Hellcat - the aftermarket possibilties for a factory FI (forced induction) engine (GTi 1.8T for example) are far greater than an NA (Normally/Naturally Aspirated) 1.8L (Civic Si for example).
An ECU upgrade (chip) will realisticly get you about 35HP to the wheels (~50 crank) just buy upping boost and fuel pressure.
Downpipe, bigger intercooler, etc. You can pump out over 300 HP at the crank if you know what youre doing before a turbo swap.
WTF are you gonna do with a Civic? Throw a fart can on it and tint the windows?
Good luck getting that thing over 200HP/NA with bolt ons.
Little Japanese economy cars are just that. Little Japanese economy cars.
If you like autos from the land of the rising sun and need to go fast - get yourself a Supra, STi, EVO or an Rx7 - dont waste money on kids toys.