I finally did some testing today,8.8 to 1 360 with stock Edelbrock heads and a hydraulic cam. I tested all 3 grades of fuel from a local station that had the best 93 octane premium when I tested several a couple of years ago.
87 octane was the worst,110 VP wasn't far behind .
The 93 made less power than the mid grade,which I believe is 89 octane R/M2 I forgot to check that.
Overall best was the midgrade . I tested each for best power A/F and timing .
I will print some sheets out later,but the average difference between the premium and 110 after tuning was only around5 hp. Low speed torque was where a lot of difference was noticed .
Keith

I usually try not to post on this particuar forum since I'm a nobody............

but my understanding of low vs high octane gas is that the lower octane doesn't necessarily "burn faster" but is set-off/ignites sooner due to volatility. Meaning, when there is high compression the molecules being packed so tightly, low octane will not handle it as well (detonate on its own accord) as what higher octane will sustain. So high octane has a higher threshold than low compression motor even needs or will put upon it, hence the waste of $$$.

Once ignited, the burn rate is the same.

Pretty noticeable gains from best to worst
Keith

And torque
Keith

Interesting because mid-grade is generally a blend of the (87) regular and the (93) premium, there is no (not that I'm aware of anyplace I've seen) a seperate tank underneath the station for mid-grade, it's blended on-site at the pump(s).

Seems normal to me from the standpoint that any particular engine has a certain fuel it likes best. A blend might provide the best characteristics for a combo. If all other variables of tuning are optimized then its just a matter of fuel performance in the chamber for that combo. Just looking at octane numbers may not give us a total picture of what an engine performs best with.

Damon