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

It will gum up you fuel injectors and take away from the performance of your car. It will also run crummy probably burning more gas too. All gas is expensive so don't take the chance in screwing your motor up over five or ten cents it really isn't worth it!

It depends on the year, make, and model of your car.  Some cars won't have a noticable affect, others may miss and run very poorly.

What happens is a term called detonation. the air fuel mixture ignights prematurely and can damage the pistons,valves. try adding lucas octane booster to reg unleaded. its good stuff!

if you switch gas it would cause a pinning/rattle sound in the valves.

worse fuel economy  less power  pre-ignition  and gummed up injectors over time if gas does not have cleaners

in most cases nothing will happen, if your car is controled by a compuetr module, newer cars have it, the computer wilkl automatically retard the spark as to avoid prignition {ping} and you may find a slight decrease in gas mileage, and slighlt slower oin performance. but unless it is a very hign performance requiring in excess of 95 octane you will not notice any differance.

I have several high performane vehicles, on states for maximum performance high test is reccommended, the other states high test is reccommended only i have used regular for the ast 4 years on the max performance reccommendation and have expierenced no problems, the other only when i go on a long distance trip to i use the regular and no problems,