Will using wrong gas with versatune cause damage?

[ramiroflores]

I have my car tuned with versatune using 91 but I've curently got 87 in it. Will this cause any issues? Potential advantages or disadvantages? Should I clear the tune when I have 87 in? Does it still potentially produce more power with 87?

[Ugnius @ VersaTune]

Fuel octane rating specifies its resistance to knock (detonation). By requiring certain octane, a tune knows how much an engine can be safely "pushed" without causing knock. When you fill up with lower octane than requested, the tune will request higher performance than the fuel can deliver and the engine will knock. The ECU will notice that and try to compensate by reducing power, but that mechanism is not foolproof. Over time, engine knock will cause physical damage to the engine.
As a result, you always need to have at least the same octane fuel as required by the tune (higher octane is fine). If that is not possible, you can either add a can of octane booster to the tank or flash a different tune (or return to stock).
Do NOT drive the car with 91 octane tune and 87 octane fuel.