How many miles or how long do 1991 G20 2L v4 engines last?

I don't know how long they go for but I have 268,000 miles on my 91 G20 and it still goes. I have been told that they can go over 300,000 miles no problem. I hope that this helps you.

Yeah i got a 93 Infiniti G20 and it has 230,000 miles on it and runs like a top !!

I've got a '93 G20,when I bought it,it had about 200,000 miles and it still had everything original on it! And I mean everything:spark plugs,spark plug wires,starter,oxygen sensor,distributor cap& rotor,fuel pump,I couldn't believe it! So I bought it right then,because any car that can haul like this one,with all those miles and OEM parts about fifteen years old, amazed me. Now it has 225,000 miles and shows no signs of stopping or weakening. The only parts that have gone out on this car has been: struts,ball joints,and starter. I think I can live with that!

Back to the "engine" question: Research the legendary "SR20DE" Nissan engine. Those are "overbuilt" from the factory to accommodate the turbocharger in certain car models (i.e. SR20DET). That mean the internals of the naturally-aspirated versions are "tougher than they need to be", particularly the bottom-end. Take care of it well and it will last for a very long time. Abuse it, and you will pay with very expensive repairs, especially now that the SR-engines are considered "legacy" types and parts will naturally be in shorter supply.