Compression Ratio can be changed by:
Changing the crank shaft for a longer throw for higher compression or shorter for lower
Changing the pistons to a dome for higher compression ratio or concave for lower
Changing the head for a dome (lower) or flatter (higher)
Adding a shim and or thicker head gasket.
Add or modify the valve timing for a virtual compression ratio change
(the Prius and its "Atkinson Cycle Engine" uses this technique but it's not really an Atkinson Cycle, but that's a different rant.....)
ANYWAY....
Adding any supercharging, including a turbo charger increases the total compression ratio which is why turbo charged engines are as low as 6:1 to 8:1 while normally aspirated engines are 8:1 to 10:1 (up to 12:1 in some cases)
Which of these will work for the elio?
When making an OEM engine for mass production, a turbo charged engine should be optimized from the block, not just strapping on a turbo with some duct tape.
There are many considerations including rings, piston quality and fabrication, durability and also resonance for the longer throws and different components.
How much effort will supercharging an engine compared to designing a 4 cylinder?
Will a strengthened transmission, suspension, frame, mounts, etc be required?
What type of liability will be involved?
Of course, many here can, and will modify and upgrade the Elio, and this is a good thing.
But EM will look at a list like mine above (but MUCH longer) and ask 2 questions:
Can we?
and more importantly:
SHOULD we?