However, higher octane can indirectly increase engine performance in one certain condition: under heavy throttle.
The computer can command more ignition advance. So the engine can extract more of the energy in the fuel.
I use 91 in the mountains. The difference from 87 is noticeable in that the van holds the higher gears longer before downshifting. If the hill isn't too long or too steep, I can sometimes slingshot (i.e. trade speed for throttle) over the top without any downshift at all.
Yes, this.
When I was towing my boat in the hottest summer months, I filled up with 91 octane. Under heavy throttle, and repeated trips to the lake and back, the increase in available power under that heavy load was noticeable. It was not earth-shattering, but it was definitely there...enough to convince me that 91 octane was the way to go when towing heavy.
As well, I ended up getting an extra round trip to the lake out of a tank of gas if I used the van only as a dedicated tow vehicle. Also, while filling my Odyssey with 91, I could fill up my small army of 5 gallon gas cans (each with 13 ounces of TC-W3 two-stroke oil for a 50:1 mix), because my big outboard needed 91 as well.
I've been up and down the Tejon Pass (I-5) and Cajon Pass (I-15) many times in our Odysseys, and after the first climbs using 87 with a family of six on board, I decided to switch to 91 for subsequent trips. Again, with heavy throttle, the beneficial difference in power from using 91 octane did show itself.
For all other conditions, at light throttle, I feel that 87 gave me the same range as 91...I couldn't discern a difference when tracking my range from tank to tank.
OF
