IC motors come in all shapes and configurations. There are: horizontally opposed, V, Inline, Rotary, Radial, Gas Turbine, H, W, F,Y, and I types (amongst even more obscure others). These motors come in everything from 1 to over twenty cylinders, or in some cases none at all. Most of the time when a letter is used to designate a configuration it is referring to the layout of the cylinders in relation to the crank case, but in many older motors it is referring to the layout of the valves. Im not even going to get started on cycles, and strokes.
Gas is gas, the Octane level in gas is best thought of as a representation of knock resistance, running lower than recommended will result in the computer trying to compensate, and eventually knock (and sooner or later a popped motor, especially in a Protege). Meanwhile using to highly rated octane gas in your car without the proper tune will result in your car barely able to maintain an idle, if it can run at all.
Oh and by the way If you can barely afford to put gas in the car than wait till
things start to break. This car will break you.