What happens if I use regular unleaded gas in a ...

Filling your car with fuel not according to the manufacturer instructions is not advisable. In this case, it will cost more as well. The higher octane, the fuel is, means it will ignite on higher compressions without a spark. In turn, this will cause knocking in the engine. Now, each engine is designed to have a specific compression ratio of it's own, without regarding to which fuel you use. And so, filling your car with higher octane fuel will not increase performance but will just cost more.

Most modern cars have knock sensors.  So the immediate result of using a fuel with insufficient octane is that the car retards its timing to prevent knocking and you notice a decrease in low-end power.

I would seriously not recommend running a super unleaded car on just unleaded. After a while it will damage the engine because the engine requires a certain burning ratio to the fuel, so what will eventually happen is the engine will suffer a shorter life span and a loss in power. My brother had a Subaru Impreza P1 which ran on Super unleaded and they forbid him to use just unleaded.

Nothing will happen it mite how a little pinging noise butt it will be ok just put the right fuel in next time.

Octaine ratings are ratings that tell you how fast fule burns. The designers of any perticular engine keep this in mind when they are deturmining how much horse power they need to move your car. the manufacture will then post what octaine rating is best for your engine. one tank of the lower rated fule will not hurt your engine, but continual use will. if you follow the manufacture's recomendations you should get more than 200,000 miles out of your car.

Ive been using regular for my car even though it says to use premium. Ive never had problems with it.