Do verados have a knock sensor and compensate for detonation?
 

yes and maybe

I cant directly tell you that Merc does or does not, but I can tell you from someone that works for a OEM that design engines, ANYTHING that is not NA has knock detection, and will pull timing till knock stops. You HAVE to design for a customer putting 85 oct when right on the cap it says 91 minimum. Seeing how much these outboards cost I would be good money they do all of the above.

Cool, is that what the 400 is really based off of?

All 4 strokes are going to have a knock sensor .It is needed to protect the engine.

Simon motor sports remaps verados. They will tell you you need to run 91 to get full benefit of the map. Going down to 85 might be strechting it. Timing can be retarded at the expense of performance.

There is a point where the gas will self ignite prematurely causing a knock. No amount of adjustment will stop that.

Hot spots and carbon build up may also cause pre-ignition.

I would ask whomever is doing the remapping as to what the minimum octane is required. I am guessing it would be 89.

If you are remapping I assume you want to run harder. Engines are more likely to knock the harder they are run. Lastly heat will play a factor when running marginal gas.

they have 2 knock sensors.