After changing oil and filter I forgot (?) to tighten the oil filter. I started the engine and after about 5 minutes idling I noticed that most of the oil was in the bilge instead of in the engine and there was no oil-pressure. I then immediately shut off the engine. I now wonder, is my smallblock dead now or seriously wounded or could it be still alive and kickin’ after new oil and a tight filter?

If the motor wasn't knocking you probably are safe. Obviously, re-oil AND tighten the filter. Think about cranking with the kill switch pulled or even with the spark plugs pulled to minumize load on the lower bearings. Crank the hell out of it! with a good battery you should develop some (not much) oil preasure just cranking it.

THEN - put the plugs back in. and start it.

Be attentive to the preasures you have now - compared to before, and obviously - if you have any kind of "knock" after it is running a short time, pull it down and rebuild.

If you weren't knocking @ shut off. I'd try to run it.

MAV

I would reprime the motor, with a drill prior just to make sure the jounals and oil galleys are full otherwise, you will recreate heat once again. If you do not have a drill pump, borrow one from someone or just purchase one, they are common. Just pull your disributor out, place the pump over your oil pump shaft and drill away for about 3 minutes then turn your engine over 90 Degrees each turn. You will go twice around till your back where you started.

This will ensure that all those berings and lifters have sufficient oil before you turn over your engine.

5 minutes is a long time without oil pressure, you created a lot of heat. You will know as soon as you put additional oil back in and start it.

It is better to be safe than sorry, good luck.

Haven't you watched the late night info-mercials? They run the engines WFO with no oil for how many minutes? LOL! Chances are you are OK since you heard no knocking. If your oil pressures are down some consider going to the next heavier weight of oil.
Maybe you caught it just as the pump quit picking it up.

If your engine is a hyd. lifter unit and you heard no clatter from collapsed lifters then you still had enough oil in your system to prevent damage, as long as you were only at idle as you said and not under load: Fill it up, pull the coil wire, crank till you see the O.P. gage move, reinstall coil wire, fire up and as previously stated, check to see that you have the same kind of pressure when operating under the same conditions as before the incident and if so, thank the boating gods for a big favor! --- Jer

I heard no knocking or no clatter so now I pray to the gods for life after running-with-no-oil-pressure.

Include an oil change or two (including filters) in quick succession to remove any stray contaminates (metal) from the system. Chissle open each oil filter and look between the pleats to see how much, if any, bearing material was lost.

BT

Keep in mind that it didn't run the entire five minutes without oil. It would take a while to pump it all out with the leak. My bet is that you'll be ok, just follow the advice above.