Most GA piston singles are powered by either Lycoming or Continental engines.
The engine designs used by both manufacturers are broadly similar (4-cycle, horizontally-opposed, gasoline-powered, air-cooled), and they're both generally available with either carburetors or fuel injection, but I know they're not "identical products".
What are some of the differences between the designs used by the two manufacturers, and what practical implications do those choices have for pilots?
The larger Continentals have the alternator belt-driven off the back of the engine.
And Continental still builds the four-cylinder O-200, and a lightweight version of that engine, too.
Continentals cost more money.
Continental parts cost more money.
Continentals normally have more valve trouble than Lycomings.
Lycomings have better valves and guides.
A Lycoming usually has its carb mounted to the oil sump, either the bottom or rear, and feeds the cylinders via tubes cast into the sump and connecting tubing from there to the intakes. The heat of the oil wicks into the carb body and reduces the likelihood of carb ice.
Continentals mount the carb on a separate intake manifold that doesn't transfer that heat, so pilots trained on Lycs can get bitten by Continentals if they haven't been trained in the detection and management of carb ice.
The fuel injection systems used by Continental and Lycoming are somewhat different.
Continental numbers their cylinders back-to-front.
Lycoming numbers them front-to-back, and the staggering of the cylinders is opposite between the two.
Continentals, at least the smaller ones, have the right mag firing at the top plugs and the left firing the bottom.
One of Lyc's mags will fire the top plugs on one side and the bottom plugs on the other, with the other mag firing the rest.
Really, they just sorta look the same, with cooling fins on them and a propeller on the front and pistons inside that go up and down, and they both turn lots of money into smoke, but that's about it. If I was to buy one, it would be a Lycoming.
Lycoming engines have the camshaft above the crankshaft, and Continental engines have the cam below the crankshaft. This seems to keep the Conti cams better oiled and therefore less susceptible to corrosion.