing is advanced alot....is it?
And how exactly are we leaning out the fuel mixture? We are supposed to adjust the LTF's by telling the ecm we have a different size injector than we actually have? But that is just so the ecm does not have to work so hard to correct the LTF's, right? So then when it calculates for PE it is using a false set of values? Then we are supposed to adjust PE to 12.5 to 13.
If I cannot feel a difference, then exactly what does this thing do again?
There are two different diablo tunes being conflated together. Your questions posed in prior posts I believe are pointed to timing settings when running the stock setting vs. 87 octane diablo tune. Neither of those tunes would warrant premium fuel.
The premium fuel should only be used when using the premium fuel tune.
In regards to LTFT, users notice significant mileage improvement and performance response when dialing-in the injector slopes. You would think otherwise but it works.
Furthermore, the PE fueling is a commanded setting so the fuel trims only act as modifiers to the PE values. The PCM is "guessing" what is needed during PE by adding/subtracting to the commanded/desired a/f ratio set. Adjusting your injector slope and PE values will help to get the most out of the engine regardless of fuel octane used.
You never tune timing settings until you have dialed the fuel settings because a excessive lean condition can cause spark knock under load so your timing adjustments would be made to correct a symptom caused something else.