Do I rebuild my SBC or swap for an LS3?

[OneShot]

All,

Not looking for help with an LS swap - that horse has been beaten to death. I'm looking for your opinions on my current situation. I use my C20 as a backup vehicle, and as a farm truck in weekly use. Its in very good original condition and not restored. I don't plan to make it a road queen - it's my truck. I use it as such. Probably going to throw a Detroit locker at it at some point.

It has a 350 that's getting long in the tooth. Consuming some oil, leaking valve guide(s?), making some noises I don't like, etc. To make things simpler, just consider the engine stock. I have the 991 heads and a 4-bolt main block driving an SM465 and 4.10 gears.

My question - do you think its worth rebuilding this engine and throwing some better (Vortec) heads at it, or should I swap it for an LS3? If LS, I'd try and find a 6.0 but I suppose a 5.3 would do. Not concerned with technical difficulty of either, but input on the amount of work you think each would be is welcome.

Edit: I plan to retain the SM465 either way unless someone makes a good case for doing otherwise.

Thanks,

 

[SirRobyn0]

Your about to get a lot of varied responses I'm sure. For my truck, (and if your truck was mine I'd do the same) so I daily mine into the city 4 days a week to the shop I manage. It's also my farm truck and gets used as a truck. It's in very good original condition, and like you it's my truck and I use it as such.

If it was me I'd rebuild the 350. Personally I would not put vortec heads on it given there are some folks who seem to have cold weather runabilty issues with a carbed vortec, but I'd put vortec heads on it before an LS or LS3 though. It's old truck keep it old technology. I'd do a stroker before any of that. My plan when the time comes is either a stock build 350 or a stroker built with towing and hauling in mind.

But that's just me, and like I said there will likely be lots of varied opinions to follow.

 

[Frankenchevy]

If you can afford the swap, the down time and can get a known good donor; an LS will outperform an old school SBC with similar mods done. If you can’t afford the downtime or 2-3x what you think a junkyard LS swap would cost, forget about the LS swap. If you just need your truck to be a workhorse, consider a BBC. If you’re all loaded up and working the thing, mpg will be similar. If you are commuting empty often, that’s different.

 

[Midnightmoon]

I have had a block at a local machine shop for literally almost a year and it still isn't back yet. Hopefully, the shops in your area aren't as completely understaffed and incompetent as the one I am dealing with. But, downtime may be a concern if you decide to rebuild.

 

[Shorty81]

Check out Skip White stroker rotating assemblies. Good stuff at decent prices. Or like stated above, BBC

 

[SquareRoot]

LS, NV4500 and EFI. Nothing more to say.

 

[Vbb199]

Crate 350, have it running again in a couple weekends, no guess work or complicated swapping involved

 

[OneShot]

Your about to get a lot of varied responses I'm sure.

Yeah, that's what I'm hoping for. Looking for some input I may not have considered.

If it was me I'd rebuild the 350. Personally I would not put vortec heads on it given there are some folks who seem to have cold weather runabilty issues with a carbed vortec

Huh, I had not heard of these cold start issues. I rebuilt my Quadrajet in 2019 and its performing great. Got it tuned in just how I like it. But this is concerning. Definitely cause for more reading.

If you can afford the swap, the down time and can get a known good donor; an LS will outperform an old school SBC with similar mods done. If you can’t afford the downtime or 2-3x what you think a junkyard LS swap would cost, forget about the LS swap. If you just need your truck to be a workhorse, consider a BBC. If you’re all loaded up and working the thing, mpg will be similar. If you are commuting empty often, that’s different.

This is my primary concern with an LS... finding a decent donor LS. I would want one under 100k mi OR I would rebuild it before going in the truck. I know that's a tall order from a junkyard. BBC might not be a bad idea.

 

[AyWoSch Motors]

KEEP THE 350!!! Please. You regret an LS swap..
Rebuild or get a new one. Any which way shape or form I'd take a small block first. After that, big block it, or no one has mentioned this, diesel swap.
If your looking for durability, good towing, and good milage, and your not trying to make a race truck, I'd go old school 6.2 or 6.5.
But I'd definatly keep the 350 if at all possible.

 

[Catbox]

My truck is pretty much your truck with the exception of mine has a 454.

If I were in your shoes, I would rebuild the current engine.
While in there I would also change out the stock cam for something with more grunt to it.
Do the simple bolt on stuff with an aftermarket intake and a set of quality headers.

That would be pretty simple to make happen.

 

[DoubleDingo]

I vote crate engine. It is way easier and faster to get back up and running, and then you have a fresh engine. You go buy the engine, pull the old one from the vehicle, swap over accessories, install the new engine, hook everything up, break-in the cam, change the oil, and then break-in the engine. It's that simple. Over the course of a weekend you could have a fresh powerplant in your truck and be back on the road.

 

[Elliot W]

As I'm in the middle of an LS swap....by the way you describe your needs from your truck, I'd recommend staying with a 350. The LS swap is great and all (or should be when I finish it) but doing the swap isn't always as simple as it seems. There are some annoying things that you'll have to address for the LS swap. My top three things I wish I didn't have to do/figure out when doing the LS swap is:
1. Figure out, find, and buy a fuel pump, sending unit, and baffled fuel tank.
2. Figure out your cluster items as the oil pressure and temp lines have different sensors/adapters/locations, same with the speed sensor depending on the transmission.
3. The transmission/drivetrain situation. I don't know the SM465 transmission well, but I assume you could use a BBC bellhousing to attach 4 bolts to the LS block. Like what squareroot said...you could go nv4500 for a proper transmission for the LS, but sourcing those might not be pleasant. Then with a different transmission comes possibly a different crossmember, driveshaft length, and switching from mechanical to hydraulic clutches.

I am doing the LS in my C10 because I want to learn how to do an LS swap, and the c10 I got came with a 5.3 in the bed (no transmission, just a sad saginaw 3 speed hanging out the bottom). From what it sounds like, you want your truck to be healthy and back in service shortly. If you don't want to get a crate motor, you could try for a cheap junkyard 350 and get it all dressed up before taking your trucks 350 out of service and have it ready to swap in immediately, not having the change out transmissions, sensors, clutches etc.

For what its worth, if you want something a bit more modern while keeping it mostly old school, consider a Holley Sniper EFI or the like. I put one on my other car and so far so good.

 

[TotalyHucked]

I LS swapped my '85 2 years ago. I drive the hell out of my truck, long roadtrips with friends, to truck shows, vacations, I wanted good power and mileage and I'm most experienced with LS motors. That said, it sounds like the way you use your truck, I'd probably just drop another small block back in it. IF you're able to find a low mile LS in a junkyard, everybody knows about the LS swaps so you're going to have to pay a premium for it, then you have the cost of a harness and tune, adapter for the trans, yada yada. It adds up quick. You'll easily be in it more than a crate small block. My swap ended up costing double what I originally thought.

 

[OldBlueDually]

I would personally re-build the 350 you have. All would be fresh, and last the life of the truck.

The crate 350 would be another great choice.

 

[SirRobyn0]

Huh, I had not heard of these cold start issues. I rebuilt my Quadrajet in 2019 and its performing great. Got it tuned in just how I like it. But this is concerning. Definitely cause for more reading.

No not cold start, cold weather runabilty. The suspicion is not being able to keep the intake warm enough to keep the fuel suspended. So in cold weather rough idle and hesitation I think is the main problem. If @77 K20 see this maybe he'd come in and tell you about his experience.