Ooh, I feel some math coming on...
Hokay, let's get HP as a function of BMEP, displacement and RPM. Easy.
BMEP is in PSI and displacement is in cubic inches
If we take the crazy BMEP values some supercharged nitromethane dragsters are churning out (1450psi, which is absolutely mind boggling), and combine that with our displacement of 3.051 cubic inches, we get:
HP=368.6625psi cu-ft x (RPM/16500)
But what shall we use for our RPM? Well, RPM as a function of mean piston speed and stroke is defined by the following:
I'm going to use metric for this one just to be that guy. Let's stick with a slightly less that average moped stroke length of 39mm. That will get you a slightly oversquare engine, but would not limit you overly in terms of porting. As for mean piston speed, we will again delve into the world of top fuel drag racing and F1 lunacy to pull the absolutely insane number of 30m/s out of our asses.
Note: I am aware that mean piston speed is not actually a particularly useful number for engine design. It is, however, a fuck of a lot easier to calculate than max piston acceleration which is what you actually want. It's good enough for napkin math.
If we stick that into our earlier equation, we get:
HP=368.6625psi cu-ft x (23077RPM/16500)
That leaves us with a grand total of...
Disclaimer: that's a rough estimate on the back of an envelope and does not take into account air flow at all. It would be completely impossible to get anywhere near the amount of air required to do even 1/4 of that through the ports of a piston that small, even with ludicrous amounts of boost. It also doesn't take into account heat generation, which would probably require something like the cooling tower on a nuclear power plant to dissipate. It also also doesn't take into account the fact a piston or crank that would hold together at the peak acceleration generated by the piston speed we used would not be possible to construct with modern materials. I'd have to do that math, but I'd bet the acceleration would be in the ballpark of 10000g. So if you have a 100g piston, the force on the crank arm would be something like 10000N. Unless the internal bits of your engine are made of unobtanium, the sheer inertial forces would be enough to tear it apart. Finally, that number is the result of me cherry picking the highest numbers I could find from the kookiest corners of motorsports. Using these calculations, you could probably "prove" that your Civic can produce 4000HP.
But there you go, the maximum theoretical HP output of a single cylinder 50cc two stroke engine is 515. Assuming your crank and piston are made of magical pixie dust, you are running nitromethane, your engine is immersed in a bath of liquid nitrogen and there's a supercharger producing 500psi bolted to the side.