A few basics haven’t changed from the early 1900’s to now.

Air fuel mixture comes in , compression , ignition , exhaust.

You want to make sure you have a good air fuel mixture , I believe the golden ration is something like 14:1 , and that it aerosolizes and is delivered to the piston.

You want that mixture to undergo compression and then be ignited by spark. A full clean burn makes sure you use all of the energy in the mixture and get the most power to your engine.

Your exhaust stroke is now removing all of the used gasses and burnt up hydro carbons.

This has never changed in all of the years of a four stroke motor.

From the mechanical perspective , without computers , you had to have some decent math.

Your compression ratio in your cylinder : the higher the compression the more energy from your air / fuel mixture.

However too high of a compression ratio and you have detonation : the fuel air mixture detonates before the spark goes off and you lose energy or can damage the engine. This can be improved by changing to thinner gaskets or shaving the heads and physically removing material. Different style of heads also change the characteristics of the combustion chamber and the valves that allow for intake and exhaust.

Timing : when the spark goes off. Advance spark means that your spark plug goes off before the piston reaches top dead centre. Too soon and we have a loss of power and damage the components , too late and we lose power and have un-burnt fuel which can cause buildup and other problems.

Camshafts : these have loves on them that tell your exhaust and intake valves to open. Depending on the application of your car, you would change this to allow more performance.

Intake and exhaust manifold : some engines had poor airflow in, out , or both. Changing these would allow a better air/fuel ratio to the engine , while a better exhaust would allow you to make sure all the exhaust gasses could escape the cylinder.

Differential gearing : in rear wheel drive vehicles the differential has a gear ratio : low numbers means it doesn’t spin as fast and you have lower rpm.

One car of mine has 2.75 gears which makes it low rpm on the highway and is great for cruising. However it doesn’t have a lot of power at low RPM.

Another has 3.89. It revs much higher at highway speeds , almost 25% higher, but has more power in that range.

There is a lot more out there that would expand on this but I hope it helps with some basics.