Aircraft engines?

Question

What does IO, O, TSIO means when in reference to different types of engines like the lycomings and continentals?

Answer 1

IO is (fuel) Injected Opposed

O is horizontally opposed cylinders (R means radial)

I think T is turbo

Don't remember "S"

Answer 2

IO = [Fuel] Injected Opposed  (Lycoming or Continental).

O = Opposed (Lycoming or Continental)

TSIO =  TurboSupercharged Injected Opposed (Continental only).

The Lycoming equivalent of TSIO is TIO (Turbocharged Injected Opposed).