LS swap or keep the 305 in a square-body, talk me into or out of it

keep-the-305 vote, and i will be honest about why, it is not all engineering. my 86 is a survivor and the engine is the engine it left Janesville with, and that matters to me more than 6 miles a gallon does. when the day comes that the 305 is actually tired, i will rebuild it with a mild cam and a four barrel and have a 250 horse small block that still looks right under the hood of a 1986 truck.

that said, i am not going to pretend the LS is wrong. if your 305 is already worn out and the truck is a driver you are keeping forever, 2,700 for a modern drivetrain that gets 18 on the road is not a bad deal, it is a good one. my line is simple: if the original engine still runs, keep it. if it is junk anyway, the LS math makes sense and the shiny-engine purists can get over it.

there is a middle road nobody in the LS camp wants to admit exists, which is where i live. i kept my 350 and put EFI on it instead of swapping. i get the cold-start-and-drive part of what the LS guys love without pulling the engine or touching the mounts, the pan or the trans. it was less money and a long weekend instead of a summer.

i am not saying it makes the same power as a 5.3, it does not. but if your reason for wanting the LS is "i am tired of babying a carburetor in January," you can fix that without a whole drivetrain swap, and your truck still has its own engine in it. i wrote the whole thing up in the carb to EFI thread if you want the gory parts.

ls_swap_or_keep your numbers are fair and that is why i am not arguing with the swap, i am just saying know what problem you are actually solving before you pull a good engine.

this is the exact argument happening in my own head about my 85. the 305 in mine runs fine, a little tired, and every fiber of me wants the LS because i drive the truck a lot and the mileage would pay for itself eventually. but it runs fine. that is the trap, right? the 305 is never bad enough to justify the swap and never good enough to make you stop thinking about it.

reading this i think my answer is drive it until the 305 actually needs something major, then decide with an engine out instead of an engine running. no sense pulling a 305 that still has life just because a 5.3 is 900 dollars at the yard.

good thread, and nobody is being a jerk about it, which on the internet about LS swaps is its own small miracle.

one thing from the parts-and-paperwork side. if you do swap, keep every bit of the donor documentation and take pictures of the donor VIN and the engine stampings before it leaves the yard. the day you sell the truck, a buyer wants to know what is in it, and a California truck with an engine swap has emissions rules you want to be on the right side of. a correct swap that keeps the LS emissions equipment is legal a lot of places a hacked one is not, and the current crate and engine information straight from the maker is at chevrolet.com if you are buying new instead of yard-pulling.

for what it is worth i am a keep-the-original man, but i ran a fleet long enough to respect anything that starts on the first cold morning without a prayer. both answers in this thread are right for the truck they are attached to.

brand new to all of this and reading everything before i buy my first old truck, so this thread is gold. honest question from the cheap seats: if i am shopping and i find two square-bodies at the same price, one with a running stock 305 and one somebody already LS swapped, which is the safer buy for a first-timer who cannot weld and barely wrenches.

my gut says the stock one is simpler to understand and fix, but the swapped one already has the thing everybody here says is nice. no idea which gut to trust.