[Sburn]

Originally Posted by JackandJanet

And, even if it does need a reduction in timing, the manual recommends only 0.5 degrees for each octane point, so 93 down to 91 should only require a 1 degree reduction.

...

So anyway, I'd try resetting the spark change to 0 and see how it drives.

- Jack

Jack,

I was playing it very safe with the timing since my tank still had some 87 octane in it when I filled up with 91. I did a quick calculation of the mix ratio and gave it a little more retard to err on the side of caution.

Long term, I'm just a bit too thrifty to run anything but 87, so I'll probably go back to #2 tune, or maybe think about a custom #3 87 octane performance tune if there's any significant difference between that and the #2 87 towing tune.

Or....If the kind folks at PHP have a way to add a knock sensor or spark retard PID to the available Gryphon display gauges, then it would get easier to optimize the timing without going to far in the bad direction.