Do I have a dropped valve?

[Antonio Garcia]

Hope everyone had a good Thanksgiving weekend,

Here's an update on my 118k mile SR20 that seemingly for no reason
started making a bunch of loud noises, specifically from the head area
of cylinder #4.

I did a compression check today with the engine cold, but here's what I
got. 185, 185, 185, 0. The engine still runs if I start it, but it
doesn't sound like it's running on 3 cylinders. Also, the loud noise
that is heard when the car is on was not heard while the motor was
cranked for the compression test.

The zero compression reading on #4 leads me to believe one of the
valves dropped or partially dropped somehow. If so, could I just swap
the head and be done with it? Is it possible that this presumed dropped
valve could cause other damage, like scoring of the cyliner walls?
Piston damage? I haven't run the car much (maybe for 2 mins max of
running time since the noise began), but I would like to get it fixed
asap as it is my daily driver.

Anyone input is appreciated. Thanks!

Antonio Garcia
91 SE-R w/ DET
91 SE-R, broken daily driver