[Formulajones]

Okay look, you were on here a couple months back asking questions about your compression, wanting to drive the car across country and needed solutions to your problem then. A lot of great advice was given by several members here and it appeared you didn't want to hear it then.

Now here we are.

To answer that first question of run on being an indication of detonation. The answer to that is NO.

You're getting run on because you have fuel remaining in the chamber, and it's igniting from the heat, throttle blades are most likely open too far. The low octane ignites when the key is shut off because of the extreme chamber heat, high compression, high heat range plugs, etc etc...

The only reason it goes away with more octane is because of the simple fact that higher octane is harder to ignite, it's slow burning. I explained this in post 20, and others have mentioned it as well. It doesn't mean your problem is fixed, it's just a bandaid to a larger issue. It doesn't necessarily mean your engine is detonating while you're driving it, but there is a pretty good chance you're causing damage trying to run 87 octane in a 11:1 motor with iron heads. But again we need more details on your state of tune. An engine like this is going to need spot on timing curves and close control of engine temps, as well as perfect AFR's if you are going to attempt to run this on pump gas, especially in the summer heat.
I have plenty of success doing this, my wife is daily driving an 11:1 engine on pump gas with iron heads and experiences absolutely NONE of these issues you're having. But I have close control over the parameters.

If your fine with spending $300 on additives to try and cure the issue, and don't mind dumping stuff in the tank every time you fill up, and happy with the results, then have at it. It's your car.
Seems to me it would be cheaper for you to just fill up with 91 or 93 instead of that cat pee 87, and tune the car accordingly for best all around drivability, and quit fooling with it. Better yet, for more piece of mind if you aren't confident in keeping control of the tune, I'd start looking at ways to lower dynamic compression with a cam change, or go straight for a set of aluminum heads that are more tolerable to octane levels so you can quit worrying about it. All things that were suggested in earlier threads.
Hope that helps.