Originally Posted by willwren
The i doesn't mean anything. Other than the top trim level. SSE doesn't stand for anything either. This info is straight from Pontiac.
Methinks there is actually something in my service manuals about the distinction. Way back in the day, "SE" sometimes meant Special Edition, "SSE" could conceivably be, um, "Super Special Edition" (not Supercharged Special Edition); the "i" suffix has been variously used on different brands and years to mean "injected" (as opposed to carbureted), "intercooled" (for turbo applications) or "induction" (as in -- stretching it a little bit -- turbocharging or supercharging).
But yeah, it'* really subjective, not at all scientific, and guided more by Marketing geeks than real Engineering types, to the point that these designations are largely meaningless nowadays.